linux-kernel - [PATCH 14/15] afs: Fix lock-wait/callback-break double locking

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Date:   Wed, 15 May 2019 17:27:18 +0100
From:   David Howells <dhowells@...hat.com>
To:     linux-afs@...ts.infradead.org
Cc:     dhowells@...hat.com, linux-kernel@...r.kernel.org
Subject: [PATCH 14/15] afs: Fix lock-wait/callback-break double locking

__afs_break_callback() holds vnode->lock around its call of
afs_lock_may_be_available() - which also takes that lock.

Fix this by not taking the lock in __afs_break_callback().

Also, there's no point checking the granted_locks and pending_locks queues;
it's sufficient to check lock_state, so move that check out of
afs_lock_may_be_available() into __afs_break_callback() to replace the
queue checks.

Fixes: e8d6c554126b ("AFS: implement file locking")
Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/afs/callback.c |    8 +-------
 fs/afs/flock.c    |    3 ---
 2 files changed, 1 insertion(+), 10 deletions(-)

diff --git a/fs/afs/callback.c b/fs/afs/callback.c
index 128f2dbe256a..4876079aa643 100644
--- a/fs/afs/callback.c
+++ b/fs/afs/callback.c
@@ -218,14 +218,8 @@ void __afs_break_callback(struct afs_vnode *vnode)
 		vnode->cb_break++;
 		afs_clear_permits(vnode);
 
-		spin_lock(&vnode->lock);
-
-		_debug("break callback");
-
-		if (list_empty(&vnode->granted_locks) &&
-		    !list_empty(&vnode->pending_locks))
+		if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
 			afs_lock_may_be_available(vnode);
-		spin_unlock(&vnode->lock);
 	}
 }
 
diff --git a/fs/afs/flock.c b/fs/afs/flock.c
index 3501ef7ddbb4..c91cd201013f 100644
--- a/fs/afs/flock.c
+++ b/fs/afs/flock.c
@@ -41,9 +41,6 @@ void afs_lock_may_be_available(struct afs_vnode *vnode)
 {
 	_enter("{%llx:%llu}", vnode->fid.vid, vnode->fid.vnode);
 
-	if (vnode->lock_state != AFS_VNODE_LOCK_WAITING_FOR_CB)
-		return;
-
 	spin_lock(&vnode->lock);
 	if (vnode->lock_state == AFS_VNODE_LOCK_WAITING_FOR_CB)
 		afs_next_locker(vnode, 0);