Op 09-09-2021 om 10:22 schreef Peter Zijlstra:

On Thu, Sep 09, 2021 at 07:38:06AM +0200, Maarten Lankhorst wrote:

...

...

You'll need a similar hunk in ww_rt_mutex.c

What tree has that file?

Linus' tree should have it. Per commit:

f8635d509d80 ("locking/ww_mutex: Implement rtmutex based ww_mutex API functions")

Ah yeah, it seems the drm integration tree missed it.

I only compile tested it against PREEMPT_RT, though it seems locking_selftests and fs/inode.c don't build correctly for me.

Improved patch below.

Also hopefully addressed Daniel's concerns.

-------8<------

From d7e867f26b7e2553b0e5b9b5b87a284467b85846 Mon Sep 17 00:00:00 2001

From: Maarten Lankhorst maarten.lankhorst@linux.intel.com Date: Fri, 3 Sep 2021 10:59:49 +0200 Subject: [PATCH] kernel/locking: Add context to ww_mutex_trylock, v2.

i915 will soon gain an eviction path that trylock a whole lot of locks for eviction, getting dmesg failures like below:

BUG: MAX_LOCK_DEPTH too low! turning off the locking correctness validator. depth: 48 max: 48! 48 locks held by i915_selftest/5776: #0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160 #1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915] #2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915] #3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915] #4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] ... #46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] INFO: lockdep is turned off.

Fixing eviction to nest into ww_class_acquire is a high priority, but it requires a rework of the entire driver, which can only be done one step at a time.

As an intermediate solution, add an acquire context to ww_mutex_trylock, which allows us to do proper nesting annotations on the trylocks, making the above lockdep splat disappear.

This is also useful in regulator_lock_nested, which may avoid dropping regulator_nesting_mutex in the uncontended path, so use it there.

TTM may be another user for this, where we could lock a buffer in a fastpath with list locks held, without dropping all locks we hold.

Changes since v1: - Rebase on top of the ww_rt_mutex rework. - Add extern to ww_mutex_trylock header definition. - Expand commit message slightly.

Signed-off-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Peter Zijlstra peterz@infradead.org Cc: Ingo Molnar mingo@redhat.com Cc: Will Deacon will@kernel.org Cc: Waiman Long longman@redhat.com Cc: Boqun Feng boqun.feng@gmail.com Cc: Liam Girdwood lgirdwood@gmail.com Cc: Mark Brown broonie@kernel.org Cc: linux-kernel@vger.kernel.org --- drivers/gpu/drm/drm_modeset_lock.c | 2 +- drivers/regulator/core.c | 2 +- include/linux/dma-resv.h | 2 +- include/linux/ww_mutex.h | 15 +----- kernel/locking/mutex.c | 38 +++++++++++++ kernel/locking/test-ww_mutex.c | 86 ++++++++++++++++++++++-------- kernel/locking/ww_rt_mutex.c | 12 +++++ lib/locking-selftest.c | 2 +- 8 files changed, 121 insertions(+), 38 deletions(-)

diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c index fcfe1a03c4a1..bf8a6e823a15 100644 --- a/drivers/gpu/drm/drm_modeset_lock.c +++ b/drivers/gpu/drm/drm_modeset_lock.c @@ -248,7 +248,7 @@ static inline int modeset_lock(struct drm_modeset_lock *lock, if (ctx->trylock_only) { lockdep_assert_held(&ctx->ww_ctx);

- if (!ww_mutex_trylock(&lock->mutex)) + if (!ww_mutex_trylock(&lock->mutex, NULL)) return -EBUSY; else return 0; diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c index ca6caba8a191..f4d441b1a8bf 100644 --- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -145,7 +145,7 @@ static inline int regulator_lock_nested(struct regulator_dev *rdev,

mutex_lock(&regulator_nesting_mutex);

- if (ww_ctx || !ww_mutex_trylock(&rdev->mutex)) { + if (!ww_mutex_trylock(&rdev->mutex, ww_ctx)) { if (rdev->mutex_owner == current) rdev->ref_cnt++; else diff --git a/include/linux/dma-resv.h b/include/linux/dma-resv.h index 9100dd3dc21f..5de7956818a5 100644 --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -262,7 +262,7 @@ static inline int dma_resv_lock_slow_interruptible(struct dma_resv *obj, */ static inline bool __must_check dma_resv_trylock(struct dma_resv *obj) { - return ww_mutex_trylock(&obj->lock); + return ww_mutex_trylock(&obj->lock, NULL); }

/** diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h index 29db736af86d..bb763085479a 100644 --- a/include/linux/ww_mutex.h +++ b/include/linux/ww_mutex.h @@ -28,12 +28,10 @@ #ifndef CONFIG_PREEMPT_RT #define WW_MUTEX_BASE mutex #define ww_mutex_base_init(l,n,k) __mutex_init(l,n,k) -#define ww_mutex_base_trylock(l) mutex_trylock(l) #define ww_mutex_base_is_locked(b) mutex_is_locked((b)) #else #define WW_MUTEX_BASE rt_mutex #define ww_mutex_base_init(l,n,k) __rt_mutex_init(l,n,k) -#define ww_mutex_base_trylock(l) rt_mutex_trylock(l) #define ww_mutex_base_is_locked(b) rt_mutex_base_is_locked(&(b)->rtmutex) #endif

@@ -339,17 +337,8 @@ ww_mutex_lock_slow_interruptible(struct ww_mutex *lock,

extern void ww_mutex_unlock(struct ww_mutex *lock);

-/** - * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context - * @lock: mutex to lock - * - * Trylocks a mutex without acquire context, so no deadlock detection is - * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise. - */ -static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock) -{ - return ww_mutex_base_trylock(&lock->base); -} +extern int __must_check ww_mutex_trylock(struct ww_mutex *lock, + struct ww_acquire_ctx *ctx);

/*** * ww_mutex_destroy - mark a w/w mutex unusable diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index d456579d0952..791c28005eef 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -736,6 +736,44 @@ __ww_mutex_lock(struct mutex *lock, unsigned int state, unsigned int subclass, return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true); }

+/** + * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context + * @lock: mutex to lock + * @ctx: optional w/w acquire context + * + * Trylocks a mutex with the optional acquire context; no deadlock detection is + * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise. + * + * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is + * specified, -EALREADY and -EDEADLK handling may happen in calls to ww_mutex_lock. + * + * A mutex acquired with this function must be released with ww_mutex_unlock. + */ +int __sched +ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ctx) +{ + bool locked; + + if (!ctx) + return mutex_trylock(&ww->base); + +#ifdef CONFIG_DEBUG_MUTEXES + DEBUG_LOCKS_WARN_ON(ww->base.magic != &ww->base); +#endif + + preempt_disable(); + locked = __mutex_trylock(&ww->base); + + if (locked) { + ww_mutex_set_context_fastpath(ww, ctx); + mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ctx->dep_map, _RET_IP_); + } + preempt_enable(); + + return locked; +} +EXPORT_SYMBOL(ww_mutex_trylock); + #ifdef CONFIG_DEBUG_LOCK_ALLOC void __sched mutex_lock_nested(struct mutex *lock, unsigned int subclass) diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c index 3e82f449b4ff..d63ac411f367 100644 --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -16,6 +16,15 @@ static DEFINE_WD_CLASS(ww_class); struct workqueue_struct *wq;

+#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH +#define ww_acquire_init_noinject(a, b) do { \ + ww_acquire_init((a), (b)); \ + (a)->deadlock_inject_countdown = ~0U; \ + } while (0) +#else +#define ww_acquire_init_noinject(a, b) ww_acquire_init((a), (b)) +#endif + struct test_mutex { struct work_struct work; struct ww_mutex mutex; @@ -36,7 +45,7 @@ static void test_mutex_work(struct work_struct *work) wait_for_completion(&mtx->go);

if (mtx->flags & TEST_MTX_TRY) { - while (!ww_mutex_trylock(&mtx->mutex)) + while (!ww_mutex_trylock(&mtx->mutex, NULL)) cond_resched(); } else { ww_mutex_lock(&mtx->mutex, NULL); @@ -109,19 +118,38 @@ static int test_mutex(void) return 0; }

-static int test_aa(void) +static int test_aa(bool trylock) { struct ww_mutex mutex; struct ww_acquire_ctx ctx; int ret; + const char *from = trylock ? "trylock" : "lock";

ww_mutex_init(&mutex, &ww_class); ww_acquire_init(&ctx, &ww_class);

- ww_mutex_lock(&mutex, &ctx); + if (!trylock) { + ret = ww_mutex_lock(&mutex, &ctx); + if (ret) { + pr_err("%s: initial lock failed!\n", __func__); + goto out; + } + } else { + if (!ww_mutex_trylock(&mutex, &ctx)) { + pr_err("%s: initial trylock failed!\n", __func__); + goto out; + } + }

- if (ww_mutex_trylock(&mutex)) { - pr_err("%s: trylocked itself!\n", __func__); + if (ww_mutex_trylock(&mutex, NULL)) { + pr_err("%s: trylocked itself without context from %s!\n", __func__, from); + ww_mutex_unlock(&mutex); + ret = -EINVAL; + goto out; + } + + if (ww_mutex_trylock(&mutex, &ctx)) { + pr_err("%s: trylocked itself with context from %s!\n", __func__, from); ww_mutex_unlock(&mutex); ret = -EINVAL; goto out; @@ -129,17 +157,17 @@ static int test_aa(void)

ret = ww_mutex_lock(&mutex, &ctx); if (ret != -EALREADY) { - pr_err("%s: missed deadlock for recursing, ret=%d\n", - __func__, ret); + pr_err("%s: missed deadlock for recursing, ret=%d from %s\n", + __func__, ret, from); if (!ret) ww_mutex_unlock(&mutex); ret = -EINVAL; goto out; }

+ ww_mutex_unlock(&mutex); ret = 0; out: - ww_mutex_unlock(&mutex); ww_acquire_fini(&ctx); return ret; } @@ -150,7 +178,7 @@ struct test_abba { struct ww_mutex b_mutex; struct completion a_ready; struct completion b_ready; - bool resolve; + bool resolve, trylock; int result; };

@@ -160,8 +188,13 @@ static void test_abba_work(struct work_struct *work) struct ww_acquire_ctx ctx; int err;

- ww_acquire_init(&ctx, &ww_class); - ww_mutex_lock(&abba->b_mutex, &ctx); + ww_acquire_init_noinject(&ctx, &ww_class); + if (!abba->trylock) + ww_mutex_lock(&abba->b_mutex, &ctx); + else + WARN_ON(!ww_mutex_trylock(&abba->b_mutex, &ctx)); + + WARN_ON(READ_ONCE(abba->b_mutex.ctx) != &ctx);

complete(&abba->b_ready); wait_for_completion(&abba->a_ready); @@ -181,7 +214,7 @@ static void test_abba_work(struct work_struct *work) abba->result = err; }

-static int test_abba(bool resolve) +static int test_abba(bool trylock, bool resolve) { struct test_abba abba; struct ww_acquire_ctx ctx; @@ -192,12 +225,18 @@ static int test_abba(bool resolve) INIT_WORK_ONSTACK(&abba.work, test_abba_work); init_completion(&abba.a_ready); init_completion(&abba.b_ready); + abba.trylock = trylock; abba.resolve = resolve;

schedule_work(&abba.work);

- ww_acquire_init(&ctx, &ww_class); - ww_mutex_lock(&abba.a_mutex, &ctx); + ww_acquire_init_noinject(&ctx, &ww_class); + if (!trylock) + ww_mutex_lock(&abba.a_mutex, &ctx); + else + WARN_ON(!ww_mutex_trylock(&abba.a_mutex, &ctx)); + + WARN_ON(READ_ONCE(abba.a_mutex.ctx) != &ctx);

complete(&abba.a_ready); wait_for_completion(&abba.b_ready); @@ -249,7 +288,7 @@ static void test_cycle_work(struct work_struct *work) struct ww_acquire_ctx ctx; int err, erra = 0;

- ww_acquire_init(&ctx, &ww_class); + ww_acquire_init_noinject(&ctx, &ww_class); ww_mutex_lock(&cycle->a_mutex, &ctx);

complete(cycle->a_signal); @@ -581,7 +620,9 @@ static int stress(int nlocks, int nthreads, unsigned int flags) static int __init test_ww_mutex_init(void) { int ncpus = num_online_cpus(); - int ret; + int ret, i; + + printk(KERN_INFO "Beginning ww mutex selftests\n");

wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0); if (!wq) @@ -591,17 +632,19 @@ static int __init test_ww_mutex_init(void) if (ret) return ret;

- ret = test_aa(); + ret = test_aa(false); if (ret) return ret;

- ret = test_abba(false); + ret = test_aa(true); if (ret) return ret;

- ret = test_abba(true); - if (ret) - return ret; + for (i = 0; i < 4; i++) { + ret = test_abba(i & 1, i & 2); + if (ret) + return ret; + }

ret = test_cycle(ncpus); if (ret) @@ -619,6 +662,7 @@ static int __init test_ww_mutex_init(void) if (ret) return ret;

+ printk(KERN_INFO "All ww mutex selftests passed\n"); return 0; }

diff --git a/kernel/locking/ww_rt_mutex.c b/kernel/locking/ww_rt_mutex.c index 3f1fff7d2780..c4cb863edb4c 100644 --- a/kernel/locking/ww_rt_mutex.c +++ b/kernel/locking/ww_rt_mutex.c @@ -50,6 +50,18 @@ __ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx, return ret; }

+int __sched +ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) +{ + int locked = rt_mutex_trylock(&lock->base); + + if (locked && ctx) + ww_mutex_set_context_fastpath(lock, ctx); + + return locked; +} +EXPORT_SYMBOL(ww_mutex_trylock); + int __sched ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c index 161108e5d2fe..71652e1c397c 100644 --- a/lib/locking-selftest.c +++ b/lib/locking-selftest.c @@ -258,7 +258,7 @@ static void init_shared_classes(void) #define WWAF(x) ww_acquire_fini(x)

#define WWL(x, c) ww_mutex_lock(x, c) -#define WWT(x) ww_mutex_trylock(x) +#define WWT(x) ww_mutex_trylock(x, NULL) #define WWL1(x) ww_mutex_lock(x, NULL) #define WWU(x) ww_mutex_unlock(x)

On Mon, Sep 13, 2021 at 10:42:36AM +0200, Maarten Lankhorst wrote:

...

+/**

• • ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
• • @ww: mutex to lock
• • @ww_ctx: optional w/w acquire context
• • Trylocks a mutex with the optional acquire context; no deadlock detection is
• • possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
• • Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
• • specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
• • A mutex acquired with this function must be released with ww_mutex_unlock.
• */

+int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx) +{

• if (!ww_ctx)

• return mutex_trylock(&ww->base);
  

• MUTEX_WARN_ON(ww->base.magic != &ww->base);
• if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))

• return -EALREADY;
  

I'm not 100% sure this is a good idea, because it would make the trylock weird. For i915 I checked manually, because I didn't want to change the function signature. This is probably the other extreme.

"if (ww_mutex_trylock())" would look correct, but actually be wrong and lead to double unlock without adjustments. Maybe we could make a ww_mutex_trylock_ctx_err, which would return -EALREADY or -EBUSY on failure, and 0 on success? We could keep ww_mutex_trylock without ctx, probably just #define as (!ww_mutex_trylock_ctx_err(lock, NULL))

Urgh, yeah. Also, I suppose that if we already own it, we'll just fail the trylock anyway. Let me take this out.

...

• /*

• * Reset the wounded flag after a kill. No other process can
  

• * race and wound us here, since they can't have a valid owner
  

• * pointer if we don't have any locks held.
  

• */
  

• if (ww_ctx->acquired == 0)

• ww_ctx->wounded = 0;
  

Yeah I guess this needs fixing too. Not completely sure since trylock wouldn't do the whole ww dance, but since it's our first lock, probably best to do so regardless so other users don't trip over it.

This is actually critical, because if this trylock is the first lock acquisition for the context, there won't be any other opportunity to reset this value.

...

• if (__mutex_trylock(&ww->base)) {

• ww_mutex_set_context_fastpath(ww, ww_ctx);
  

• mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
  

• return 1;
  

• }
• return 0;

+} +EXPORT_SYMBOL(ww_mutex_trylock);

Updated version below...

--- Subject: kernel/locking: Add context to ww_mutex_trylock() From: Maarten Lankhorst maarten.lankhorst@linux.intel.com Date: Thu, 9 Sep 2021 11:32:18 +0200

From: Maarten Lankhorst maarten.lankhorst@linux.intel.com

i915 will soon gain an eviction path that trylock a whole lot of locks for eviction, getting dmesg failures like below:

BUG: MAX_LOCK_DEPTH too low! turning off the locking correctness validator. depth: 48 max: 48! 48 locks held by i915_selftest/5776: #0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160 #1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915] #2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915] #3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915] #4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] ... #46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] INFO: lockdep is turned off.

Fixing eviction to nest into ww_class_acquire is a high priority, but it requires a rework of the entire driver, which can only be done one step at a time.

As an intermediate solution, add an acquire context to ww_mutex_trylock, which allows us to do proper nesting annotations on the trylocks, making the above lockdep splat disappear.

This is also useful in regulator_lock_nested, which may avoid dropping regulator_nesting_mutex in the uncontended path, so use it there.

TTM may be another user for this, where we could lock a buffer in a fastpath with list locks held, without dropping all locks we hold.

[peterz: rework actual ww_mutex_trylock() implementations] Signed-off-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org --- drivers/gpu/drm/drm_modeset_lock.c | 2 drivers/regulator/core.c | 2 include/linux/dma-resv.h | 2 include/linux/ww_mutex.h | 15 ------ kernel/locking/mutex.c | 41 +++++++++++++++++ kernel/locking/test-ww_mutex.c | 86 +++++++++++++++++++++++++++---------- kernel/locking/ww_rt_mutex.c | 25 ++++++++++ lib/locking-selftest.c | 2 8 files changed, 137 insertions(+), 38 deletions(-)

--- a/drivers/gpu/drm/drm_modeset_lock.c +++ b/drivers/gpu/drm/drm_modeset_lock.c @@ -248,7 +248,7 @@ static inline int modeset_lock(struct dr if (ctx->trylock_only) { lockdep_assert_held(&ctx->ww_ctx);

- if (!ww_mutex_trylock(&lock->mutex)) + if (!ww_mutex_trylock(&lock->mutex, NULL)) return -EBUSY; else return 0; --- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -145,7 +145,7 @@ static inline int regulator_lock_nested(

mutex_lock(&regulator_nesting_mutex);

- if (ww_ctx || !ww_mutex_trylock(&rdev->mutex)) { + if (!ww_mutex_trylock(&rdev->mutex, ww_ctx)) { if (rdev->mutex_owner == current) rdev->ref_cnt++; else --- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -173,7 +173,7 @@ static inline int dma_resv_lock_slow_int */ static inline bool __must_check dma_resv_trylock(struct dma_resv *obj) { - return ww_mutex_trylock(&obj->lock); + return ww_mutex_trylock(&obj->lock, NULL); }

/** --- a/include/linux/ww_mutex.h +++ b/include/linux/ww_mutex.h @@ -28,12 +28,10 @@ #ifndef CONFIG_PREEMPT_RT #define WW_MUTEX_BASE mutex #define ww_mutex_base_init(l,n,k) __mutex_init(l,n,k) -#define ww_mutex_base_trylock(l) mutex_trylock(l) #define ww_mutex_base_is_locked(b) mutex_is_locked((b)) #else #define WW_MUTEX_BASE rt_mutex #define ww_mutex_base_init(l,n,k) __rt_mutex_init(l,n,k) -#define ww_mutex_base_trylock(l) rt_mutex_trylock(l) #define ww_mutex_base_is_locked(b) rt_mutex_base_is_locked(&(b)->rtmutex) #endif

@@ -339,17 +337,8 @@ ww_mutex_lock_slow_interruptible(struct

extern void ww_mutex_unlock(struct ww_mutex *lock);

-/** - * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context - * @lock: mutex to lock - * - * Trylocks a mutex without acquire context, so no deadlock detection is - * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise. - */ -static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock) -{ - return ww_mutex_base_trylock(&lock->base); -} +extern int __must_check ww_mutex_trylock(struct ww_mutex *lock, + struct ww_acquire_ctx *ctx);

/*** * ww_mutex_destroy - mark a w/w mutex unusable --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -94,6 +94,9 @@ static inline unsigned long __owner_flag return owner & MUTEX_FLAGS; }

+/* + * Returns: __mutex_owner(lock) on failure or NULL on success. + */ static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff) { unsigned long owner, curr = (unsigned long)current; @@ -736,6 +739,44 @@ __ww_mutex_lock(struct mutex *lock, unsi return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true); }

+/** + * ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context + * @ww: mutex to lock + * @ww_ctx: optional w/w acquire context + * + * Trylocks a mutex with the optional acquire context; no deadlock detection is + * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise. + * + * Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is + * specified, -EALREADY handling may happen in calls to ww_mutex_trylock. + * + * A mutex acquired with this function must be released with ww_mutex_unlock. + */ +int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx) +{ + if (!ww_ctx) + return mutex_trylock(&ww->base); + + MUTEX_WARN_ON(ww->base.magic != &ww->base); + + /* + * Reset the wounded flag after a kill. No other process can + * race and wound us here, since they can't have a valid owner + * pointer if we don't have any locks held. + */ + if (ww_ctx->acquired == 0) + ww_ctx->wounded = 0; + + if (__mutex_trylock(&ww->base)) { + ww_mutex_set_context_fastpath(ww, ww_ctx); + mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_); + return 1; + } + + return 0; +} +EXPORT_SYMBOL(ww_mutex_trylock); + #ifdef CONFIG_DEBUG_LOCK_ALLOC void __sched mutex_lock_nested(struct mutex *lock, unsigned int subclass) --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -16,6 +16,15 @@ static DEFINE_WD_CLASS(ww_class); struct workqueue_struct *wq;

+#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH +#define ww_acquire_init_noinject(a, b) do { \ + ww_acquire_init((a), (b)); \ + (a)->deadlock_inject_countdown = ~0U; \ + } while (0) +#else +#define ww_acquire_init_noinject(a, b) ww_acquire_init((a), (b)) +#endif + struct test_mutex { struct work_struct work; struct ww_mutex mutex; @@ -36,7 +45,7 @@ static void test_mutex_work(struct work_ wait_for_completion(&mtx->go);

if (mtx->flags & TEST_MTX_TRY) { - while (!ww_mutex_trylock(&mtx->mutex)) + while (!ww_mutex_trylock(&mtx->mutex, NULL)) cond_resched(); } else { ww_mutex_lock(&mtx->mutex, NULL); @@ -109,19 +118,38 @@ static int test_mutex(void) return 0; }

-static int test_aa(void) +static int test_aa(bool trylock) { struct ww_mutex mutex; struct ww_acquire_ctx ctx; int ret; + const char *from = trylock ? "trylock" : "lock";

ww_mutex_init(&mutex, &ww_class); ww_acquire_init(&ctx, &ww_class);

- ww_mutex_lock(&mutex, &ctx); + if (!trylock) { + ret = ww_mutex_lock(&mutex, &ctx); + if (ret) { + pr_err("%s: initial lock failed!\n", __func__); + goto out; + } + } else { + if (!ww_mutex_trylock(&mutex, &ctx)) { + pr_err("%s: initial trylock failed!\n", __func__); + goto out; + } + }

- if (ww_mutex_trylock(&mutex)) { - pr_err("%s: trylocked itself!\n", __func__); + if (ww_mutex_trylock(&mutex, NULL)) { + pr_err("%s: trylocked itself without context from %s!\n", __func__, from); + ww_mutex_unlock(&mutex); + ret = -EINVAL; + goto out; + } + + if (ww_mutex_trylock(&mutex, &ctx)) { + pr_err("%s: trylocked itself with context from %s!\n", __func__, from); ww_mutex_unlock(&mutex); ret = -EINVAL; goto out; @@ -129,17 +157,17 @@ static int test_aa(void)

ret = ww_mutex_lock(&mutex, &ctx); if (ret != -EALREADY) { - pr_err("%s: missed deadlock for recursing, ret=%d\n", - __func__, ret); + pr_err("%s: missed deadlock for recursing, ret=%d from %s\n", + __func__, ret, from); if (!ret) ww_mutex_unlock(&mutex); ret = -EINVAL; goto out; }

+ ww_mutex_unlock(&mutex); ret = 0; out: - ww_mutex_unlock(&mutex); ww_acquire_fini(&ctx); return ret; } @@ -150,7 +178,7 @@ struct test_abba { struct ww_mutex b_mutex; struct completion a_ready; struct completion b_ready; - bool resolve; + bool resolve, trylock; int result; };

@@ -160,8 +188,13 @@ static void test_abba_work(struct work_s struct ww_acquire_ctx ctx; int err;

- ww_acquire_init(&ctx, &ww_class); - ww_mutex_lock(&abba->b_mutex, &ctx); + ww_acquire_init_noinject(&ctx, &ww_class); + if (!abba->trylock) + ww_mutex_lock(&abba->b_mutex, &ctx); + else + WARN_ON(!ww_mutex_trylock(&abba->b_mutex, &ctx)); + + WARN_ON(READ_ONCE(abba->b_mutex.ctx) != &ctx);

complete(&abba->b_ready); wait_for_completion(&abba->a_ready); @@ -181,7 +214,7 @@ static void test_abba_work(struct work_s abba->result = err; }

-static int test_abba(bool resolve) +static int test_abba(bool trylock, bool resolve) { struct test_abba abba; struct ww_acquire_ctx ctx; @@ -192,12 +225,18 @@ static int test_abba(bool resolve) INIT_WORK_ONSTACK(&abba.work, test_abba_work); init_completion(&abba.a_ready); init_completion(&abba.b_ready); + abba.trylock = trylock; abba.resolve = resolve;

schedule_work(&abba.work);

- ww_acquire_init(&ctx, &ww_class); - ww_mutex_lock(&abba.a_mutex, &ctx); + ww_acquire_init_noinject(&ctx, &ww_class); + if (!trylock) + ww_mutex_lock(&abba.a_mutex, &ctx); + else + WARN_ON(!ww_mutex_trylock(&abba.a_mutex, &ctx)); + + WARN_ON(READ_ONCE(abba.a_mutex.ctx) != &ctx);

complete(&abba.a_ready); wait_for_completion(&abba.b_ready); @@ -249,7 +288,7 @@ static void test_cycle_work(struct work_ struct ww_acquire_ctx ctx; int err, erra = 0;

- ww_acquire_init(&ctx, &ww_class); + ww_acquire_init_noinject(&ctx, &ww_class); ww_mutex_lock(&cycle->a_mutex, &ctx);

complete(cycle->a_signal); @@ -581,7 +620,9 @@ static int stress(int nlocks, int nthrea static int __init test_ww_mutex_init(void) { int ncpus = num_online_cpus(); - int ret; + int ret, i; + + printk(KERN_INFO "Beginning ww mutex selftests\n");

wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0); if (!wq) @@ -591,17 +632,19 @@ static int __init test_ww_mutex_init(voi if (ret) return ret;

- ret = test_aa(); + ret = test_aa(false); if (ret) return ret;

- ret = test_abba(false); + ret = test_aa(true); if (ret) return ret;

- ret = test_abba(true); - if (ret) - return ret; + for (i = 0; i < 4; i++) { + ret = test_abba(i & 1, i & 2); + if (ret) + return ret; + }

ret = test_cycle(ncpus); if (ret) @@ -619,6 +662,7 @@ static int __init test_ww_mutex_init(voi if (ret) return ret;

+ printk(KERN_INFO "All ww mutex selftests passed\n"); return 0; }

--- a/kernel/locking/ww_rt_mutex.c +++ b/kernel/locking/ww_rt_mutex.c @@ -9,6 +9,31 @@ #define WW_RT #include "rtmutex.c"

+int ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx) +{ + struct rt_mutex *rtm = &lock->base; + + if (!ww_ctx) + return rt_mutex_trylock(rtm); + + /* + * Reset the wounded flag after a kill. No other process can + * race and wound us here, since they can't have a valid owner + * pointer if we don't have any locks held. + */ + if (ww_ctx->acquired == 0) + ww_ctx->wounded = 0; + + if (__rt_mutex_trylock(&rtm->rtmutex)) { + ww_mutex_set_context_fastpath(lock, ww_ctx); + mutex_acquire_nest(&rtm->dep_map, 0, 1, ww_ctx->dep_map, _RET_IP_); + return 1; + } + + return 0; +} +EXPORT_SYMBOL(ww_mutex_trylock); + static int __sched __ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx, unsigned int state, unsigned long ip) --- a/lib/locking-selftest.c +++ b/lib/locking-selftest.c @@ -258,7 +258,7 @@ static void init_shared_classes(void) #define WWAF(x) ww_acquire_fini(x)

#define WWL(x, c) ww_mutex_lock(x, c) -#define WWT(x) ww_mutex_trylock(x) +#define WWT(x) ww_mutex_trylock(x, NULL) #define WWL1(x) ww_mutex_lock(x, NULL) #define WWU(x) ww_mutex_unlock(x)

On Tue, Sep 14, 2021 at 02:43:02PM +0200, Maarten Lankhorst wrote:

Op 14-09-2021 om 08:50 schreef Peter Zijlstra:

...

On Mon, Sep 13, 2021 at 10:42:36AM +0200, Maarten Lankhorst wrote:

...

...

+/**

• • ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
• • @ww: mutex to lock
• • @ww_ctx: optional w/w acquire context
• • Trylocks a mutex with the optional acquire context; no deadlock detection is
• • possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
• • Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
• • specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
• • A mutex acquired with this function must be released with ww_mutex_unlock.
• */

+int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx) +{

• if (!ww_ctx)

• return mutex_trylock(&ww->base);
  

• MUTEX_WARN_ON(ww->base.magic != &ww->base);
• if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))

• return -EALREADY;
  

I'm not 100% sure this is a good idea, because it would make the trylock weird. For i915 I checked manually, because I didn't want to change the function signature. This is probably the other extreme.

"if (ww_mutex_trylock())" would look correct, but actually be wrong and lead to double unlock without adjustments. Maybe we could make a ww_mutex_trylock_ctx_err, which would return -EALREADY or -EBUSY on failure, and 0 on success? We could keep ww_mutex_trylock without ctx, probably just #define as (!ww_mutex_trylock_ctx_err(lock, NULL))

Urgh, yeah. Also, I suppose that if we already own it, we'll just fail the trylock anyway. Let me take this out.

...

...

• /*

• * Reset the wounded flag after a kill. No other process can
  

• * race and wound us here, since they can't have a valid owner
  

• * pointer if we don't have any locks held.
  

• */
  

• if (ww_ctx->acquired == 0)

• ww_ctx->wounded = 0;
  

Yeah I guess this needs fixing too. Not completely sure since trylock wouldn't do the whole ww dance, but since it's our first lock, probably best to do so regardless so other users don't trip over it.

This is actually critical, because if this trylock is the first lock acquisition for the context, there won't be any other opportunity to reset this value.

...

...

• if (__mutex_trylock(&ww->base)) {

• ww_mutex_set_context_fastpath(ww, ww_ctx);
  

• mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
  

• return 1;
  

• }
• return 0;

+} +EXPORT_SYMBOL(ww_mutex_trylock);

Updated version below...

---

Subject: kernel/locking: Add context to ww_mutex_trylock() From: Maarten Lankhorst maarten.lankhorst@linux.intel.com Date: Thu, 9 Sep 2021 11:32:18 +0200

From: Maarten Lankhorst maarten.lankhorst@linux.intel.com

i915 will soon gain an eviction path that trylock a whole lot of locks for eviction, getting dmesg failures like below:

BUG: MAX_LOCK_DEPTH too low! turning off the locking correctness validator. depth: 48 max: 48! 48 locks held by i915_selftest/5776: #0: ffff888101a79240 (&dev->mutex){....}-{3:3}, at: __driver_attach+0x88/0x160 #1: ffffc900009778c0 (reservation_ww_class_acquire){+.+.}-{0:0}, at: i915_vma_pin.constprop.63+0x39/0x1b0 [i915] #2: ffff88800cf74de8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_vma_pin.constprop.63+0x5f/0x1b0 [i915] #3: ffff88810c7f9e38 (&vm->mutex/1){+.+.}-{3:3}, at: i915_vma_pin_ww+0x1c4/0x9d0 [i915] #4: ffff88810bad5768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #5: ffff88810bad60e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] ... #46: ffff88811964d768 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] #47: ffff88811964e0e8 (reservation_ww_class_mutex){+.+.}-{3:3}, at: i915_gem_evict_something+0x110/0x860 [i915] INFO: lockdep is turned off.

Fixing eviction to nest into ww_class_acquire is a high priority, but it requires a rework of the entire driver, which can only be done one step at a time.

As an intermediate solution, add an acquire context to ww_mutex_trylock, which allows us to do proper nesting annotations on the trylocks, making the above lockdep splat disappear.

This is also useful in regulator_lock_nested, which may avoid dropping regulator_nesting_mutex in the uncontended path, so use it there.

TTM may be another user for this, where we could lock a buffer in a fastpath with list locks held, without dropping all locks we hold.

[peterz: rework actual ww_mutex_trylock() implementations] Signed-off-by: Maarten Lankhorst maarten.lankhorst@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org

---

My original patch series with this patch in place still passes i915 selftests, looks good to me. :)

For merge logistics, can we pls have a stable branch? I expect that the i915 patches will be ready for 5.16.

Or send it in for -rc2 so that the interface change doesn't cause needless conflicts, whatever you think is best. -Daniel

Feel free to apply.

...

drivers/gpu/drm/drm_modeset_lock.c | 2 drivers/regulator/core.c | 2 include/linux/dma-resv.h | 2 include/linux/ww_mutex.h | 15 ------ kernel/locking/mutex.c | 41 +++++++++++++++++ kernel/locking/test-ww_mutex.c | 86 +++++++++++++++++++++++++++---------- kernel/locking/ww_rt_mutex.c | 25 ++++++++++ lib/locking-selftest.c | 2 8 files changed, 137 insertions(+), 38 deletions(-)

--- a/drivers/gpu/drm/drm_modeset_lock.c +++ b/drivers/gpu/drm/drm_modeset_lock.c @@ -248,7 +248,7 @@ static inline int modeset_lock(struct dr if (ctx->trylock_only) { lockdep_assert_held(&ctx->ww_ctx);

• if (!ww_mutex_trylock(&lock->mutex))
  

• if (!ww_mutex_trylock(&lock->mutex, NULL))
  return -EBUSY;
  

  else return 0;

--- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -145,7 +145,7 @@ static inline int regulator_lock_nested(

mutex_lock(&regulator_nesting_mutex);

• if (ww_ctx || !ww_mutex_trylock(&rdev->mutex)) {

• if (!ww_mutex_trylock(&rdev->mutex, ww_ctx)) { if (rdev->mutex_owner == current) rdev->ref_cnt++; else

--- a/include/linux/dma-resv.h +++ b/include/linux/dma-resv.h @@ -173,7 +173,7 @@ static inline int dma_resv_lock_slow_int */ static inline bool __must_check dma_resv_trylock(struct dma_resv *obj) {

• return ww_mutex_trylock(&obj->lock);

• return ww_mutex_trylock(&obj->lock, NULL);

}

/** --- a/include/linux/ww_mutex.h +++ b/include/linux/ww_mutex.h @@ -28,12 +28,10 @@ #ifndef CONFIG_PREEMPT_RT #define WW_MUTEX_BASE mutex #define ww_mutex_base_init(l,n,k) __mutex_init(l,n,k) -#define ww_mutex_base_trylock(l) mutex_trylock(l) #define ww_mutex_base_is_locked(b) mutex_is_locked((b)) #else #define WW_MUTEX_BASE rt_mutex #define ww_mutex_base_init(l,n,k) __rt_mutex_init(l,n,k) -#define ww_mutex_base_trylock(l) rt_mutex_trylock(l) #define ww_mutex_base_is_locked(b) rt_mutex_base_is_locked(&(b)->rtmutex) #endif

@@ -339,17 +337,8 @@ ww_mutex_lock_slow_interruptible(struct

extern void ww_mutex_unlock(struct ww_mutex *lock);

-/**

• • ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
• • @lock: mutex to lock
• • Trylocks a mutex without acquire context, so no deadlock detection is
• • possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
• */

-static inline int __must_check ww_mutex_trylock(struct ww_mutex *lock) -{

• return ww_mutex_base_trylock(&lock->base);

-} +extern int __must_check ww_mutex_trylock(struct ww_mutex *lock,

• 			 struct ww_acquire_ctx *ctx);
  
  

/***

• ww_mutex_destroy - mark a w/w mutex unusable

--- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -94,6 +94,9 @@ static inline unsigned long __owner_flag return owner & MUTEX_FLAGS; }

+/*

• • Returns: __mutex_owner(lock) on failure or NULL on success.
• */

static inline struct task_struct *__mutex_trylock_common(struct mutex *lock, bool handoff) { unsigned long owner, curr = (unsigned long)current; @@ -736,6 +739,44 @@ __ww_mutex_lock(struct mutex *lock, unsi return __mutex_lock_common(lock, state, subclass, NULL, ip, ww_ctx, true); }

+/**

• • ww_mutex_trylock - tries to acquire the w/w mutex with optional acquire context
• • @ww: mutex to lock
• • @ww_ctx: optional w/w acquire context
• • Trylocks a mutex with the optional acquire context; no deadlock detection is
• • possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
• • Unlike ww_mutex_lock, no deadlock handling is performed. However, if a @ctx is
• • specified, -EALREADY handling may happen in calls to ww_mutex_trylock.
• • A mutex acquired with this function must be released with ww_mutex_unlock.
• */

+int ww_mutex_trylock(struct ww_mutex *ww, struct ww_acquire_ctx *ww_ctx) +{

• if (!ww_ctx)

• return mutex_trylock(&ww->base);
  

• MUTEX_WARN_ON(ww->base.magic != &ww->base);
• /*

• * Reset the wounded flag after a kill. No other process can
  

• * race and wound us here, since they can't have a valid owner
  

• * pointer if we don't have any locks held.
  

• */
  

• if (ww_ctx->acquired == 0)

• ww_ctx->wounded = 0;
  

• if (__mutex_trylock(&ww->base)) {

• ww_mutex_set_context_fastpath(ww, ww_ctx);
  

• mutex_acquire_nest(&ww->base.dep_map, 0, 1, &ww_ctx->dep_map, _RET_IP_);
  

• return 1;
  

• }
• return 0;

+} +EXPORT_SYMBOL(ww_mutex_trylock);

#ifdef CONFIG_DEBUG_LOCK_ALLOC void __sched mutex_lock_nested(struct mutex *lock, unsigned int subclass) --- a/kernel/locking/test-ww_mutex.c +++ b/kernel/locking/test-ww_mutex.c @@ -16,6 +16,15 @@ static DEFINE_WD_CLASS(ww_class); struct workqueue_struct *wq;

+#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH +#define ww_acquire_init_noinject(a, b) do { \

• ww_acquire_init((a), (b)); \
  

• (a)->deadlock_inject_countdown = ~0U; \
  

• } while (0)

+#else +#define ww_acquire_init_noinject(a, b) ww_acquire_init((a), (b)) +#endif

struct test_mutex { struct work_struct work; struct ww_mutex mutex; @@ -36,7 +45,7 @@ static void test_mutex_work(struct work_ wait_for_completion(&mtx->go);

if (mtx->flags & TEST_MTX_TRY) {

• while (!ww_mutex_trylock(&mtx->mutex))
  

• while (!ww_mutex_trylock(&mtx->mutex, NULL))
  cond_resched();
  

  } else { ww_mutex_lock(&mtx->mutex, NULL);

@@ -109,19 +118,38 @@ static int test_mutex(void) return 0; }

-static int test_aa(void) +static int test_aa(bool trylock) { struct ww_mutex mutex; struct ww_acquire_ctx ctx; int ret;

• const char *from = trylock ? "trylock" : "lock";

  ww_mutex_init(&mutex, &ww_class); ww_acquire_init(&ctx, &ww_class);

• ww_mutex_lock(&mutex, &ctx);

• if (!trylock) {

• ret = ww_mutex_lock(&mutex, &ctx);
  

• if (ret) {
  

• 	pr_err("%s: initial lock failed!\n", __func__);
  

• 	goto out;
  

• }
  

• } else {

• if (!ww_mutex_trylock(&mutex, &ctx)) {
  

• 	pr_err("%s: initial trylock failed!\n", __func__);
  

• 	goto out;
  

• }
  

• }

• if (ww_mutex_trylock(&mutex)) {

• pr_err("%s: trylocked itself!\n", __func__);
  

• if (ww_mutex_trylock(&mutex, NULL)) {

• pr_err("%s: trylocked itself without context from %s!\n", __func__, from);
  

• ww_mutex_unlock(&mutex);
  

• ret = -EINVAL;
  

• goto out;
  

• }
• if (ww_mutex_trylock(&mutex, &ctx)) {

• pr_err("%s: trylocked itself with context from %s!\n", __func__, from);
  

  ww_mutex_unlock(&mutex); ret = -EINVAL; goto out;

@@ -129,17 +157,17 @@ static int test_aa(void)

ret = ww_mutex_lock(&mutex, &ctx); if (ret != -EALREADY) {

• pr_err("%s: missed deadlock for recursing, ret=%d\n",
  

•        __func__, ret);
  

• pr_err("%s: missed deadlock for recursing, ret=%d from %s\n",
  

•        __func__, ret, from);
  

  if (!ret) ww_mutex_unlock(&mutex); ret = -EINVAL; goto out; }

• ww_mutex_unlock(&mutex); ret = 0;

out:

• ww_mutex_unlock(&mutex); ww_acquire_fini(&ctx); return ret;

} @@ -150,7 +178,7 @@ struct test_abba { struct ww_mutex b_mutex; struct completion a_ready; struct completion b_ready;

• bool resolve;

• bool resolve, trylock; int result;

};

@@ -160,8 +188,13 @@ static void test_abba_work(struct work_s struct ww_acquire_ctx ctx; int err;

• ww_acquire_init(&ctx, &ww_class);
• ww_mutex_lock(&abba->b_mutex, &ctx);

• ww_acquire_init_noinject(&ctx, &ww_class);

• if (!abba->trylock)

• ww_mutex_lock(&abba->b_mutex, &ctx);
  

• else

• WARN_ON(!ww_mutex_trylock(&abba->b_mutex, &ctx));
  

• WARN_ON(READ_ONCE(abba->b_mutex.ctx) != &ctx);

  complete(&abba->b_ready); wait_for_completion(&abba->a_ready);

@@ -181,7 +214,7 @@ static void test_abba_work(struct work_s abba->result = err; }

-static int test_abba(bool resolve) +static int test_abba(bool trylock, bool resolve) { struct test_abba abba; struct ww_acquire_ctx ctx; @@ -192,12 +225,18 @@ static int test_abba(bool resolve) INIT_WORK_ONSTACK(&abba.work, test_abba_work); init_completion(&abba.a_ready); init_completion(&abba.b_ready);

• abba.trylock = trylock; abba.resolve = resolve;

  schedule_work(&abba.work);

• ww_acquire_init(&ctx, &ww_class);
• ww_mutex_lock(&abba.a_mutex, &ctx);

• ww_acquire_init_noinject(&ctx, &ww_class);

• if (!trylock)

• ww_mutex_lock(&abba.a_mutex, &ctx);
  

• else

• WARN_ON(!ww_mutex_trylock(&abba.a_mutex, &ctx));
  

• WARN_ON(READ_ONCE(abba.a_mutex.ctx) != &ctx);

  complete(&abba.a_ready); wait_for_completion(&abba.b_ready);

@@ -249,7 +288,7 @@ static void test_cycle_work(struct work_ struct ww_acquire_ctx ctx; int err, erra = 0;

• ww_acquire_init(&ctx, &ww_class);

• ww_acquire_init_noinject(&ctx, &ww_class); ww_mutex_lock(&cycle->a_mutex, &ctx);

  complete(cycle->a_signal);

@@ -581,7 +620,9 @@ static int stress(int nlocks, int nthrea static int __init test_ww_mutex_init(void) { int ncpus = num_online_cpus();

• int ret;

• int ret, i;

• printk(KERN_INFO "Beginning ww mutex selftests\n");

  wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0); if (!wq)

@@ -591,17 +632,19 @@ static int __init test_ww_mutex_init(voi if (ret) return ret;

• ret = test_aa();

• ret = test_aa(false); if (ret) return ret;

• ret = test_abba(false);

• ret = test_aa(true); if (ret) return ret;

• ret = test_abba(true);
• if (ret)

• return ret;
  

• for (i = 0; i < 4; i++) {

• ret = test_abba(i & 1, i & 2);
  

• if (ret)
  

• 	return ret;
  

• }

  ret = test_cycle(ncpus); if (ret)

@@ -619,6 +662,7 @@ static int __init test_ww_mutex_init(voi if (ret) return ret;

• printk(KERN_INFO "All ww mutex selftests passed\n"); return 0;

}

--- a/kernel/locking/ww_rt_mutex.c +++ b/kernel/locking/ww_rt_mutex.c @@ -9,6 +9,31 @@ #define WW_RT #include "rtmutex.c"

+int ww_mutex_trylock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx) +{

• struct rt_mutex *rtm = &lock->base;
• if (!ww_ctx)

• return rt_mutex_trylock(rtm);
  

• /*

• * Reset the wounded flag after a kill. No other process can
  

• * race and wound us here, since they can't have a valid owner
  

• * pointer if we don't have any locks held.
  

• */
  

• if (ww_ctx->acquired == 0)

• ww_ctx->wounded = 0;
  

• if (__rt_mutex_trylock(&rtm->rtmutex)) {

• ww_mutex_set_context_fastpath(lock, ww_ctx);
  

• mutex_acquire_nest(&rtm->dep_map, 0, 1, ww_ctx->dep_map, _RET_IP_);
  

• return 1;
  

• }
• return 0;

+} +EXPORT_SYMBOL(ww_mutex_trylock);

static int __sched __ww_rt_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx, unsigned int state, unsigned long ip) --- a/lib/locking-selftest.c +++ b/lib/locking-selftest.c @@ -258,7 +258,7 @@ static void init_shared_classes(void) #define WWAF(x) ww_acquire_fini(x)

#define WWL(x, c) ww_mutex_lock(x, c) -#define WWT(x) ww_mutex_trylock(x) +#define WWT(x) ww_mutex_trylock(x, NULL) #define WWL1(x) ww_mutex_lock(x, NULL) #define WWU(x) ww_mutex_unlock(x)