From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 028/128] mm: use memalloc_nofs_save in readahead path Date: Tue, 02 Jun 2020 13:11:35 -0700 Message-ID: <20200602201135.RE2ZMIqnG%akpm@linux-foundation.org> References: <20200602130930.8e8f10fa6f19e3766e70921f@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Return-path: Received: from mail.kernel.org ([198.145.29.99]:54810 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726112AbgFBULh (ORCPT ); Tue, 2 Jun 2020 16:11:37 -0400 In-Reply-To: <20200602130930.8e8f10fa6f19e3766e70921f@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, darrick.wong@oracle.com, dchinner@redhat.com, ebiggers@google.com, gaoxiang25@huawei.com, hch@lst.de, jaegeuk@kernel.org, jhubbard@nvidia.com, johannes.thumshirn@wdc.com, joseph.qi@linux.alibaba.com, junxiao.bi@oracle.com, linux-mm@kvack.org, mhocko@suse.com, mm-commits@vger.kernel.org, mszeredi@redhat.com, torvalds@linux-foundation.org, william.kucharski@oracle.com, willy@infradead.org, xiyou.wangcong@gmail.com, yuchao0@huawei.com, ziy@nvidia.com From: "Matthew Wilcox (Oracle)" 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@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Reported-by: Cong Wang Suggested-by: Michal Hocko Reviewed-by: William Kucharski Cc: Chao Yu Cc: Christoph Hellwig Cc: Darrick J. Wong Cc: Dave Chinner Cc: Eric Biggers Cc: Gao Xiang Cc: Jaegeuk Kim Cc: John Hubbard Cc: Joseph Qi Cc: Junxiao Bi Cc: Zi Yan Cc: Johannes Thumshirn Cc: Miklos Szeredi Signed-off-by: Andrew Morton --- 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 #include #include +#include #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); _