Commit f2c817be authored Jun 01, 2020 by Matthew Wilcox (Oracle) Committed by Linus Torvalds Jun 02, 2020

mm: use memalloc_nofs_save in readahead path



Ensure that memory allocations in the readahead path do not attempt to
reclaim file-backed pages, which could lead to a deadlock.  It is
possible, though unlikely this is the root cause of a problem observed
by Cong Wang.

Reported-by: Cong Wang <xiyou.wangcong@gmail.com>
Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-16-willy@infradead.org


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 2d8163e4

mm/readahead.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -22,6 +22,7 @@
		#include <linux/mm_inline.h>
		#include <linux/blk-cgroup.h>
		#include <linux/fadvise.h>
		#include <linux/sched/mm.h>

		#include "internal.h"

		@@ -185,6 +186,18 @@ void page_cache_readahead_unbounded(struct address_space *mapping,
		};
		unsigned long i;

		/*
		* Partway through the readahead operation, we will have added
		* locked pages to the page cache, but will not yet have submitted
		* them for I/O. Adding another page may need to allocate memory,
		* which can trigger memory reclaim. Telling the VM we're in
		* the middle of a filesystem operation will cause it to not
		* touch file-backed pages, preventing a deadlock. Most (all?)
		* filesystems already specify __GFP_NOFS in their mapping's
		* gfp_mask, but let's be explicit here.
		*/
		unsigned int nofs = memalloc_nofs_save();

		/*
		* Preallocate as many pages as we will need.
		*/
		@@ -229,6 +242,7 @@ void page_cache_readahead_unbounded(struct address_space *mapping,
		* will then handle the error.
		*/
		read_pages(&rac, &page_pool, false);
		memalloc_nofs_restore(nofs);
		}
		EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded);

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