linux-kernel - [PATCH] lockd: fix regression in lockd's handling of blocked locks

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Message-ID: <20090209182425.GJ10297@fieldses.org>
Date:	Mon, 9 Feb 2009 13:24:25 -0500
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...nel.org, Frank van Maarseveen <frankvm@...nkvm.com>,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: [PATCH] lockd: fix regression in lockd's handling of blocked locks

From: J. Bruce Fields <bfields@...i.umich.edu>

If a client requests a blocking lock, is denied, then requests it again,
then here in nlmsvc_lock() we will call vfs_lock_file() without FL_SLEEP
set, because we've already queued a block and don't need the locks code
to do it again.

But that means vfs_lock_file() will return -EAGAIN instead of
FILE_LOCK_DENIED.  So we still need to translate that -EAGAIN return
into a nlm_lck_blocked error in this case, and put ourselves back on
lockd's block list.

The bug was introduced by bde74e4bc64415b1 "locks: add special return
value for asynchronous locks".

Thanks to Frank van Maarseveen for the report; his original test
case was essentially

	for i in `seq 30`; do flock /nfsmount/foo sleep 10 & done

Tested-by: Frank van Maarseveen <frankvm@...nkvm.com>
Reported-by: Frank van Maarseveen <frankvm@...nkvm.com>
Cc: Miklos Szeredi <mszeredi@...e.cz>
Signed-off-by: J. Bruce Fields <bfields@...i.umich.edu>
---
 fs/lockd/svclock.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

Also available from

	git://linux-nfs.org/~bfields/linux.git for-2.6.29

Also appropriate for stable.--b.

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 6063a8e..763b78a 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -427,7 +427,7 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 			goto out;
 		case -EAGAIN:
 			ret = nlm_lck_denied;
-			goto out;
+			break;
 		case FILE_LOCK_DEFERRED:
 			if (wait)
 				break;
@@ -443,6 +443,10 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 			goto out;
 	}
 
+	ret = nlm_lck_denied;
+	if (!wait)
+		goto out;
+
 	ret = nlm_lck_blocked;
 
 	/* Append to list of blocked */
-- 
1.5.6.3

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