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Message-Id: <20220418121211.327937970@linuxfoundation.org>
Date: Mon, 18 Apr 2022 14:10:03 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, NeilBrown <neilb@...e.de>,
Trond Myklebust <trond.myklebust@...merspace.com>
Subject: [PATCH 4.14 022/284] SUNRPC: avoid race between mod_timer() and del_timer_sync()
From: NeilBrown <neilb@...e.de>
commit 3848e96edf4788f772d83990022fa7023a233d83 upstream.
xprt_destory() claims XPRT_LOCKED and then calls del_timer_sync().
Both xprt_unlock_connect() and xprt_release() call
->release_xprt()
which drops XPRT_LOCKED and *then* xprt_schedule_autodisconnect()
which calls mod_timer().
This may result in mod_timer() being called *after* del_timer_sync().
When this happens, the timer may fire long after the xprt has been freed,
and run_timer_softirq() will probably crash.
The pairing of ->release_xprt() and xprt_schedule_autodisconnect() is
always called under ->transport_lock. So if we take ->transport_lock to
call del_timer_sync(), we can be sure that mod_timer() will run first
(if it runs at all).
Cc: stable@...r.kernel.org
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Trond Myklebust <trond.myklebust@...merspace.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
net/sunrpc/xprt.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1520,7 +1520,14 @@ static void xprt_destroy(struct rpc_xprt
*/
wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_UNINTERRUPTIBLE);
+ /*
+ * xprt_schedule_autodisconnect() can run after XPRT_LOCKED
+ * is cleared. We use ->transport_lock to ensure the mod_timer()
+ * can only run *before* del_time_sync(), never after.
+ */
+ spin_lock(&xprt->transport_lock);
del_timer_sync(&xprt->timer);
+ spin_unlock(&xprt->transport_lock);
/*
* Destroy sockets etc from the system workqueue so they can
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