On Thu 31-10-19 10:39:20, Dmitry Monakhov wrote:
> From: Dmitry Monakhov <dmtrmonakhov@xxxxxxxxxxxxxx>
>
> 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: https://github.com/dmonakhov/xfstests/commit/440a80d4cbb39e9234df4d7240aee1d551c36107
Yeah, good catch. Both patches look good to me. I've added them to my tree.
Honza
>
> Signed-off-by: Dmitry Monakhov <dmtrmonakhov@xxxxxxxxxxxxxx>
> ---
> fs/ocfs2/quota_global.c | 2 +-
> fs/quota/dquot.c | 2 +-
> include/linux/quotaops.h | 10 ++++++++++
> 3 files changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ocfs2/quota_global.c b/fs/ocfs2/quota_global.c
> index 7a92219..eda8348 100644
> --- a/fs/ocfs2/quota_global.c
> +++ b/fs/ocfs2/quota_global.c
> @@ -728,7 +728,7 @@ static int ocfs2_release_dquot(struct dquot *dquot)
>
> mutex_lock(&dquot->dq_lock);
> /* Check whether we are not racing with some other dqget() */
> - if (atomic_read(&dquot->dq_count) > 1)
> + if (dquot_is_busy(dquot))
> goto out;
> /* Running from downconvert thread? Postpone quota processing to wq */
> if (current == osb->dc_task) {
> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> index b492b9e..72d24a5 100644
> --- a/fs/quota/dquot.c
> +++ b/fs/quota/dquot.c
> @@ -497,7 +497,7 @@ int dquot_release(struct dquot *dquot)
>
> mutex_lock(&dquot->dq_lock);
> /* Check whether we are not racing with some other dqget() */
> - if (atomic_read(&dquot->dq_count) > 1)
> + if (dquot_is_busy(dquot))
> goto out_dqlock;
> if (dqopt->ops[dquot->dq_id.type]->release_dqblk) {
> ret = dqopt->ops[dquot->dq_id.type]->release_dqblk(dquot);
> diff --git a/include/linux/quotaops.h b/include/linux/quotaops.h
> index 185d948..91e0b76 100644
> --- a/include/linux/quotaops.h
> +++ b/include/linux/quotaops.h
> @@ -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),
> --
> 2.7.4
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
