From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> Subject: 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. Link: http://lkml.kernel.org/r/20200414150233.24495-16-willy@xxxxxxxxxxxxx Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reported-by: Cong Wang <xiyou.wangcong@xxxxxxxxx> Suggested-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: William Kucharski <william.kucharski@xxxxxxxxxx> Cc: Chao Yu <yuchao0@xxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Cc: Dave Chinner <dchinner@xxxxxxxxxx> Cc: Eric Biggers <ebiggers@xxxxxxxxxx> Cc: Gao Xiang <gaoxiang25@xxxxxxxxxx> Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Joseph Qi <joseph.qi@xxxxxxxxxxxxxxxxx> Cc: Junxiao Bi <junxiao.bi@xxxxxxxxxx> Cc: Zi Yan <ziy@xxxxxxxxxx> Cc: Johannes Thumshirn <johannes.thumshirn@xxxxxxx> Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/readahead.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) --- a/mm/readahead.c~mm-use-memalloc_nofs_save-in-readahead-path +++ a/mm/readahead.c @@ -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" @@ -186,6 +187,18 @@ void page_cache_readahead_unbounded(stru 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. */ for (i = 0; i < nr_to_read; i++) { @@ -229,6 +242,7 @@ void page_cache_readahead_unbounded(stru * will then handle the error. */ read_pages(&rac, &page_pool, false); + memalloc_nofs_restore(nofs); } EXPORT_SYMBOL_GPL(page_cache_readahead_unbounded); _
