https://bugzilla.kernel.org/show_bug.cgi?id=55651 Summary: Non-atomic short write problem with O_APPEND Product: File System Version: 2.5 Kernel Version: 3.8.4 Platform: All OS/Version: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: ext4 AssignedTo: fs_ext4@xxxxxxxxxxxxxxxxxxxx ReportedBy: qbarnes@xxxxxxxxx Regression: No Created an attachment (id=96041) --> (https://bugzilla.kernel.org/attachment.cgi?id=96041) C program to demonstrate problem with non-atomic short writes. With recent kernels, short writes to a regular file opened with O_APPEND can be non-atomic when receiving a signal, and the write syscall is still returning bytes written == nbytes. I tried this with v3.8.4 (latest stable) and as far back as v3.2.41 and a smattering in between. All show this problem. However, it does not reproduce on v3.0.70 or earlier kernels. All testing was done with on x86_64 SMP systems and on an ext3 or ext4 file system. (I also tried running with only a single CPU enabled. It made no difference.) This is likely going to not be a problem specifically with the ext file system, but it seemed the best Bugzilla match that I saw based on the information gathered so far. The problem did not reproduce on an OpenSUSE 12.1 system (3.1.10-1.19-default). In the world of RHEL kernels, this problem does not appear with RHEL5.7 or earlier RHEL kernels I tried. However, it does appear starting with RHEL5.8 and 5.9 and also on RHEL6 kernels that I tried (6.2 & 6.4). I can't find anything wrong with the attached demo program, or find anything in the POSIX standard or with the Linux open(2) man pages that might allow for this apparent erroneous behavior. To reproduce the problem, compile and run the program below. After it's been running a say 4-6 seconds, press ^C. Notice there's been no output from the program (for every write call made, all returned success and with scnt==wcnt). Now run "grep '^P.*P' test.log". If there is no problem, there will be no output. If you see output, you'll see lines that were stepped on or otherwise not fully written out. -- Configure bugmail: https://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are watching the assignee of the bug. -- 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
