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Date: Thu, 18 May 2017 12:46:16 +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 4.11 066/114] mm: prevent potential recursive reclaim due to clearing PF_MEMALLOC 4.11-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 @@ -3245,6 +3245,7 @@ __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; @@ -3252,7 +3253,7 @@ __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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