On Fri, Feb 07, 2020 at 09:29:11AM -0500, Qian Cai wrote: > EXT4_I(inode)->i_disksize could be accessed concurrently as noticed by > KCSAN, > > BUG: KCSAN: data-race in ext4_write_end [ext4] / ext4_writepages [ext4] > > write to 0xffff91c6713b00f8 of 8 bytes by task 49268 on cpu 127: > ext4_write_end+0x4e3/0x750 [ext4] > ext4_update_i_disksize at fs/ext4/ext4.h:3032 > (inlined by) ext4_update_inode_size at fs/ext4/ext4.h:3046 > (inlined by) ext4_write_end at fs/ext4/inode.c:1287 > generic_perform_write+0x208/0x2a0 > ext4_buffered_write_iter+0x11f/0x210 [ext4] > ext4_file_write_iter+0xce/0x9e0 [ext4] > new_sync_write+0x29c/0x3b0 > __vfs_write+0x92/0xa0 > vfs_write+0x103/0x260 > ksys_write+0x9d/0x130 > __x64_sys_write+0x4c/0x60 > do_syscall_64+0x91/0xb47 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > read to 0xffff91c6713b00f8 of 8 bytes by task 24872 on cpu 37: > ext4_writepages+0x10ac/0x1d00 [ext4] > mpage_map_and_submit_extent at fs/ext4/inode.c:2468 > (inlined by) ext4_writepages at fs/ext4/inode.c:2772 > do_writepages+0x5e/0x130 > __writeback_single_inode+0xeb/0xb20 > writeback_sb_inodes+0x429/0x900 > __writeback_inodes_wb+0xc4/0x150 > wb_writeback+0x4bd/0x870 > wb_workfn+0x6b4/0x960 > process_one_work+0x54c/0xbe0 > worker_thread+0x80/0x650 > kthread+0x1e0/0x200 > ret_from_fork+0x27/0x50 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 37 PID: 24872 Comm: kworker/u261:2 Tainted: G W O L 5.5.0-next-20200204+ #5 > Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 > Workqueue: writeback wb_workfn (flush-7:0) > > Since only the read is operating as lockless (outside of the > "i_data_sem"), load tearing could introduce a logic bug. Fix it by > adding READ_ONCE() for the read and WRITE_ONCE() for the write. > > Signed-off-by: Qian Cai <cai@xxxxxx> Thanks, applied. - Ted
