Skip to contentSkip to conversation

add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

PATCH New Tariq Saeed 4 participants 7 messages Dec 22, 2015 – Jan 6, 2016

Subsystems (2)
Kbuild OCFS2
lore
Share & tools
lore

Tariq Saeed

author
#0 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

From: Linus Torvalds <[email protected]>

Orabug: 21793017

commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()") introduced this issue. ocfs2_setattr called by chmod command holds cluster wide inode lock (Orabug 21685187) when calling posix_acl_chmod. This latter function in turn calls ocfs2_iop_get_acl and ocfs2_iop_set_acl. These two are also called directly from vfs layer for getfacl/setfacl commands and therefore acquire the cluster wide inode lock. If a remote conversion request comes after the first inode lock in ocfs2_setattr, OCFS2_LOCK_BLOCKED will be set in l_flags. This will cause the second call to inode lock from the ocfs2_iop_get|set_acl() to block indefinetly. The new flag OCFS2_LOCK_IGNORE_BLOCKED will be used to prevent this blocking.

Signed-off-by Tariq Saeed <[email protected]> Signed-off-by:

Junxiao Bi <[email protected]>

---
 Makefile           |    2 +-
 fs/ocfs2/acl.c     |    7 +++++--
 fs/ocfs2/dlmglue.c |    3 ++-
 fs/ocfs2/dlmglue.h |    2 ++
 4 files changed, 10 insertions(+), 4 deletions(-)
Makefile +1 -1
index 431067a..d5b3739 100644
@@ -1,7 +1,7 @@
 VERSION = 4
 PATCHLEVEL = 3
 SUBLEVEL = 0
-EXTRAVERSION = -rc7
+EXTRAVERSION =
 NAME = Blurry Fish Butt
 
 # *DOCUMENTATION*
fs/ocfs2/acl.c +5 -2
index 0cdf497..4404d9a 100644
@@ -37,6 +37,7 @@
 #include "xattr.h"
 #include "acl.h"
 
+
 /*
  * Convert from xattr value to acl struct.
  */

@@ -287,7 +288,8 @@ int ocfs2_iop_set_acl(struct inode *inode, struct posix_acl *acl, int type)
 	struct buffer_head *bh = NULL;
 	int status = 0;
 
-	status = ocfs2_inode_lock(inode, &bh, 1);
+	status = ocfs2_inode_lock_full(inode, &bh, 1,
+					OCFS2_LOCK_IGNORE_BLOCKED);
 	if (status < 0) {
 		if (status != -ENOENT)
 			mlog_errno(status);

@@ -309,7 +311,8 @@ struct posix_acl *ocfs2_iop_get_acl(struct inode *inode, int type)
 	osb = OCFS2_SB(inode->i_sb);
 	if (!(osb->s_mount_opt & OCFS2_MOUNT_POSIX_ACL))
 		return NULL;
-	ret = ocfs2_inode_lock(inode, &di_bh, 0);
+	ret = ocfs2_inode_lock_full(inode, &di_bh, 0,
+					OCFS2_LOCK_IGNORE_BLOCKED);
 	if (ret < 0) {
 		if (ret != -ENOENT)
 			mlog_errno(ret);
fs/ocfs2/dlmglue.c +2 -1
index 1c91103..ea79e1b 100644
@@ -1447,7 +1447,8 @@ again:
 	}
 
 	if (lockres->l_flags & OCFS2_LOCK_BLOCKED &&
-	    !ocfs2_may_continue_on_blocked_lock(lockres, level)) {
+	    !ocfs2_may_continue_on_blocked_lock(lockres, level) &&
+	    !(arg_flags & OCFS2_LOCK_IGNORE_BLOCKED)) {
 		/* is the lock is currently blocked on behalf of
 		 * another node */
 		lockres_add_mask_waiter(lockres, &mw, OCFS2_LOCK_BLOCKED, 0);
fs/ocfs2/dlmglue.h +2 -0
index d293a22..845831f 100644
@@ -78,6 +78,8 @@ struct ocfs2_orphan_scan_lvb {
 /* don't block waiting for the downconvert thread, instead return -EAGAIN */
 #define OCFS2_LOCK_NONBLOCK		(0x04)
 
+/* if requested level is <= l_level, ignore BLOCKED flag. */
+#define OCFS2_LOCK_IGNORE_BLOCKED		(0x08)
 /* Locking subclasses of inode cluster lock */
 enum {
 	OI_LS_NORMAL = 0,
Signature · 1 line
1.7.1
NAK
#1 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

Quoted 4 lines · Tariq Saeed

From: Linus Torvalds <[email protected]>

Orabug: 21793017

Quoted 11 lines

commit 743b5f1434f5 ("ocfs2: take inode lock in ocfs2_iop_set/get_acl()") introduced this issue. ocfs2_setattr called by chmod command holds cluster wide inode lock (Orabug 21685187) when calling posix_acl_chmod. This latter function in turn calls ocfs2_iop_get_acl and ocfs2_iop_set_acl. These two are also called directly from vfs layer for getfacl/setfacl commands and therefore acquire the cluster wide inode lock. If a remote conversion request comes after the first inode lock in ocfs2_setattr, OCFS2_LOCK_BLOCKED will be set in l_flags. This will cause the second call to inode lock from the ocfs2_iop_get|set_acl() to block indefinetly. The new flag OCFS2_LOCK_IGNORE_BLOCKED will be used to prevent this blocking.

NACK - as I explained earlier on this list we need to refactor the code to avoid double locking the same resource. It is not acceptable to introduce recursive locks into the code.

	--Mark

--
Mark Fasheh

author
#2 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

Quoted 1 line · Mark Fasheh

NACK - as I explained earlier on this list we need to refactor the code to

Not sure how things work in the open source world. Is refactoring to be picked by
somebody soon?
Thanks
-Tariq

#3 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

Quoted 6 lines · Tariq Saeed
Quoted 1 line · Mark Fasheh

NACK - as I explained earlier on this list we need to refactor the code to

Not sure how things work in the open source world. Is refactoring to be picked by
somebody soon?

No problem, A couple explanations / notes:

1) CC me with your patches (someone had to point the last one out to me).

I'll get to reviewing most things but if you CC me then it can happen sooner.

2) You are fixing the bug and sending the patches. We usually expect the sender to incorporate feedback into their patch so the answer would be that you get to to the refactoring :)

If you need to make small changes to the VFS to let this happen (sometimes we might want 'nolock' variants of funtions, etc), do them in seperate patches and send them along with your changes.

Hope this helps,

	--Mark

--
Mark Fasheh

#4 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

Hi Mark,

We may fix this issue in another way, without recursive locking and without refactoring. We can check before asking for the second locking, if lock is already hold, then skip the second locking, do you agree fixing like this?

Thanks,
Junxiao.

Quoted 35 lines · Mark Fasheh
Quoted 6 lines · Tariq Saeed
Quoted 1 line · Mark Fasheh

NACK - as I explained earlier on this list we need to refactor the code to

Not sure how things work in the open source world. Is refactoring to be picked by
somebody soon?

No problem, A couple explanations / notes:

1) CC me with your patches (someone had to point the last one out to me).

I'll get to reviewing most things but if you CC me then it can happen sooner.

2) You are fixing the bug and sending the patches. We usually expect the sender to incorporate feedback into their patch so the answer would be that you get to to the refactoring :)

If you need to make small changes to the VFS to let this happen (sometimes we might want 'nolock' variants of funtions, etc), do them in seperate patches and send them along with your changes.

Hope this helps,

	--Mark

--
Mark Fasheh

_______________________________________________
Ocfs2-devel mailing list
Ocfs2-devel at oss.oracle.com
https://oss.oracle.com/mailman/listinfo/ocfs2-devel

maintainer
#5 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

Quoted 6 lines · Junxiao Bi

Hi Mark,

We may fix this issue in another way, without recursive locking and without refactoring. We can check before asking for the second locking, if lock is already hold, then skip the second locking, do you agree fixing like this?

Hey Junxiao,

What is to prevent the second lock from being dropped while in the middle of the operation?

Joel

#6 lore raw

PATCH 1/1 add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

Hi Joel,

Quoted 8 lines · Joel Becker
Quoted 6 lines · Junxiao Bi

Hi Mark,

We may fix this issue in another way, without recursive locking and without refactoring. We can check before asking for the second locking, if lock is already hold, then skip the second locking, do you agree fixing like this?

Quoted 4 lines

Hey Junxiao,

What is to prevent the second lock from being dropped while in the middle of the operation?

Log processes id into lockres when lock is got. When do second locking, if this lock is already got by this process, then skip it.

Thanks,
Junxiao.

Quoted 3 lines

Joel