linux-kernel - [PATCH 4.10 61/93] mm: prevent potential recursive reclaim due to clearing PF

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Message-Id: <20170518104745.586747995@linuxfoundation.org>
Date:   Thu, 18 May 2017 12:47:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Michal Hocko <mhocko@...e.com>,
        Hillf Danton <hillf.zj@...baba-inc.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Johannes Weiner <hannes@...xchg.org>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        Chris Leech <cleech@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Josef Bacik <jbacik@...com>, Lee Duncan <lduncan@...e.com>,
        Richard Weinberger <richard@....at>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.10 61/93] mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC

4.10-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vlastimil Babka <vbabka@...e.cz>

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@...e.cz>
Reported-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: Hillf Danton <hillf.zj@...baba-inc.com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Johannes Weiner <hannes@...xchg.org>
Cc: Boris Brezillon <boris.brezillon@...e-electrons.com>
Cc: Chris Leech <cleech@...hat.com>
Cc: "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>
Cc: Josef Bacik <jbacik@...com>
Cc: Lee Duncan <lduncan@...e.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Richard Weinberger <richard@....at>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 mm/page_alloc.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3144,6 +3144,7 @@ __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;
@@ -3151,7 +3152,7 @@ __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;