| From 62be1511b1db8066220b18b7d4da2e6b9fdc69fb Mon Sep 17 00:00:00 2001 |
| From: Vlastimil Babka <vbabka@suse.cz> |
| Date: Mon, 8 May 2017 15:59:46 -0700 |
| Subject: [PATCH] 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> |
| Cc: <stable@vger.kernel.org> |
| Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
| Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
| |
| 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; |
| -- |
| 2.12.0 |
| |