fs_reclaim_acquire/release nicely catch recursion issues when allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend to use to keep the excessive caches in check). For mmu notifier recursions we do have lockdep annotations since 23b68395c7c7 ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end").

But these only fire if a path actually results in some pte invalidation - for most small allocations that's very rarely the case. The other trouble is that pte invalidation can happen any time when __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe choice, GFP_NOIO isn't good enough to avoid potential mmu notifier recursion.

I was pondering whether we should just do the general annotation, but there's always the risk for false positives. Plus I'm assuming that the core fs and io code is a lot better reviewed and tested than random mmu notifier code in drivers. Hence why I decide to only annotate for that specific case.

Furthermore even if we'd create a lockdep map for direct reclaim, we'd still need to explicit pull in the mmu notifier map - there's a lot more places that do pte invalidation than just direct reclaim, these two contexts arent the same.

Note that the mmu notifiers needing their own independent lockdep map is also the reason we can't hold them from fs_reclaim_acquire to fs_reclaim_release - it would nest with the acquistion in the pte invalidation code, causing a lockdep splat. And we can't remove the annotations from pte invalidation and all the other places since they're called from many other places than page reclaim. Hence we can only do the equivalent of might_lock, but on the raw lockdep map.

With this we can also remove the lockdep priming added in 66204f1d2d1b ("mm/mmu_notifiers: prime lockdep") since the new annotations are strictly more powerful.

v2: Review from Thomas Hellstrom: - unbotch the fs_reclaim context check, I accidentally inverted it, but it didn't blow up because I inverted it immediately - fix compiling for !CONFIG_MMU_NOTIFIER

v3: Unbreak the PF_MEMALLOC_ context flags. Thanks to Qian for the report and Dave for explaining what I failed to see.

Reviewed-by: Jason Gunthorpe jgg@nvidia.com Cc: linux-fsdevel@vger.kernel.org Cc: Dave Chinner david@fromorbit.com Cc: Qian Cai cai@lca.pw Cc: linux-xfs@vger.kernel.org Cc: Thomas Hellström (Intel) thomas_os@shipmail.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Jason Gunthorpe jgg@mellanox.com Cc: linux-mm@kvack.org Cc: linux-rdma@vger.kernel.org Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Christian König christian.koenig@amd.com Cc: "Matthew Wilcox (Oracle)" willy@infradead.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com --- mm/mmu_notifier.c | 7 ------- mm/page_alloc.c | 31 ++++++++++++++++++++----------- 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c index 5654dd19addc..61ee40ed804e 100644 --- a/mm/mmu_notifier.c +++ b/mm/mmu_notifier.c @@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription, mmap_assert_write_locked(mm); BUG_ON(atomic_read(&mm->mm_users) <= 0);

- if (IS_ENABLED(CONFIG_LOCKDEP)) { - fs_reclaim_acquire(GFP_KERNEL); - lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); - lock_map_release(&__mmu_notifier_invalidate_range_start_map); - fs_reclaim_release(GFP_KERNEL); - } - if (!mm->notifier_subscriptions) { /* * kmalloc cannot be called under mm_take_all_locks(), but we diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 23f5066bd4a5..ff0f9a84b8de 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -57,6 +57,7 @@ #include <trace/events/oom.h> #include <linux/prefetch.h> #include <linux/mm_inline.h> +#include <linux/mmu_notifier.h> #include <linux/migrate.h> #include <linux/hugetlb.h> #include <linux/sched/rt.h> @@ -4264,10 +4265,8 @@ should_compact_retry(struct alloc_context *ac, unsigned int order, int alloc_fla static struct lockdep_map __fs_reclaim_map = STATIC_LOCKDEP_MAP_INIT("fs_reclaim", &__fs_reclaim_map);

-static bool __need_fs_reclaim(gfp_t gfp_mask) +static bool __need_reclaim(gfp_t gfp_mask) { - gfp_mask = current_gfp_context(gfp_mask); - /* no reclaim without waiting on it */ if (!(gfp_mask & __GFP_DIRECT_RECLAIM)) return false; @@ -4276,10 +4275,6 @@ static bool __need_fs_reclaim(gfp_t gfp_mask) if (current->flags & PF_MEMALLOC) return false;

- /* We're only interested __GFP_FS allocations for now */ - if (!(gfp_mask & __GFP_FS)) - return false; - if (gfp_mask & __GFP_NOLOCKDEP) return false;

@@ -4298,15 +4293,29 @@ void __fs_reclaim_release(void)

void fs_reclaim_acquire(gfp_t gfp_mask) { - if (__need_fs_reclaim(gfp_mask)) - __fs_reclaim_acquire(); + gfp_mask = current_gfp_context(gfp_mask); + + if (__need_reclaim(gfp_mask)) { + if (gfp_mask & __GFP_FS) + __fs_reclaim_acquire(); + +#ifdef CONFIG_MMU_NOTIFIER + lock_map_acquire(&__mmu_notifier_invalidate_range_start_map); + lock_map_release(&__mmu_notifier_invalidate_range_start_map); +#endif + + } } EXPORT_SYMBOL_GPL(fs_reclaim_acquire);

void fs_reclaim_release(gfp_t gfp_mask) { - if (__need_fs_reclaim(gfp_mask)) - __fs_reclaim_release(); + gfp_mask = current_gfp_context(gfp_mask); + + if (__need_reclaim(gfp_mask)) { + if (gfp_mask & __GFP_FS) + __fs_reclaim_release(); + } } EXPORT_SYMBOL_GPL(fs_reclaim_release); #endif

Since I butchered this I figured better to make sure we have testcases for this now. Since we only have a locking context for __GFP_FS that's the only thing we're testing right now.

Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: linux-fsdevel@vger.kernel.org Cc: Dave Chinner david@fromorbit.com Cc: Qian Cai cai@lca.pw Cc: linux-xfs@vger.kernel.org Cc: Thomas Hellström (Intel) thomas_os@shipmail.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Jason Gunthorpe jgg@mellanox.com Cc: linux-mm@kvack.org Cc: linux-rdma@vger.kernel.org Cc: Maarten Lankhorst maarten.lankhorst@linux.intel.com Cc: Christian König christian.koenig@amd.com Cc: "Matthew Wilcox (Oracle)" willy@infradead.org Signed-off-by: Daniel Vetter daniel.vetter@intel.com Cc: Peter Zijlstra peterz@infradead.org Cc: Ingo Molnar mingo@redhat.com Cc: Will Deacon will@kernel.org Cc: linux-kernel@vger.kernel.org --- lib/locking-selftest.c | 47 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c index a899b3f0e2e5..ad47c3358e30 100644 --- a/lib/locking-selftest.c +++ b/lib/locking-selftest.c @@ -15,6 +15,7 @@ #include <linux/mutex.h> #include <linux/ww_mutex.h> #include <linux/sched.h> +#include <linux/sched/mm.h> #include <linux/delay.h> #include <linux/lockdep.h> #include <linux/spinlock.h> @@ -2357,6 +2358,50 @@ static void queued_read_lock_tests(void) pr_cont("\n"); }

+static void fs_reclaim_correct_nesting(void) +{ + fs_reclaim_acquire(GFP_KERNEL); + might_alloc(GFP_NOFS); + fs_reclaim_release(GFP_KERNEL); +} + +static void fs_reclaim_wrong_nesting(void) +{ + fs_reclaim_acquire(GFP_KERNEL); + might_alloc(GFP_KERNEL); + fs_reclaim_release(GFP_KERNEL); +} + +static void fs_reclaim_protected_nesting(void) +{ + unsigned int flags; + + fs_reclaim_acquire(GFP_KERNEL); + flags = memalloc_nofs_save(); + might_alloc(GFP_KERNEL); + memalloc_nofs_restore(flags); + fs_reclaim_release(GFP_KERNEL); +} + +static void fs_reclaim_tests(void) +{ + printk(" --------------------\n"); + printk(" | fs_reclaim tests |\n"); + printk(" --------------------\n"); + + print_testname("correct nesting"); + dotest(fs_reclaim_correct_nesting, SUCCESS, 0); + pr_cont("\n"); + + print_testname("wrong nesting"); + dotest(fs_reclaim_wrong_nesting, FAILURE, 0); + pr_cont("\n"); + + print_testname("protected nesting"); + dotest(fs_reclaim_protected_nesting, SUCCESS, 0); + pr_cont("\n"); +} + void locking_selftest(void) { /* @@ -2478,6 +2523,8 @@ void locking_selftest(void) if (IS_ENABLED(CONFIG_QUEUED_RWLOCKS)) queued_read_lock_tests();

+ fs_reclaim_tests(); + if (unexpected_testcase_failures) { printk("-----------------------------------------------------------------\n"); debug_locks = 0;