[PATCH 01/18] mm: Track mmu notifiers in fs_reclaim_acquire/release

Daniel Vetter daniel.vetter at ffwll.ch
Thu Jun 4 08:12:07 UTC 2020

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

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.

Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Jason Gunthorpe <jgg at mellanox.com>
Cc: linux-mm at kvack.org
Cc: linux-rdma at vger.kernel.org
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Christian König <christian.koenig at amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
This is part of a gpu lockdep annotation series simply because it
really helps to catch issues where gpu subsystem locks and primitives
can deadlock with themselves through allocations and mmu notifiers.
But aside from that motivation it should be completely free-standing,
and can land through -mm/-rdma/-hmm or any other tree really whenever.
 mm/mmu_notifier.c |  7 -------
 mm/page_alloc.c   | 23 ++++++++++++++---------
 2 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 06852b896fa6..5d578b9122f8 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -612,13 +612,6 @@ int __mmu_notifier_register(struct mmu_notifier *subscription,
 	BUG_ON(atomic_read(&mm->mm_users) <= 0);
-		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 13cc653122b7..f8a222db4a53 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>
@@ -4124,7 +4125,7 @@ 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);
@@ -4136,10 +4137,6 @@ 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;
@@ -4158,15 +4155,23 @@ void __fs_reclaim_release(void)
 void fs_reclaim_acquire(gfp_t gfp_mask)
-	if (__need_fs_reclaim(gfp_mask))
-		__fs_reclaim_acquire();
+	if (__need_reclaim(gfp_mask)) {
+		if (!(gfp_mask & __GFP_FS))
+			__fs_reclaim_acquire();
+		lock_map_acquire(&__mmu_notifier_invalidate_range_start_map);
+		lock_map_release(&__mmu_notifier_invalidate_range_start_map);
+	}
 void fs_reclaim_release(gfp_t gfp_mask)
-	if (__need_fs_reclaim(gfp_mask))
-		__fs_reclaim_release();
+	if (__need_reclaim(gfp_mask)) {
+		if (!(gfp_mask & __GFP_FS))
+			__fs_reclaim_release();
+	}

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