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authorVlastimil Babka <[email protected]>2017-05-08 15:59:46 -0700
committerLinus Torvalds <[email protected]>2017-05-08 17:15:15 -0700
commit62be1511b1db8066220b18b7d4da2e6b9fdc69fb (patch)
treeca0c513abfda095e443c388e5e920d01c18c908a
parent3b6521f53572d7fc1b40c93931948716a53a82ab (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/[email protected] Signed-off-by: Vlastimil Babka <[email protected]> Reported-by: Andrey Ryabinin <[email protected]> Acked-by: Michal Hocko <[email protected]> Acked-by: Hillf Danton <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Boris Brezillon <[email protected]> Cc: Chris Leech <[email protected]> Cc: "David S. Miller" <[email protected]> Cc: Eric Dumazet <[email protected]> Cc: Josef Bacik <[email protected]> Cc: Lee Duncan <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Richard Weinberger <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
-rw-r--r--mm/page_alloc.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e7486afa7fa7..1daf509722c7 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;