xfs: quiesce the filesystem after recovery on readonly mount
Recently we've had a number of reports where log recovery on a v5 filesystem has reported corruptions that looked to be caused by recovery being re-run over the top of an already-recovered metadata. This has uncovered a bug in recovery (fixed elsewhere) but the vector that caused this was largely unknown. A kdump test started tripping over this problem - the system would be crashed, the kdump kernel and environment would boot and dump the kernel core image, and then the system would reboot. After reboot, the root filesystem was triggering log recovery and corruptions were being detected. The metadumps indicated the above log recovery issue. What is happening is that the kdump kernel and environment is mounting the root device read-only to find the binaries needed to do it's work. The result of this is that it is running log recovery. However, because there were unlinked files and EFIs to be processed by recovery, the completion of phase 1 of log recovery could not mark the log clean. And because it's a read-only mount, the unmount process does not write records to the log to mark it clean, either. Hence on the next mount of the filesystem, log recovery was run again across all the metadata that had already been recovered and this is what triggered corruption warnings. To avoid this problem, we need to ensure that a read-only mount always updates the log when it completes the second phase of recovery. We already handle this sort of issue with rw->ro remount transitions, so the solution is as simple as quiescing the filesystem at the appropriate time during the mount process. This results in the log being marked clean so the mount behaviour recorded in the logs on repeated RO mounts will change (i.e. log recovery will no longer be run on every mount until a RW mount is done). This is a user visible change in behaviour, but it is harmless. Signed-off-by: NDave Chinner <dchinner@redhat.com> Reviewed-by: NEric Sandeen <sandeen@redhat.com> Signed-off-by: NDave Chinner <david@fromorbit.com>
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