SUNRPC: avoid race between mod_timer() and del_timer_sync()
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@vger.kernel.org Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1446,7 +1446,14 @@ static void xprt_destroy(struct rpc_xprt *xprt)
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/* Exclude transport connect/disconnect handlers */
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wait_on_bit_lock(&xprt->state, XPRT_LOCKED, TASK_UNINTERRUPTIBLE);
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/*
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* xprt_schedule_autodisconnect() can run after XPRT_LOCKED
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* is cleared. We use ->transport_lock to ensure the mod_timer()
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* can only run *before* del_time_sync(), never after.
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*/
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spin_lock(&xprt->transport_lock);
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del_timer_sync(&xprt->timer);
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spin_unlock(&xprt->transport_lock);
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rpc_xprt_debugfs_unregister(xprt);
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rpc_destroy_wait_queue(&xprt->binding);
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