diff options
author | Vlastimil Babka <vbabka@suse.cz> | 2017-04-27 09:58:05 +1000 |
---|---|---|
committer | Stephen Rothwell <sfr@canb.auug.org.au> | 2017-04-28 16:43:53 +1000 |
commit | fd549afddb9dec3da0233d529944d0d21c5eb2d4 (patch) | |
tree | eaeb65d83ee3b121774892594105cfccdcf23b1f | |
parent | 4a36ca655bb2b4e47e32d0b826a0f6cab1e41c97 (diff) |
mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC
Patch series "more robust PF_MEMALLOC handling"
This series aims to unify the setting and clearing of PF_MEMALLOC, which
prevents recursive reclaim. There are some places that clear the flag
unconditionally from current->flags, which may result in clearing a
pre-existing flag. This already resulted in a bug report that Patch 1
fixes (without the new helpers, to make backporting easier). Patch 2
introduces the new helpers, modelled after existing memalloc_noio_* and
memalloc_nofs_* helpers, and converts mm core to use them. Patches 3 and
4 convert non-mm code.
This patch (of 4):
__alloc_pages_direct_compact() sets PF_MEMALLOC to prevent deadlock during
page migration by lock_page() (see the comment in __unmap_and_move()).
Then it unconditionally clears the flag, which can clear a pre-existing
PF_MEMALLOC flag and result in recursive reclaim. This was not a problem
until commit a8161d1ed609 ("mm, page_alloc: restructure direct compaction
handling in slowpath"), because direct compation was called only after
direct reclaim, which was skipped when PF_MEMALLOC flag was set.
Even now it's only a theoretical issue, as the new callsite of
__alloc_pages_direct_compact() is reached only for costly orders and when
gfp_pfmemalloc_allowed() is true, which means either __GFP_NOMEMALLOC is
in gfp_flags or in_interrupt() is true. There is no such known context,
but let's play it safe and make __alloc_pages_direct_compact() robust for
cases where PF_MEMALLOC is already set.
Fixes: a8161d1ed609 ("mm, page_alloc: restructure direct compaction handling in slowpath")
Link: http://lkml.kernel.org/r/20170405074700.29871-2-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Reported-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Chris Leech <cleech@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Lee Duncan <lduncan@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r-- | mm/page_alloc.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9ed2b45b15d0..53bf2a90d570 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3283,6 +3283,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, enum compact_priority prio, enum compact_result *compact_result) { struct page *page; + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; if (!order) return NULL; @@ -3290,7 +3291,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order, current->flags |= PF_MEMALLOC; *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, prio); - current->flags &= ~PF_MEMALLOC; + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; if (*compact_result <= COMPACT_INACTIVE) return NULL; |