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mm/page_alloc.c: avoid potential NULL pointer dereference

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ac.preferred_zoneref->zone passed to alloc_flags_nofragment() can be NULL.
'zone' pointer unconditionally derefernced in alloc_flags_nofragment().
Bail out on NULL zone to avoid potential crash.  Currently we don't see
any crashes only because alloc_flags_nofragment() has another bug which
allows compiler to optimize away all accesses to 'zone'.

Change-Id: I93fbd4a42ae334c53f4845b8a496cfdb498f72ed
Link: http://lkml.kernel.org/r/20190423120806.3503-1-aryabinin@virtuozzo.com
Fixes: 6bb154504f8b ("mm, page_alloc: spread allocations across zones before introducing fragmentation")
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Git-commit: 8139ad043d632c0e9e12d760068a7a8e91659aa1
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
This commit is contained in:
Andrey Ryabinin 2019-04-25 22:23:58 -07:00 committed by Gerrit - the friendly Code Review server
parent 12d8e84753
commit dd0013f2c1
1 changed files with 3 additions and 0 deletions
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3
mm/page_alloc.c
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@ -3496,6 +3496,9 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
alloc_flags |= ALLOC_KSWAPD;
#ifdef CONFIG_ZONE_DMA32
if (!zone)
return alloc_flags;
if (zone_idx(zone) != ZONE_NORMAL)
goto out;