gfs2: fix quota refresh race in do_glock()
quotad periodically syncs in-memory quotas to the ondisk quota file and sets the QDF_REFRESH flag so that a subsequent read of a synced quota is re-read from disk. gfs2_quota_lock() checks for this flag and sets a 'force' bit to force re-read from disk if requested. However, there is a race condition here. It is possible for gfs2_quota_lock() to find the QDF_REFRESH flag unset (i.e force=0) and quotad comes in immediately after and syncs the relevant quota and sets the QDF_REFRESH flag. gfs2_quota_lock() resumes with force=0 and uses the stale in-memory quota usage values that result in miscalculations. This patch fixes this race by moving the check for the QDF_REFRESH flag check further out into the gfs2_quota_lock() process, i.e, in do_glock(), under the protection of the quota glock. Signed-off-by: NAbhi Das <adas@redhat.com> Signed-off-by: NBob Peterson <rpeterso@redhat.com> Acked-by: NSteven Whitehouse <swhiteho@redhat.com>
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