https://bugzilla.kernel.org/show_bug.cgi?id=205571 Bug ID: 205571 Summary: potential data race on ext4_setattr around inode->i_mtime with ftruncate and readv Product: File System Version: 2.5 Kernel Version: 5.4-rc5 Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: ext4 Assignee: fs_ext4@xxxxxxxxxxxxxxxxxxxx Reporter: mengxu.gatech@xxxxxxxxx Regression: No I am bringing up the visibility of a potential data race on ext4_setattr around inode->i_mtime when one thread is doing ftruncate and the other readv. [Setup] creat(file_bar, 0777, ) = 4; dup2(4, 198) = 198; link(file_bar, link_bar) = 0; open(link_bar, 0x2, 0777) = 6; dup2(6, 196) = 196; [Thread 1] ftruncate(198, 21009); [Thread 2] readv(196, [{iov_base=0x0x7fa652a1fa07, iov_len=1641}, ,..], 6); The function call trace is shown below: [Thread 1: SYS_ftruncate] __do_sys_ftruncate do_sys_ftruncate do_truncate ext4_setattr [WRITE] inode->i_mtime = current_time(inode); [Thread 2: SYS_readv] __do_sys_readv do_readv vfs_readv do_iter_read do_iter_readv_writev call_read_iter ext4_file_read_iter generic_file_read_iter generic_file_buffered_read file_accessed atime_needs_update relatime_need_update [READ] if (timespec64_compare(&inode->i_mtime, &inode->i_atime) >= 0) I could confirm that the WRITE may happen before and after the READ operation by controlling the timing of the two threads, i.e., by setting breakpoints before the WRITE statement. However, I am not very sure about the implication of such a data race (e.g., causing violations of assumptions). I would appreciate if you could help check on this potential bug and advise whether this is a harmful data race or it is intended. Thank you! -- You are receiving this mail because: You are watching the assignee of the bug.
