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authorAmir Goldstein <amir73il@gmail.com>2017-09-17 14:07:09 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-09-20 08:20:02 +0200
commitf46a61f686b0a8042ee4b7cb108ece81e3fb9401 (patch)
tree3a19252b7ed04cecac738ce857ea0ed90a2c0265
parent0e8d7e364ec546c44762664d30f4b1f6fd912197 (diff)
downloadlinux-linaro-stable-f46a61f686b0a8042ee4b7cb108ece81e3fb9401.tar.gz
xfs: fix incorrect log_flushed on fsync
commit 47c7d0b19502583120c3f396c7559e7a77288a68 upstream. When calling into _xfs_log_force{,_lsn}() with a pointer to log_flushed variable, log_flushed will be set to 1 if: 1. xlog_sync() is called to flush the active log buffer AND/OR 2. xlog_wait() is called to wait on a syncing log buffers xfs_file_fsync() checks the value of log_flushed after _xfs_log_force_lsn() call to optimize away an explicit PREFLUSH request to the data block device after writing out all the file's pages to disk. This optimization is incorrect in the following sequence of events: Task A Task B ------------------------------------------------------- xfs_file_fsync() _xfs_log_force_lsn() xlog_sync() [submit PREFLUSH] xfs_file_fsync() file_write_and_wait_range() [submit WRITE X] [endio WRITE X] _xfs_log_force_lsn() xlog_wait() [endio PREFLUSH] The write X is not guarantied to be on persistent storage when PREFLUSH request in completed, because write A was submitted after the PREFLUSH request, but xfs_file_fsync() of task A will be notified of log_flushed=1 and will skip explicit flush. If the system crashes after fsync of task A, write X may not be present on disk after reboot. This bug was discovered and demonstrated using Josef Bacik's dm-log-writes target, which can be used to record block io operations and then replay a subset of these operations onto the target device. The test goes something like this: - Use fsx to execute ops of a file and record ops on log device - Every now and then fsync the file, store md5 of file and mark the location in the log - Then replay log onto device for each mark, mount fs and compare md5 of file to stored value Cc: Christoph Hellwig <hch@lst.de> Cc: Josef Bacik <jbacik@fb.com> Cc: <stable@vger.kernel.org> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--fs/xfs/xfs_log.c7
1 files changed, 0 insertions, 7 deletions
diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index fe5f3df8b253..33c9a3aae948 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -3337,8 +3337,6 @@ maybe_sleep:
*/
if (iclog->ic_state & XLOG_STATE_IOERROR)
return -EIO;
- if (log_flushed)
- *log_flushed = 1;
} else {
no_sleep:
@@ -3442,8 +3440,6 @@ try_again:
xlog_wait(&iclog->ic_prev->ic_write_wait,
&log->l_icloglock);
- if (log_flushed)
- *log_flushed = 1;
already_slept = 1;
goto try_again;
}
@@ -3477,9 +3473,6 @@ try_again:
*/
if (iclog->ic_state & XLOG_STATE_IOERROR)
return -EIO;
-
- if (log_flushed)
- *log_flushed = 1;
} else { /* just return */
spin_unlock(&log->l_icloglock);
}