netdev - [PATCH] SUNRPC: prevent task_cleanup running on freed xprt

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Date:	Tue, 3 Aug 2010 17:22:20 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Jeff Layton <jlayton@...hat.com>, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org
Subject: [PATCH] SUNRPC: prevent task_cleanup running on freed xprt

From: J. Bruce Fields <bfields@...hat.com>

We saw a report of a NULL dereference in xprt_autoclose:

	https://bugzilla.redhat.com/show_bug.cgi?id=611938

This appears to be the result of an xprt's task_cleanup running after
the xprt is destroyed.  Nothing in the current code appears to prevent
that.

Signed-off-by: J. Bruce Fields <bfields@...hat.com>
---
 net/sunrpc/xprt.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

On Tue, Aug 03, 2010 at 02:49:23PM -0400, Trond Myklebust wrote:
> Hmm... On the other hand, since xprt_destroy() may get called from
> inside the rpciod_workqueue, the wait_on_bit_lock() may end up
> deadlocking.
> 
> Nevermind, then. Let's go with the cancel_work_sync().

Here you are--only if you don't have something equivalent already queued
up.--b.

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index dcd0132..2a1f664 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1129,6 +1129,7 @@ static void xprt_destroy(struct kref *kref)
 	rpc_destroy_wait_queue(&xprt->sending);
 	rpc_destroy_wait_queue(&xprt->resend);
 	rpc_destroy_wait_queue(&xprt->backlog);
+	cancel_work_sync(&xprt->task_cleanup);
 	/*
 	 * Tear down transport state and free the rpc_xprt
 	 */
-- 
1.7.0.4

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