ocfs2: fix a potential 'ABBA' deadlock caused by 'l_lock' and 'dentry_attach_lock'

CPUA CPUB

ocfs2_dentry_convert_worker
get 'l_lock'

get 'dentry_attach_lock'

interruptted by dio_end_io:
dio_end_io
dio_bio_end_aio
dio_complete
dio->end_io
ocfs2_dio_end_io
ocfs2_rw_unlock
...
try to get 'l_lock'

but CPUA has got it.

try to get 'dentry_attach_lock',
but CPUB has got 'dentry_attach_lock', and would not release it.

so we need use spin_lock_irqsave for 'dentry_attach_lock' to prevent interruptted by softirq.

Signed-off-by Jun Piao <[email protected]>

Reviewed-by Alex Chen <[email protected]>

---
  fs/ocfs2/dcache.c  | 14 ++++++++------
  fs/ocfs2/dlmglue.c | 14 +++++++-------
  fs/ocfs2/namei.c   |  5 +++--
  3 files changed, 18 insertions(+), 15 deletions(-)

fs/ocfs2/dcache.c +8 -6

index 2903730..6555fbf 100644
@@ -230,6 +230,7 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
  	int ret;
  	struct dentry *alias;
  	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
  	trace_ocfs2_dentry_attach_lock(dentry->d_name.len, dentry->d_name.name,
  				       (unsigned long long)parent_blkno, dl);

@@ -309,10 +310,10 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
  	ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);
 
  out_attach:
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
  	dentry->d_fsdata = dl;
  	dl->dl_count++;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
  	/*
  	 * This actually gets us our PRMODE level lock. From now on,

@@ -333,9 +334,9 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
  	if (ret < 0 && !alias) {
  		ocfs2_lock_res_free(&dl->dl_lockres);
  		BUG_ON(dl->dl_count != 1);
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, flags);
  		dentry->d_fsdata = NULL;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, flags);
  		kfree(dl);
  		iput(inode);
  	}

@@ -379,13 +380,14 @@ void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
  			   struct ocfs2_dentry_lock *dl)
  {
  	int unlock = 0;
+	unsigned long flags;
 
  	BUG_ON(dl->dl_count == 0);
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
  	dl->dl_count--;
  	unlock = !dl->dl_count;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
  	if (unlock)
  		ocfs2_drop_dentry_lock(osb, dl);

fs/ocfs2/dlmglue.c +7 -7

index 4689940..9bff3d2 100644
@@ -3801,7 +3801,7 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  	struct ocfs2_dentry_lock *dl = ocfs2_lock_res_dl(lockres);
  	struct ocfs2_inode_info *oi = OCFS2_I(dl->dl_inode);
  	struct dentry *dentry;
-	unsigned long flags;
+	unsigned long flags, d_flags;
  	int extra_ref = 0;
 
  	/*

@@ -3831,13 +3831,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  	 * flag.
  	 */
  	spin_lock_irqsave(&lockres->l_lock, flags);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
  	if (!(lockres->l_flags & OCFS2_LOCK_FREEING)
  	    && dl->dl_count) {
  		dl->dl_count++;
  		extra_ref = 1;
  	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
  	spin_unlock_irqrestore(&lockres->l_lock, flags);
 
  	mlog(0, "extra_ref = %d\n", extra_ref);

@@ -3850,13 +3850,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  	if (!extra_ref)
  		return UNBLOCK_CONTINUE;
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
  	while (1) {
  		dentry = ocfs2_find_local_alias(dl->dl_inode,
  						dl->dl_parent_blkno, 1);
  		if (!dentry)
  			break;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
  		if (S_ISDIR(dl->dl_inode->i_mode))
  			shrink_dcache_parent(dentry);

@@ -3874,9 +3874,9 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  		d_delete(dentry);
  		dput(dentry);
 
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, d_flags);
  	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
  	/*
  	 * If we are the last holder of this dentry lock, there is no

fs/ocfs2/namei.c +3 -2

index 3b0a10d..a17454e 100644
@@ -223,13 +223,14 @@ static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb,
  		struct dentry *dentry, struct inode *inode)
  {
  	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
  	ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);
  	ocfs2_lock_res_free(&dl->dl_lockres);
  	BUG_ON(dl->dl_count != 1);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
  	dentry->d_fsdata = NULL;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
  	kfree(dl);
  	iput(inode);
  }

Hi Jun,

Quoted 4 lines · piaojun

CPUA CPUB

ocfs2_dentry_convert_worker
get 'l_lock'

This lock belongs to ocfs2_dentry_lock::ocfs2_lock_res::l_lock

Quoted 12 lines

get 'dentry_attach_lock'

interruptted by dio_end_io:
dio_end_io
dio_bio_end_aio
dio_complete
dio->end_io
ocfs2_dio_end_io
ocfs2_rw_unlock
...
try to get 'l_lock'

This lock belongs to ocfs2_lock_res::l_lock though.

So I think they are totally two different locks. So making spin_lock to interruption safe is pointless.

Thanks,
Changwei

Quoted 140 lines

but CPUA has got it.

try to get 'dentry_attach_lock',
but CPUB has got 'dentry_attach_lock', and would not release it.

so we need use spin_lock_irqsave for 'dentry_attach_lock' to prevent interruptted by softirq.

Signed-off-by Jun Piao <[email protected]>

Reviewed-by Alex Chen <[email protected]>

---
  fs/ocfs2/dcache.c  | 14 ++++++++------
  fs/ocfs2/dlmglue.c | 14 +++++++-------
  fs/ocfs2/namei.c   |  5 +++--
  3 files changed, 18 insertions(+), 15 deletions(-)

fs/ocfs2/dcache.c +8 -6

index 2903730..6555fbf 100644
@@ -230,6 +230,7 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
  	int ret;
  	struct dentry *alias;
  	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
  	trace_ocfs2_dentry_attach_lock(dentry->d_name.len, dentry->d_name.name,
  				       (unsigned long long)parent_blkno, dl);

@@ -309,10 +310,10 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
  	ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);
 
  out_attach:
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
  	dentry->d_fsdata = dl;
  	dl->dl_count++;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
  	/*
  	 * This actually gets us our PRMODE level lock. From now on,

@@ -333,9 +334,9 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
  	if (ret < 0 && !alias) {
  		ocfs2_lock_res_free(&dl->dl_lockres);
  		BUG_ON(dl->dl_count != 1);
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, flags);
  		dentry->d_fsdata = NULL;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, flags);
  		kfree(dl);
  		iput(inode);
  	}

@@ -379,13 +380,14 @@ void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
  			   struct ocfs2_dentry_lock *dl)
  {
  	int unlock = 0;
+	unsigned long flags;
 
  	BUG_ON(dl->dl_count == 0);
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
  	dl->dl_count--;
  	unlock = !dl->dl_count;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
  	if (unlock)
  		ocfs2_drop_dentry_lock(osb, dl);

fs/ocfs2/dlmglue.c +7 -7

index 4689940..9bff3d2 100644
@@ -3801,7 +3801,7 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  	struct ocfs2_dentry_lock *dl = ocfs2_lock_res_dl(lockres);
  	struct ocfs2_inode_info *oi = OCFS2_I(dl->dl_inode);
  	struct dentry *dentry;
-	unsigned long flags;
+	unsigned long flags, d_flags;
  	int extra_ref = 0;
 
  	/*

@@ -3831,13 +3831,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  	 * flag.
  	 */
  	spin_lock_irqsave(&lockres->l_lock, flags);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
  	if (!(lockres->l_flags & OCFS2_LOCK_FREEING)
  	    && dl->dl_count) {
  		dl->dl_count++;
  		extra_ref = 1;
  	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
  	spin_unlock_irqrestore(&lockres->l_lock, flags);
 
  	mlog(0, "extra_ref = %d\n", extra_ref);

@@ -3850,13 +3850,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  	if (!extra_ref)
  		return UNBLOCK_CONTINUE;
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
  	while (1) {
  		dentry = ocfs2_find_local_alias(dl->dl_inode,
  						dl->dl_parent_blkno, 1);
  		if (!dentry)
  			break;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
  		if (S_ISDIR(dl->dl_inode->i_mode))
  			shrink_dcache_parent(dentry);

@@ -3874,9 +3874,9 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
  		d_delete(dentry);
  		dput(dentry);
 
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, d_flags);
  	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
  	/*
  	 * If we are the last holder of this dentry lock, there is no

fs/ocfs2/namei.c +1 -0

index 3b0a10d..a17454e 100644
@@ -223,13 +223,14 @@ static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb,
  		struct dentry *dentry, struct inode *inode)
  {
  	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
  	ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);

fs/ocfs2/namei.c static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb, · line 236

Quoted 10 lines

fs/ocfs2/namei.c +2 -2

  	ocfs2_lock_res_free(&dl->dl_lockres);
  	BUG_ON(dl->dl_count != 1);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
  	dentry->d_fsdata = NULL;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
  	kfree(dl);
  	iput(inode);
  }

.

Hi Changwei,

Quoted 23 lines · Changwei Ge

Hi Jun,

Quoted 4 lines · piaojun

CPUA CPUB

ocfs2_dentry_convert_worker
get 'l_lock'

This lock belongs to ocfs2_dentry_lock::ocfs2_lock_res::l_lock

Quoted 12 lines

get 'dentry_attach_lock'

interruptted by dio_end_io:
dio_end_io
dio_bio_end_aio
dio_complete
dio->end_io
ocfs2_dio_end_io
ocfs2_rw_unlock
...
try to get 'l_lock'

Quoted 8 lines

This lock belongs to ocfs2_lock_res::l_lock though.

So I think they are totally two different locks. So making spin_lock to interruption safe is pointless.

Thanks,
Changwei

For the same lock, we need use spin_lock_irqsave to ensure irq-safe as you said. But the scenario described above is another kind of deadlock caused by two different locks which stuck each other. To avoid this 'ABBA' deadlock we need follow the rule that 'spin_lock_irqsave' should be called under 'spin_lock_irqsave'.

thanks,
Jun

Quoted 153 lines

Quoted 140 lines

but CPUA has got it.

try to get 'dentry_attach_lock',
but CPUB has got 'dentry_attach_lock', and would not release it.

so we need use spin_lock_irqsave for 'dentry_attach_lock' to prevent interruptted by softirq.

Signed-off-by Jun Piao <[email protected]>

Reviewed-by Alex Chen <[email protected]>

---
   fs/ocfs2/dcache.c  | 14 ++++++++------
   fs/ocfs2/dlmglue.c | 14 +++++++-------
   fs/ocfs2/namei.c   |  5 +++--
   3 files changed, 18 insertions(+), 15 deletions(-)

fs/ocfs2/dcache.c +8 -6

index 2903730..6555fbf 100644
@@ -230,6 +230,7 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
   	int ret;
   	struct dentry *alias;
   	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
   	trace_ocfs2_dentry_attach_lock(dentry->d_name.len, dentry->d_name.name,
   				       (unsigned long long)parent_blkno, dl);

@@ -309,10 +310,10 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
   	ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);
 
   out_attach:
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
   	dentry->d_fsdata = dl;
   	dl->dl_count++;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
   	/*
   	 * This actually gets us our PRMODE level lock. From now on,

@@ -333,9 +334,9 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
   	if (ret < 0 && !alias) {
   		ocfs2_lock_res_free(&dl->dl_lockres);
   		BUG_ON(dl->dl_count != 1);
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, flags);
   		dentry->d_fsdata = NULL;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, flags);
   		kfree(dl);
   		iput(inode);
   	}

@@ -379,13 +380,14 @@ void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
   			   struct ocfs2_dentry_lock *dl)
   {
   	int unlock = 0;
+	unsigned long flags;
 
   	BUG_ON(dl->dl_count == 0);
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
   	dl->dl_count--;
   	unlock = !dl->dl_count;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
   	if (unlock)
   		ocfs2_drop_dentry_lock(osb, dl);

fs/ocfs2/dlmglue.c +7 -7

index 4689940..9bff3d2 100644
@@ -3801,7 +3801,7 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   	struct ocfs2_dentry_lock *dl = ocfs2_lock_res_dl(lockres);
   	struct ocfs2_inode_info *oi = OCFS2_I(dl->dl_inode);
   	struct dentry *dentry;
-	unsigned long flags;
+	unsigned long flags, d_flags;
   	int extra_ref = 0;
 
   	/*

@@ -3831,13 +3831,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   	 * flag.
   	 */
   	spin_lock_irqsave(&lockres->l_lock, flags);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
   	if (!(lockres->l_flags & OCFS2_LOCK_FREEING)
   	    && dl->dl_count) {
   		dl->dl_count++;
   		extra_ref = 1;
   	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
   	spin_unlock_irqrestore(&lockres->l_lock, flags);
 
   	mlog(0, "extra_ref = %d\n", extra_ref);

@@ -3850,13 +3850,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   	if (!extra_ref)
   		return UNBLOCK_CONTINUE;
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
   	while (1) {
   		dentry = ocfs2_find_local_alias(dl->dl_inode,
   						dl->dl_parent_blkno, 1);
   		if (!dentry)
   			break;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
   		if (S_ISDIR(dl->dl_inode->i_mode))
   			shrink_dcache_parent(dentry);

@@ -3874,9 +3874,9 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   		d_delete(dentry);
   		dput(dentry);
 
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, d_flags);
   	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
   	/*
   	 * If we are the last holder of this dentry lock, there is no

fs/ocfs2/namei.c +1 -0

index 3b0a10d..a17454e 100644
@@ -223,13 +223,14 @@ static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb,
   		struct dentry *dentry, struct inode *inode)
   {
   	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
   	ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);

fs/ocfs2/namei.c static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb, · line 236

Quoted 10 lines

fs/ocfs2/namei.c +2 -2

   	ocfs2_lock_res_free(&dl->dl_lockres);
   	BUG_ON(dl->dl_count != 1);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
   	dentry->d_fsdata = NULL;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
   	kfree(dl);
   	iput(inode);
   }

.

Quoted 35 lines · piaojun

Hi Changwei,

Quoted 23 lines · Changwei Ge

Hi Jun,

Quoted 4 lines · piaojun

CPUA CPUB

ocfs2_dentry_convert_worker
get 'l_lock'

This lock belongs to ocfs2_dentry_lock::ocfs2_lock_res::l_lock

Quoted 12 lines

get 'dentry_attach_lock'

interruptted by dio_end_io:
dio_end_io
dio_bio_end_aio
dio_complete
dio->end_io
ocfs2_dio_end_io
ocfs2_rw_unlock
...
try to get 'l_lock'

Quoted 8 lines

This lock belongs to ocfs2_lock_res::l_lock though.

So I think they are totally two different locks. So making spin_lock to interruption safe is pointless.

Thanks,
Changwei

Quoted 5 lines

For the same lock, we need use spin_lock_irqsave to ensure irq-safe as you said. But the scenario described above is another kind of deadlock caused by two different locks which stuck each other. To avoid this 'ABBA' deadlock we need follow the rule that 'spin_lock_irqsave' should be called under 'spin_lock_irqsave'.

Hi Jun,
I'm not sure if you understood my concern?
I agree with that we should avoid ABBA dead lock scenario. But the dead lock scenario your sequence diagram is demonstrating doesn't even exist.

Because CPU A is holding lock _X1_ and waiting for _dentry_attach_lock_. meanwhile CPU B is holding lock _dentry_attach_lock_ and waiting for _X2_. No ABBA deadlock condition is met, CPU B will acquire lock _X2_ without being affected by CPU A.

In a nutshell, there are three locks(lock memory space) involved in your diagram rather than two.

Thanks,
Changwei

Quoted 158 lines

thanks,
Jun

Quoted 153 lines

Quoted 140 lines

but CPUA has got it.

try to get 'dentry_attach_lock',
but CPUB has got 'dentry_attach_lock', and would not release it.

so we need use spin_lock_irqsave for 'dentry_attach_lock' to prevent interruptted by softirq.

Signed-off-by Jun Piao <[email protected]>

Reviewed-by Alex Chen <[email protected]>

---
   fs/ocfs2/dcache.c  | 14 ++++++++------
   fs/ocfs2/dlmglue.c | 14 +++++++-------
   fs/ocfs2/namei.c   |  5 +++--
   3 files changed, 18 insertions(+), 15 deletions(-)

fs/ocfs2/dcache.c +8 -6

index 2903730..6555fbf 100644
@@ -230,6 +230,7 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
   	int ret;
   	struct dentry *alias;
   	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
   	trace_ocfs2_dentry_attach_lock(dentry->d_name.len, dentry->d_name.name,
   				       (unsigned long long)parent_blkno, dl);

@@ -309,10 +310,10 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
   	ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);
 
   out_attach:
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
   	dentry->d_fsdata = dl;
   	dl->dl_count++;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
   	/*
   	 * This actually gets us our PRMODE level lock. From now on,

@@ -333,9 +334,9 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
   	if (ret < 0 && !alias) {
   		ocfs2_lock_res_free(&dl->dl_lockres);
   		BUG_ON(dl->dl_count != 1);
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, flags);
   		dentry->d_fsdata = NULL;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, flags);
   		kfree(dl);
   		iput(inode);
   	}

@@ -379,13 +380,14 @@ void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
   			   struct ocfs2_dentry_lock *dl)
   {
   	int unlock = 0;
+	unsigned long flags;
 
   	BUG_ON(dl->dl_count == 0);
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
   	dl->dl_count--;
   	unlock = !dl->dl_count;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
   	if (unlock)
   		ocfs2_drop_dentry_lock(osb, dl);

fs/ocfs2/dlmglue.c +7 -7

index 4689940..9bff3d2 100644
@@ -3801,7 +3801,7 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   	struct ocfs2_dentry_lock *dl = ocfs2_lock_res_dl(lockres);
   	struct ocfs2_inode_info *oi = OCFS2_I(dl->dl_inode);
   	struct dentry *dentry;
-	unsigned long flags;
+	unsigned long flags, d_flags;
   	int extra_ref = 0;
 
   	/*

@@ -3831,13 +3831,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   	 * flag.
   	 */
   	spin_lock_irqsave(&lockres->l_lock, flags);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
   	if (!(lockres->l_flags & OCFS2_LOCK_FREEING)
   	    && dl->dl_count) {
   		dl->dl_count++;
   		extra_ref = 1;
   	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
   	spin_unlock_irqrestore(&lockres->l_lock, flags);
 
   	mlog(0, "extra_ref = %d\n", extra_ref);

@@ -3850,13 +3850,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   	if (!extra_ref)
   		return UNBLOCK_CONTINUE;
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
   	while (1) {
   		dentry = ocfs2_find_local_alias(dl->dl_inode,
   						dl->dl_parent_blkno, 1);
   		if (!dentry)
   			break;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
   		if (S_ISDIR(dl->dl_inode->i_mode))
   			shrink_dcache_parent(dentry);

@@ -3874,9 +3874,9 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
   		d_delete(dentry);
   		dput(dentry);
 
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, d_flags);
   	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
   	/*
   	 * If we are the last holder of this dentry lock, there is no

fs/ocfs2/namei.c +1 -0

index 3b0a10d..a17454e 100644
@@ -223,13 +223,14 @@ static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb,
   		struct dentry *dentry, struct inode *inode)
   {
   	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
   	ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);

fs/ocfs2/namei.c static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb, · line 236

Quoted 10 lines

fs/ocfs2/namei.c +2 -2

   	ocfs2_lock_res_free(&dl->dl_lockres);
   	BUG_ON(dl->dl_count != 1);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
   	dentry->d_fsdata = NULL;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
   	kfree(dl);
   	iput(inode);
   }

.

.

Hi Changwei,

Quoted 56 lines · Changwei Ge

Quoted 35 lines · piaojun

Hi Changwei,

Quoted 23 lines · Changwei Ge

Hi Jun,

Quoted 4 lines · piaojun

CPUA CPUB

ocfs2_dentry_convert_worker
get 'l_lock'

This lock belongs to ocfs2_dentry_lock::ocfs2_lock_res::l_lock

Quoted 12 lines

get 'dentry_attach_lock'

interruptted by dio_end_io:
dio_end_io
dio_bio_end_aio
dio_complete
dio->end_io
ocfs2_dio_end_io
ocfs2_rw_unlock
...
try to get 'l_lock'

Quoted 8 lines

This lock belongs to ocfs2_lock_res::l_lock though.

So I think they are totally two different locks. So making spin_lock to interruption safe is pointless.

Thanks,
Changwei

Quoted 5 lines

For the same lock, we need use spin_lock_irqsave to ensure irq-safe as you said. But the scenario described above is another kind of deadlock caused by two different locks which stuck each other. To avoid this 'ABBA' deadlock we need follow the rule that 'spin_lock_irqsave' should be called under 'spin_lock_irqsave'.

Hi Jun,
I'm not sure if you understood my concern?
I agree with that we should avoid ABBA dead lock scenario. But the dead lock scenario your sequence diagram is demonstrating doesn't even exist.

Because CPU A is holding lock _X1_ and waiting for _dentry_attach_lock_. meanwhile CPU B is holding lock _dentry_attach_lock_ and waiting for _X2_. No ABBA deadlock condition is met, CPU B will acquire lock _X2_ without being affected by CPU A.

In a nutshell, there are three locks(lock memory space) involved in your diagram rather than two.

Quoted 3 lines

Thanks,
Changwei

Sorry for misunderstanding your point, and I realize no deadlock would happen as these two 'l_lock' belong to different lockres. But I still suggest merging this patch, because this would reduce the risk of introducing new deadlock probably by programming.

thanks,
Jun

Quoted 161 lines

Quoted 158 lines

thanks,
Jun

Quoted 153 lines

Quoted 140 lines

but CPUA has got it.

try to get 'dentry_attach_lock',
but CPUB has got 'dentry_attach_lock', and would not release it.

so we need use spin_lock_irqsave for 'dentry_attach_lock' to prevent interruptted by softirq.

Signed-off-by Jun Piao <[email protected]>

Reviewed-by Alex Chen <[email protected]>

---
    fs/ocfs2/dcache.c  | 14 ++++++++------
    fs/ocfs2/dlmglue.c | 14 +++++++-------
    fs/ocfs2/namei.c   |  5 +++--
    3 files changed, 18 insertions(+), 15 deletions(-)

fs/ocfs2/dcache.c +8 -6

index 2903730..6555fbf 100644
@@ -230,6 +230,7 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
    	int ret;
    	struct dentry *alias;
    	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
    	trace_ocfs2_dentry_attach_lock(dentry->d_name.len, dentry->d_name.name,
    				       (unsigned long long)parent_blkno, dl);

@@ -309,10 +310,10 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
    	ocfs2_dentry_lock_res_init(dl, parent_blkno, inode);
 
    out_attach:
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
    	dentry->d_fsdata = dl;
    	dl->dl_count++;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
    	/*
    	 * This actually gets us our PRMODE level lock. From now on,

@@ -333,9 +334,9 @@ int ocfs2_dentry_attach_lock(struct dentry *dentry,
    	if (ret < 0 && !alias) {
    		ocfs2_lock_res_free(&dl->dl_lockres);
    		BUG_ON(dl->dl_count != 1);
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, flags);
    		dentry->d_fsdata = NULL;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, flags);
    		kfree(dl);
    		iput(inode);
    	}

@@ -379,13 +380,14 @@ void ocfs2_dentry_lock_put(struct ocfs2_super *osb,
    			   struct ocfs2_dentry_lock *dl)
    {
    	int unlock = 0;
+	unsigned long flags;
 
    	BUG_ON(dl->dl_count == 0);
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
    	dl->dl_count--;
    	unlock = !dl->dl_count;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
 
    	if (unlock)
    		ocfs2_drop_dentry_lock(osb, dl);

fs/ocfs2/dlmglue.c +7 -7

index 4689940..9bff3d2 100644
@@ -3801,7 +3801,7 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
    	struct ocfs2_dentry_lock *dl = ocfs2_lock_res_dl(lockres);
    	struct ocfs2_inode_info *oi = OCFS2_I(dl->dl_inode);
    	struct dentry *dentry;
-	unsigned long flags;
+	unsigned long flags, d_flags;
    	int extra_ref = 0;
 
    	/*

@@ -3831,13 +3831,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
    	 * flag.
    	 */
    	spin_lock_irqsave(&lockres->l_lock, flags);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
    	if (!(lockres->l_flags & OCFS2_LOCK_FREEING)
    	    && dl->dl_count) {
    		dl->dl_count++;
    		extra_ref = 1;
    	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
    	spin_unlock_irqrestore(&lockres->l_lock, flags);
 
    	mlog(0, "extra_ref = %d\n", extra_ref);

@@ -3850,13 +3850,13 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
    	if (!extra_ref)
    		return UNBLOCK_CONTINUE;
 
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, d_flags);
    	while (1) {
    		dentry = ocfs2_find_local_alias(dl->dl_inode,
    						dl->dl_parent_blkno, 1);
    		if (!dentry)
    			break;
-		spin_unlock(&dentry_attach_lock);
+		spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
    		if (S_ISDIR(dl->dl_inode->i_mode))
    			shrink_dcache_parent(dentry);

@@ -3874,9 +3874,9 @@ static int ocfs2_dentry_convert_worker(struct ocfs2_lock_res *lockres,
    		d_delete(dentry);
    		dput(dentry);
 
-		spin_lock(&dentry_attach_lock);
+		spin_lock_irqsave(&dentry_attach_lock, d_flags);
    	}
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, d_flags);
 
    	/*
    	 * If we are the last holder of this dentry lock, there is no

fs/ocfs2/namei.c +1 -0

index 3b0a10d..a17454e 100644
@@ -223,13 +223,14 @@ static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb,
    		struct dentry *dentry, struct inode *inode)
    {
    	struct ocfs2_dentry_lock *dl = dentry->d_fsdata;
+	unsigned long flags;
 
    	ocfs2_simple_drop_lockres(osb, &dl->dl_lockres);

fs/ocfs2/namei.c static void ocfs2_cleanup_add_entry_failure(struct ocfs2_super *osb, · line 236

Quoted 10 lines

fs/ocfs2/namei.c +2 -2

    	ocfs2_lock_res_free(&dl->dl_lockres);
    	BUG_ON(dl->dl_count != 1);
-	spin_lock(&dentry_attach_lock);
+	spin_lock_irqsave(&dentry_attach_lock, flags);
    	dentry->d_fsdata = NULL;
-	spin_unlock(&dentry_attach_lock);
+	spin_unlock_irqrestore(&dentry_attach_lock, flags);
    	kfree(dl);
    	iput(inode);
    }

.

.