linux-kernel - [BUG] usb: typec: ucsi: possible deadlock in ucsi_pr_swap() and ucsi_handle_connector

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Message-ID: <037de7ac-e210-bdf5-ec7a-8c0c88a0be20@gmail.com>
Date:   Wed, 9 Feb 2022 11:50:57 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     heikki.krogerus@...ux.intel.com,
        Greg KH <gregkh@...uxfoundation.org>, kyletso@...gle.com,
        jackp@...eaurora.org, andy.shevchenko@...il.com,
        unixbhaskar@...il.com, subbaram@...eaurora.org,
        mrana@...eaurora.org
Cc:     "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: [BUG] usb: typec: ucsi: possible deadlock in ucsi_pr_swap() and
 ucsi_handle_connector_change()

Hello,

My static analysis tool reports a possible deadlock in the ucsi driver 
in Linux 5.16:

ucsi_pr_swap()
   mutex_lock(&con->lock); --> Line 962 (Lock A)
   wait_for_completion_timeout(&con->complete, ...) --> Line 981 (Wait X)

ucsi_handle_connector_change()
   mutex_lock(&con->lock); --> Line 763 (Lock A)
   complete(&con->complete); --> Line 782 (Wake X)
   complete(&con->complete); --> Line 807 (Wake X)

When ucsi_pr_swap() is executed, "Wait X" is performed by holding "Lock 
A". If ucsi_handle_connector_change() is executed at this time, "Wake X" 
cannot be performed to wake up "Wait X" in 
ucsi_handle_connector_change(), because "Lock A" has been already held 
by ucsi_handle_connector_change(), causing a possible deadlock.
I find that "Wait X" is performed with a timeout, to relieve the 
possible deadlock; but I think this timeout can cause inefficient execution.

I am not quite sure whether this possible problem is real.
Any feedback would be appreciated, thanks :)

Best wishes,
Jia-Ju Bai