Ocfs2 devel - Dec 2015 - [PATCH] add OCFS2_LOCK_IGNORE_BLOCKED arg_flags to ocfs2_cluster_lock() to prevent hang

From: Linus Torvalds <torvalds at linux-foundation.org>

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 <tariq.x.saeed at oracle.com> Signed-off-by:
Junxiao Bi <junxiao.bi at oracle.com>
---
 Makefile           |    2 +-
 fs/ocfs2/acl.c     |    7 +++++--
 fs/ocfs2/dlmglue.c |    3 ++-
 fs/ocfs2/dlmglue.h |    2 ++
 4 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/Makefile b/Makefile
index 431067a..d5b3739 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 VERSION = 4
 PATCHLEVEL = 3
 SUBLEVEL = 0
-EXTRAVERSION = -rc7
+EXTRAVERSION  NAME = Blurry Fish Butt
 
 # *DOCUMENTATION*
diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
index 0cdf497..4404d9a 100644
--- a/fs/ocfs2/acl.c
+++ b/fs/ocfs2/acl.c
@@ -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);
diff --git a/fs/ocfs2/dlmglue.c b/fs/ocfs2/dlmglue.c
index 1c91103..ea79e1b 100644
--- a/fs/ocfs2/dlmglue.c
+++ b/fs/ocfs2/dlmglue.c
@@ -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);
diff --git a/fs/ocfs2/dlmglue.h b/fs/ocfs2/dlmglue.h
index d293a22..845831f 100644
--- a/fs/ocfs2/dlmglue.h
+++ b/fs/ocfs2/dlmglue.h
@@ -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,
-- 
1.7.1

On Tue, Dec 22, 2015 at 03:55:50PM -0800, Tariq Saeed
wrote:
> From: Linus Torvalds <torvalds at linux-foundation.org>
> 
> 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.

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

On 12/29/2015 04:34 PM, Mark Fasheh wrote:
> 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