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quota: Check that quota is not dirty before release

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There is a race window where quota was redirted once we drop dq_list_lock inside dqput(),
but before we grab dquot->dq_lock inside dquot_release()

TASK1                                                       TASK2 (chowner)
->dqput()
  we_slept:
    spin_lock(&dq_list_lock)
    if (dquot_dirty(dquot)) {
          spin_unlock(&dq_list_lock);
          dquot->dq_sb->dq_op->write_dquot(dquot);
          goto we_slept
    if (test_bit(DQ_ACTIVE_B, &dquot->dq_flags)) {
          spin_unlock(&dq_list_lock);
          dquot->dq_sb->dq_op->release_dquot(dquot);
                                                            dqget()
							    mark_dquot_dirty()
							    dqput()
          goto we_slept;
        }
So dquot dirty quota will be released by TASK1, but on next we_sleept loop
we detect this and call ->write_dquot() for it.
XFSTEST: 440a80d4cb

Link: https://lore.kernel.org/r/20191031103920.3919-2-dmonakhov@openvz.org
CC: stable@vger.kernel.org
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
Signed-off-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Dmitry Monakhov
2019-10-31 10:39:20 +00:00
committed by Jan Kara
parent 6ff33d99fc
commit df4bb5d128
3 changed files with 12 additions and 2 deletions
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10
include/linux/quotaops.h
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@@ -54,6 +54,16 @@ static inline struct dquot *dqgrab(struct dquot *dquot)
atomic_inc(&dquot->dq_count);
return dquot;
}
static inline bool dquot_is_busy(struct dquot *dquot)
{
if (test_bit(DQ_MOD_B, &dquot->dq_flags))
return true;
if (atomic_read(&dquot->dq_count) > 1)
return true;
return false;
}
void dqput(struct dquot *dquot);
int dquot_scan_active(struct super_block *sb,
int (*fn)(struct dquot *dquot, unsigned long priv),