inode::i_size could be accessed concurently as noticed by KCSAN, BUG: KCSAN: data-race in iomap_do_writepage / iomap_write_end write to 0xffff8bf68fc0cac0 of 8 bytes by task 7484 on cpu 71: iomap_write_end+0xea/0x530 i_size_write at include/linux/fs.h:888 (inlined by) iomap_write_end at fs/iomap/buffered-io.c:782 iomap_write_actor+0x132/0x200 iomap_apply+0x245/0x8a5 iomap_file_buffered_write+0xbd/0xf0 xfs_file_buffered_aio_write+0x1c2/0x790 [xfs] xfs_file_write_iter+0x232/0x2d0 [xfs] 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+0x91/0xb05 entry_SYSCALL_64_after_hwframe+0x49/0xbe read to 0xffff8bf68fc0cac0 of 8 bytes by task 5901 on cpu 70: iomap_do_writepage+0xf4/0x450 i_size_read at include/linux/fs.h:866 (inlined by) iomap_do_writepage at fs/iomap/buffered-io.c:1558 write_cache_pages+0x523/0xb20 iomap_writepages+0x47/0x80 xfs_vm_writepages+0xc7/0x100 [xfs] do_writepages+0x5e/0x130 __writeback_single_inode+0xd5/0xb20 writeback_sb_inodes+0x429/0x910 __writeback_inodes_wb+0xc4/0x150 wb_writeback+0x47b/0x830 wb_workfn+0x688/0x930 process_one_work+0x54f/0xb90 worker_thread+0x80/0x5f0 kthread+0x1cd/0x1f0 ret_from_fork+0x27/0x50 Reported by Kernel Concurrency Sanitizer on: CPU: 70 PID: 5901 Comm: kworker/u257:2 Tainted: G L 5.6.0-rc2-next-20200218+ #2 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 Workqueue: writeback wb_workfn (flush-254:0) The write is protected by exclusive inode::i_rwsem (in xfs_file_buffered_aio_write()) but the read is not. A shattered value could introduce a logic bug. Fixed it using a pair of WRITE/READ_ONCE(). Signed-off-by: Qian Cai <cai@xxxxxx> --- include/linux/fs.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/fs.h b/include/linux/fs.h index 3cd4fe6b845e..25f98da90cf3 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -863,7 +863,7 @@ static inline loff_t i_size_read(const struct inode *inode) preempt_enable(); return i_size; #else - return inode->i_size; + return READ_ONCE(inode->i_size); #endif } @@ -885,7 +885,7 @@ static inline void i_size_write(struct inode *inode, loff_t i_size) inode->i_size = i_size; preempt_enable(); #else - inode->i_size = i_size; + WRITE_ONCE(inode->i_size, i_size); #endif } -- 2.21.0 (Apple Git-122.2)
