On Mon 31-08-15 21:33:46, Andrey Konovalov wrote: > Hi! > > We are working on a dynamic data race detector for the Linux kernel, > KernelThreadSanitizer (ktsan): > https://github.com/google/ktsan/wiki > > We got a report while running ktsan on 4.2: > > ================================================================== > ThreadSanitizer: data-race in __inode_add_bytes > > Write of size 8 by thread T210 (K740): > [<ffffffff81266435>] __inode_add_bytes+0x55/0xd0 fs/stat.c:451 > [<ffffffff812f90c0>] inode_claim_rsv_space+0x60/0xa0 fs/quota/dquot.c:1557 > [<ffffffff812f9f7b>] dquot_claim_space_nodirty+0x3b/0x280 fs/quota/dquot.c:1721 > [< inlined >] ext4_da_update_reserve_space+0x13b/0x2c0 > dquot_claim_block include/linux/quotaops.h:345 > [<ffffffff81335dab>] ext4_da_update_reserve_space+0x13b/0x2c0 > fs/ext4/inode.c:350 > [<ffffffff81384cf0>] ext4_ext_map_blocks+0x1570/0x1a30 fs/ext4/extents.c:4597 > [<ffffffff8133610a>] ext4_map_blocks+0x1da/0x7b0 fs/ext4/inode.c:592 > [< inlined >] ext4_writepages+0x976/0x1480 > mpage_map_one_extent fs/ext4/inode.c:2109 > [< inlined >] ext4_writepages+0x976/0x1480 > mpage_map_and_submit_extent fs/ext4/inode.c:2165 > [<ffffffff8133b7b6>] ext4_writepages+0x976/0x1480 fs/ext4/inode.c:2508 > [<ffffffff811dbd23>] do_writepages+0x53/0x80 mm/page-writeback.c:2332 > [<ffffffff812a76bf>] __writeback_single_inode+0x7f/0x530 > fs/fs-writeback.c:1259 (discriminator 3) > [<ffffffff812a7fd4>] writeback_sb_inodes+0x464/0x690 fs/fs-writeback.c:1516 > [<ffffffff812a82c1>] __writeback_inodes_wb+0xc1/0x100 fs/fs-writeback.c:1562 > [<ffffffff812a86ae>] wb_writeback+0x3ae/0x450 fs/fs-writeback.c:1666 > [< inlined >] wb_workfn+0x203/0x780 wb_do_writeback > fs/fs-writeback.c:1801 > [<ffffffff812a91c3>] wb_workfn+0x203/0x780 fs/fs-writeback.c:1852 > [<ffffffff810b06ce>] process_one_work+0x28e/0x710 kernel/workqueue.c:2036 > [<ffffffff810b1299>] worker_thread+0xb9/0x750 kernel/workqueue.c:2170 > [<ffffffff810b9c61>] kthread+0x161/0x180 kernel/kthread.c:209 > [<ffffffff81eb0a1f>] ret_from_fork+0x3f/0x70 arch/x86/entry/entry_64.S:526 > > Previous read of size 8 by thread T512 (K7200): > [< inlined >] ext4_mark_iloc_dirty+0x454/0xe20 > ext4_inode_blocks_set fs/ext4/inode.c:4272 > [< inlined >] ext4_mark_iloc_dirty+0x454/0xe20 > ext4_do_update_inode fs/ext4/inode.c:4430 > [<ffffffff8133a014>] ext4_mark_iloc_dirty+0x454/0xe20 fs/ext4/inode.c:4937 > [<ffffffff8133ab8b>] ext4_mark_inode_dirty+0xdb/0x390 fs/ext4/inode.c:5053 > [<ffffffff8133f929>] ext4_dirty_inode+0x59/0x80 fs/ext4/inode.c:5085 > [<ffffffff812a7319>] __mark_inode_dirty+0x2c9/0x5f0 fs/fs-writeback.c:2015 > [<ffffffff8128a58e>] generic_update_time+0xbe/0x150 fs/inode.c:1566 > [< inlined >] file_update_time+0x112/0x1b0 update_time fs/inode.c:1582 > [<ffffffff812890f2>] file_update_time+0x112/0x1b0 fs/inode.c:1785 > [<ffffffff811cb175>] __generic_file_write_iter+0x105/0x2e0 mm/filemap.c:2570 > [<ffffffff8132c3a4>] ext4_file_write_iter+0x254/0x740 fs/ext4/file.c:170 > [< inlined >] __vfs_write+0x19c/0x1e0 new_sync_write fs/read_write.c:478 > [<ffffffff8125d48c>] __vfs_write+0x19c/0x1e0 fs/read_write.c:491 > [<ffffffff8125dde6>] vfs_write+0xf6/0x2a0 fs/read_write.c:538 > [< inlined >] SyS_write+0x6b/0xd0 SYSC_write fs/read_write.c:585 > [<ffffffff8125f37b>] SyS_write+0x6b/0xd0 fs/read_write.c:577 > [<ffffffff81eb062e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > ================================================================== > > The 'inode->i_blocks' field is updated in one thread, while being read > and used in another. > > This can probably be fixed with a few READ_ONCE/WRITE_ONCE or by > taking inode->i_lock in ext4_inode_blocks_set. Yeah, the right fix would be to use inode->i_lock as quota code does, possibly with a wrapper function so that it can be avoided for 64-bit archs (see how i_size_read() / i_size_write() gets handled). However if you're going to fix this (and I'd note that this race is mostly theoretical since it would require 32-bit architecture and a file using more than 2TB of space) it's not just about ext4_inode_blocks_set() but about auditing all the other places working with i_blocks which is kind of a pain given the theoretical nature of the race... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
