Commit 4e434d4fe28a40d437573f25c9326b230217f017
Committed by
Greg Kroah-Hartman
1 parent
945d0ecdd9
Exists in
smarct4x-processor-sdk-04.01.00.06
and in
1 other branch
mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC
commit 62be1511b1db8066220b18b7d4da2e6b9fdc69fb upstream. 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Showing 1 changed file with 2 additions and 1 deletions Side-by-side Diff
mm/page_alloc.c
... | ... | @@ -3125,6 +3125,7 @@ |
3125 | 3125 | enum compact_priority prio, enum compact_result *compact_result) |
3126 | 3126 | { |
3127 | 3127 | struct page *page; |
3128 | + unsigned int noreclaim_flag = current->flags & PF_MEMALLOC; | |
3128 | 3129 | |
3129 | 3130 | if (!order) |
3130 | 3131 | return NULL; |
... | ... | @@ -3132,7 +3133,7 @@ |
3132 | 3133 | current->flags |= PF_MEMALLOC; |
3133 | 3134 | *compact_result = try_to_compact_pages(gfp_mask, order, alloc_flags, ac, |
3134 | 3135 | prio); |
3135 | - current->flags &= ~PF_MEMALLOC; | |
3136 | + current->flags = (current->flags & ~PF_MEMALLOC) | noreclaim_flag; | |
3136 | 3137 | |
3137 | 3138 | if (*compact_result <= COMPACT_INACTIVE) |
3138 | 3139 | return NULL; |