Messages in this thread Patch in this message |  | | From | Bob Peterson <> | Subject | [PATCH 9/9] gfs2: fix quota refresh race in do_glock() | Date | Mon, 13 Apr 2015 10:10:23 -0500 |
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From: Abhi Das <adas@redhat.com>
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: Abhi Das <adas@redhat.com> Signed-off-by: Bob Peterson <rpeterso@redhat.com> Acked-by: Steven Whitehouse <swhiteho@redhat.com> --- fs/gfs2/quota.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c index 5561468..5c27e48 100644 --- a/fs/gfs2/quota.c +++ b/fs/gfs2/quota.c @@ -923,6 +923,9 @@ restart: if (error) return error; + if (test_and_clear_bit(QDF_REFRESH, &qd->qd_flags)) + force_refresh = FORCE; + qd->qd_qb = *(struct gfs2_quota_lvb *)qd->qd_gl->gl_lksb.sb_lvbptr; if (force_refresh || qd->qd_qb.qb_magic != cpu_to_be32(GFS2_MAGIC)) { @@ -974,11 +977,8 @@ int gfs2_quota_lock(struct gfs2_inode *ip, kuid_t uid, kgid_t gid) sizeof(struct gfs2_quota_data *), sort_qd, NULL); for (x = 0; x < ip->i_res->rs_qa_qd_num; x++) { - int force = NO_FORCE; qd = ip->i_res->rs_qa_qd[x]; - if (test_and_clear_bit(QDF_REFRESH, &qd->qd_flags)) - force = FORCE; - error = do_glock(qd, force, &ip->i_res->rs_qa_qd_ghs[x]); + error = do_glock(qd, NO_FORCE, &ip->i_res->rs_qa_qd_ghs[x]); if (error) break; } -- 1.9.3
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