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b=XUp703cPR/HSw0a8/8lfRjHaqFn9t0WI+Nv1Lqu4oCneg0qSBOCIaRVhWoBMvFihE hubkxs4n3OSP8nyltNh3CnWnX+6rChgqSOeRDOQL6OkR+6FFuwHaLWsjG/44cG6sm+ BVNP9XtIwPisO6tQX6KR/gO7X779mL6VQ8DS8niiCm0egq86yc/jZChwjP/+5MO3S/ /k9cpxNbznjwQJEtH/+wy0KKikGmGzDYLeYQMQNY/HKasecyoCxovE06wz2errblKo gDRBkBZlbdz3eTt8edpqxIoUUG6BiWy/pl/HalkbSdkd9nm7trgO65IOjeer9fq/IN F2mZwWFUw1OEw== Received: by cwcc.thunk.org (Postfix, from userid 15806) id E425915C02FC; Sat, 3 Feb 2024 12:56:25 -0500 (EST) Date: Sat, 3 Feb 2024 12:56:25 -0500 From: "Theodore Ts'o" To: Zhang Yi Cc: linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, adilger.kernel@dilger.ca, jack@suse.cz, ritesh.list@gmail.com, hch@infradead.org, djwong@kernel.org, willy@infradead.org, zokeefe@google.com, yi.zhang@huawei.com, chengzhihao1@huawei.com, yukuai3@huawei.com, wangkefeng.wang@huawei.com Subject: Re: [PATCH v3 02/26] ext4: convert to exclusive lock while inserting delalloc extents Message-ID: <20240203175625.GE36616@mit.edu> References: <20240127015825.1608160-1-yi.zhang@huaweicloud.com> <20240127015825.1608160-3-yi.zhang@huaweicloud.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240127015825.1608160-3-yi.zhang@huaweicloud.com> X-Rspamd-Queue-Id: B9A17120025 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: uagfef7qwuzbp1bnjxta151pcqbmak1g X-HE-Tag: 1706983033-504790 X-HE-Meta: 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 8O0bXztC HdnEkguE3aqCo/d+UoWJudSiBI4QgFt/dggQoM7YY7k4UdmCgOkpkVg3o+eZPrxxeheGJboDnzYYPTL57SSGzsp6+FWjqukU2u9xOVdlzVmQ284D1VkkgsFtEpjNpgBW9xwff3l5kIWf01r+Z+wWL0y1agMcmcCZWb0Dqn9bLyTxGkt7cMLDMKczvQpAO2pzshkCZacJ8ZvbIGxHHPE528mZOQz34xj0UATyCOrGn8sf7duSsjFE4d2tHUCUN/guW2C6po2UMlbSk3rVA9oqw43/Cf7tZxbXkTD/2AbYYw2ax73+ZxkV2Zu0p55y+e93K04/I X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jan 27, 2024 at 09:58:01AM +0800, Zhang Yi wrote: > From: Zhang Yi > > ext4_da_map_blocks() only hold i_data_sem in shared mode and i_rwsem > when inserting delalloc extents, it could be raced by another querying > path of ext4_map_blocks() without i_rwsem, .e.g buffered read path. > Suppose we buffered read a file containing just a hole, and without any > cached extents tree, then it is raced by another delayed buffered write > to the same area or the near area belongs to the same hole, and the new > delalloc extent could be overwritten to a hole extent. > > pread() pwrite() > filemap_read_folio() > ext4_mpage_readpages() > ext4_map_blocks() > down_read(i_data_sem) > ext4_ext_determine_hole() > //find hole > ext4_ext_put_gap_in_cache() > ext4_es_find_extent_range() > //no delalloc extent > ext4_da_map_blocks() > down_read(i_data_sem) > ext4_insert_delayed_block() > //insert delalloc extent > ext4_es_insert_extent() > //overwrite delalloc extent to hole > > This race could lead to inconsistent delalloc extents tree and > incorrect reserved space counter. Fix this by converting to hold > i_data_sem in exclusive mode when adding a new delalloc extent in > ext4_da_map_blocks(). > > Cc: stable@vger.kernel.org > Signed-off-by: Zhang Yi > Suggested-by: Jan Kara > Reviewed-by: Jan Kara Thanks, applied. - Ted