linux-kernel - [PATCH 4.19 377/639] afs: Fix lock-wait/callback-break double locking

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Message-Id: <20200124093134.233102242@linuxfoundation.org>
Date:   Fri, 24 Jan 2020 10:29:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, David Howells <dhowells@...hat.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 377/639] afs: Fix lock-wait/callback-break double locking

From: David Howells <dhowells@...hat.com>

[ Upstream commit c7226e407b6065d3bda8bd9dc627663d2c505ea3 ]

__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>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 4ad7012502998..97283b04fa6fd 100644
--- a/fs/afs/callback.c
+++ b/fs/afs/callback.c
@@ -221,14 +221,8 @@ 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);
 	}
 
 	write_sequnlock(&vnode->cb_lock);
diff --git a/fs/afs/flock.c b/fs/afs/flock.c
index aea7224ba1981..fbf4986b12245 100644
--- a/fs/afs/flock.c
+++ b/fs/afs/flock.c
@@ -39,9 +39,6 @@ void afs_lock_may_be_available(struct afs_vnode *vnode)
 {
 	_enter("{%x:%u}", 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);
-- 
2.20.1