From: Nicolai Hähnle Nicolai.Haehnle@amd.com

We will add a new field to struct mutex_waiter. This field must be initialized for all waiters if any waiter uses the ww_use_ctx path.

So there is a trade-off: Keep ww_mutex locking without a context on the faster non-use_ww_ctx path, at the cost of adding the initialization to all mutex locks (including non-ww_mutexes), or avoid the additional cost for non-ww_mutex locks, at the cost of adding additional checks to the use_ww_ctx path.

We take the latter choice. It may be worth eliminating the users of ww_mutex_lock(lock, NULL), but there are a lot of them.

Move the declaration of ww in __mutex_lock_common closer to its uses because gcc otherwise (incorrectly) believes ww may be used without initialization.

Cc: Peter Zijlstra peterz@infradead.org Cc: Ingo Molnar mingo@redhat.com Cc: Maarten Lankhorst dev@mblankhorst.nl Cc: Daniel Vetter daniel@ffwll.ch Cc: Chris Wilson chris@chris-wilson.co.uk Cc: dri-devel@lists.freedesktop.org Signed-off-by: Nicolai Hähnle Nicolai.Haehnle@amd.com --- include/linux/ww_mutex.h | 11 ++--------- kernel/locking/mutex.c | 37 +++++++++++++++++++++++++------------ 2 files changed, 27 insertions(+), 21 deletions(-)

diff --git a/include/linux/ww_mutex.h b/include/linux/ww_mutex.h index 2bb5deb..a5960e5 100644 --- a/include/linux/ww_mutex.h +++ b/include/linux/ww_mutex.h @@ -222,11 +222,7 @@ extern int __must_check __ww_mutex_lock_interruptible(struct ww_mutex *lock, */ static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { - if (ctx) - return __ww_mutex_lock(lock, ctx); - - mutex_lock(&lock->base); - return 0; + return __ww_mutex_lock(lock, ctx); }

/** @@ -262,10 +258,7 @@ static inline int ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ct static inline int __must_check ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) { - if (ctx) - return __ww_mutex_lock_interruptible(lock, ctx); - else - return mutex_lock_interruptible(&lock->base); + return __ww_mutex_lock_interruptible(lock, ctx); }

/** diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 200629a..585627f 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -381,7 +381,7 @@ bool mutex_spin_on_owner(struct mutex *lock, struct task_struct *owner, break; }

- if (use_ww_ctx && ww_ctx->acquired > 0) { + if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) { struct ww_mutex *ww;

ww = container_of(lock, struct ww_mutex, base); @@ -640,10 +640,11 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, struct mutex_waiter waiter; unsigned long flags; bool first = false; - struct ww_mutex *ww; int ret;

- if (use_ww_ctx) { + if (use_ww_ctx && ww_ctx) { + struct ww_mutex *ww; + ww = container_of(lock, struct ww_mutex, base); if (unlikely(ww_ctx == READ_ONCE(ww->ctx))) return -EALREADY; @@ -656,8 +657,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, mutex_optimistic_spin(lock, ww_ctx, use_ww_ctx, false)) { /* got the lock, yay! */ lock_acquired(&lock->dep_map, ip); - if (use_ww_ctx) + if (use_ww_ctx && ww_ctx) { + struct ww_mutex *ww; + + ww = container_of(lock, struct ww_mutex, base); ww_mutex_set_context_fastpath(ww, ww_ctx); + } preempt_enable(); return 0; } @@ -702,7 +707,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, goto err; }

- if (use_ww_ctx && ww_ctx->acquired > 0) { + if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) { ret = __ww_mutex_lock_check_stamp(lock, ww_ctx); if (ret) goto err; @@ -742,8 +747,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, /* got the lock - cleanup and rejoice! */ lock_acquired(&lock->dep_map, ip);

- if (use_ww_ctx) + if (use_ww_ctx && ww_ctx) { + struct ww_mutex *ww; + + ww = container_of(lock, struct ww_mutex, base); ww_mutex_set_context_slowpath(ww, ww_ctx); + }

spin_unlock_mutex(&lock->wait_lock, flags); preempt_enable(); @@ -830,8 +839,9 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

might_sleep(); ret = __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE, - 0, &ctx->dep_map, _RET_IP_, ctx, 1); - if (!ret && ctx->acquired > 1) + 0, ctx ? &ctx->dep_map : NULL, _RET_IP_, + ctx, 1); + if (!ret && ctx && ctx->acquired > 1) return ww_mutex_deadlock_injection(lock, ctx);

return ret; @@ -845,9 +855,10 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)

might_sleep(); ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE, - 0, &ctx->dep_map, _RET_IP_, ctx, 1); + 0, ctx ? &ctx->dep_map : NULL, _RET_IP_, + ctx, 1);

- if (!ret && ctx->acquired > 1) + if (!ret && ctx && ctx->acquired > 1) return ww_mutex_deadlock_injection(lock, ctx);

return ret; @@ -1034,7 +1045,8 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) might_sleep();

if (__mutex_trylock_fast(&lock->base)) { - ww_mutex_set_context_fastpath(lock, ctx); + if (ctx) + ww_mutex_set_context_fastpath(lock, ctx); return 0; }

@@ -1048,7 +1060,8 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx) might_sleep();

if (__mutex_trylock_fast(&lock->base)) { - ww_mutex_set_context_fastpath(lock, ctx); + if (ctx) + ww_mutex_set_context_fastpath(lock, ctx); return 0; }