[Devel] [PATCH rh7] mm: fix false positive WARN on fs reenterence

[Andrey Ryabinin]

If PF_MEMALLOC flag set allocation with __GFP_FS cannot enter
into fs layer because PF_MEMALLOC forbids direct reclaim.

E.g. zswap_frontswap_store() uses GFP_KERNEL and called during
reclaim possibly in NOFS, but __GFP_FS is fine because PF_MEMALLOC
protects us from deadlock.

WARNING: at mm/slub.c:1250 slab_pre_alloc_hook.isra.42.part.43+0x15/0x17()
...
 Call Trace:
 [<ffffffff8163413f>] dump_stack+0x19/0x1b
 [<ffffffff8107b620>] warn_slowpath_common+0x70/0xb0
 [<ffffffff8107b76a>] warn_slowpath_null+0x1a/0x20
 [<ffffffff816311c8>] slab_pre_alloc_hook.isra.42.part.43+0x15/0x17
 [<ffffffff811d7235>] kmem_cache_alloc+0x55/0x220
 [<ffffffff811c4a09>] zswap_frontswap_store+0xe9/0x320
 [<ffffffff811c3d5b>] __frontswap_store+0x7b/0x110
 [<ffffffff811bf6a3>] swap_writepage+0x23/0x80
 [<ffffffff8118fff2>] shrink_page_list+0x4b2/0xa80
 [<ffffffff81190c1b>] shrink_inactive_list+0x1fb/0x6c0
 [<ffffffff811918b5>] shrink_lruvec+0x395/0x800
 [<ffffffff81191e0f>] shrink_zone+0xef/0x2d0
 [<ffffffff81192390>] do_try_to_free_pages+0x170/0x530
 [<ffffffff81192825>] try_to_free_pages+0xd5/0x160
 [<ffffffff81185aa5>] __alloc_pages_nodemask+0x8a5/0xc10
 [<ffffffff811cb1da>] alloc_pages_current+0xaa/0x170
 [<ffffffff811803de>] __get_free_pages+0xe/0x50
 [<ffffffffa029a5aa>] jbd2_alloc+0x8a/0x90 [jbd2]
 [<ffffffffa028fab4>] do_get_write_access+0x1d4/0x4d0 [jbd2]
 [<ffffffffa028fdd7>] jbd2_journal_get_write_access+0x27/0x40 [jbd2]
 [<ffffffffa02e8e0b>] __ext4_journal_get_write_access+0x3b/0x80 [ext4]
 [<ffffffffa02efccd>] ext4_mb_mark_diskspace_used+0x7d/0x4f0 [ext4]
 [<ffffffffa02f156d>] ext4_mb_new_blocks+0x36d/0x620 [ext4]
 [<ffffffffa02e601d>] ext4_ext_map_blocks+0x49d/0xed0 [ext4]
 [<ffffffffa02b2689>] ext4_map_blocks+0x179/0x590 [ext4]
 [<ffffffffa02b5bc2>] ext4_writepages+0x692/0xd60 [ext4]
 [<ffffffff8118828e>] do_writepages+0x1e/0x40

With this commit d89e689bd0e8 ("mm/zswap: fix potential deadlock in zswap_frontswap_store()")
is no longer required and can be reverted.

Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/page_alloc.c | 3 ++-
 mm/slab.c       | 6 ++++--
 mm/slub.c       | 3 ++-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index afac33e..2607756 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3155,7 +3155,8 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
 	lockdep_trace_alloc(gfp_mask);
 
 	might_sleep_if(gfp_mask & __GFP_WAIT);
-	WARN_ON_ONCE((gfp_mask & __GFP_FS) && current->journal_info);
+	WARN_ON_ONCE((gfp_mask & __GFP_FS) && current->journal_info &&
+		!(current->flags & PF_MEMALLOC));
 
 	if (should_fail_alloc_page(gfp_mask, order))
 		return NULL;
diff --git a/mm/slab.c b/mm/slab.c
index 4f0c22e..74944fe 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3343,7 +3343,8 @@ slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid,
 	flags &= gfp_allowed_mask;
 
 	lockdep_trace_alloc(flags);
-	WARN_ON_ONCE((flags & __GFP_FS) && current->journal_info);
+	WARN_ON_ONCE((flags & __GFP_FS) && current->journal_info &&
+		!(current->flags & PF_MEMALLOC));
 
 	if (slab_should_failslab(cachep, flags))
 		return NULL;
@@ -3433,7 +3434,8 @@ slab_alloc(struct kmem_cache *cachep, gfp_t flags, unsigned long caller)
 	flags &= gfp_allowed_mask;
 
 	lockdep_trace_alloc(flags);
-	WARN_ON_ONCE((flags & __GFP_FS) && current->journal_info);
+	WARN_ON_ONCE((flags & __GFP_FS) && current->journal_info &&
+		!(current->flags & PF_MEMALLOC));
 
 	if (slab_should_failslab(cachep, flags))
 		return NULL;
diff --git a/mm/slub.c b/mm/slub.c
index 280adf6..96a7aba 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1266,7 +1266,8 @@ static inline int slab_pre_alloc_hook(struct kmem_cache *s, gfp_t flags)
 	flags &= gfp_allowed_mask;
 	lockdep_trace_alloc(flags);
 	might_sleep_if(flags & __GFP_WAIT);
-	WARN_ON_ONCE((flags & __GFP_FS) && current->journal_info);
+	WARN_ON_ONCE((flags & __GFP_FS) && current->journal_info &&
+		!(current->flags & PF_MEMALLOC));
 
 	return should_failslab(s->object_size, flags, s->flags);
 }
-- 
2.10.2