From: Vlastimil Babka <vbabka@xxxxxxx>
Subject: 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@xxxxxxx
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Reported-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx>
Cc: Chris Leech <cleech@xxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Josef Bacik <jbacik@xxxxxx>
Cc: Lee Duncan <lduncan@xxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Richard Weinberger <richard@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff -puN mm/page_alloc.c~mm-prevent-potential-recursive-reclaim-due-to-clearing-pf_memalloc mm/page_alloc.c
--- a/mm/page_alloc.c~mm-prevent-potential-recursive-reclaim-due-to-clearing-pf_memalloc
+++ a/mm/page_alloc.c
@@ -3283,6 +3283,7 @@ __alloc_pages_direct_compact(gfp_t gfp_m
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_m
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;
_
--
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