[PATCH 1/2] fs/quota: fix livelock in dquot_writeback_dquots

[PATCH 1/2] fs/quota: fix livelock in dquot_writeback_dquots

[Dmitry Monakhov]

From: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>

Write only quotas which are dirty at entry.


XFSTEST: https://github.com/dmonakhov/xfstests/commit/b10ad23566a5bf75832a6f500e1236084083cddc

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
---
 fs/quota/dquot.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 26812a6..b492b9e 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -622,7 +622,7 @@ EXPORT_SYMBOL(dquot_scan_active);
 /* Write all dquot structures to quota files */
 int dquot_writeback_dquots(struct super_block *sb, int type)
 {
-	struct list_head *dirty;
+	struct list_head dirty;
 	struct dquot *dquot;
 	struct quota_info *dqopt = sb_dqopt(sb);
 	int cnt;
@@ -636,9 +636,10 @@ int dquot_writeback_dquots(struct super_block *sb, int type)
 		if (!sb_has_quota_active(sb, cnt))
 			continue;
 		spin_lock(&dq_list_lock);
-		dirty = &dqopt->info[cnt].dqi_dirty_list;
-		while (!list_empty(dirty)) {
-			dquot = list_first_entry(dirty, struct dquot,
+		/* Move list away to avoid livelock. */
+		list_replace_init(&dqopt->info[cnt].dqi_dirty_list, &dirty);
+		while (!list_empty(&dirty)) {
+			dquot = list_first_entry(&dirty, struct dquot,
 						 dq_dirty);
 
 			WARN_ON(!test_bit(DQ_ACTIVE_B, &dquot->dq_flags));
-- 
2.7.4

[PATCH 2/2] fs/quota: Check that quota is not dirty before release

[Dmitry Monakhov]

From: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>

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

Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
---
 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

Re: [PATCH 2/2] fs/quota: Check that quota is not dirty before release

[Jan Kara]

On Thu 31-10-19 10:39:20, Dmitry Monakhov wrote:
> From: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
> 
> 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@yandex-team.ru>
> ---
>  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@suse.com>
SUSE Labs, CR

Re: [PATCH 2/2] fs/quota: Check that quota is not dirty before release

[Jan Kara]

On Thu 31-10-19 19:00:33, Jan Kara wrote:
> On Thu 31-10-19 10:39:20, Dmitry Monakhov wrote:
> > From: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
> > 
> > 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.

And forgot to add: Thanks for both patches and also the regression tests! I
really appreciate it!

								Honza


> > Signed-off-by: Dmitry Monakhov <dmtrmonakhov@yandex-team.ru>
> > ---
> >  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@suse.com>
> SUSE Labs, CR
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR