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Vlastimil Babka
62be1511b1
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 commita8161d1ed6("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:a8161d1ed6("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>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.