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SUNRPC: avoid race between mod_timer() and del_timer_sync() 

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@vger.kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
This commit is contained in:
NeilBrown 2022-03-08 13:42:17 +11:00 committed by Trond Myklebust
parent a245832aaa
commit 3848e96edf
1 changed files with 7 additions and 0 deletions
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7
net/sunrpc/xprt.c
View File

@ -2104,7 +2104,14 @@ static void xprt_destroy(struct rpc_xprt *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