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

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Message-ID: <YgPQB9BYJcDzbd02@kuha.fi.intel.com>
Date:   Wed, 9 Feb 2022 16:30:31 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, kyletso@...gle.com,
        jackp@...eaurora.org, andy.shevchenko@...il.com,
        unixbhaskar@...il.com, subbaram@...eaurora.org,
        mrana@...eaurora.org,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] usb: typec: ucsi: possible deadlock in ucsi_pr_swap() and
 ucsi_handle_connector_change()

On Wed, Feb 09, 2022 at 11:50:57AM +0800, Jia-Ju Bai wrote:
> 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 :)

This is probable a regression from commit ad74b8649bea ("usb: typec:
ucsi: Preliminary support for alternate modes"). Can you test does
this patch fix the issue (attached)?

thanks,

-- 
heikki

View attachment "0001-usb-typec-ucsi-Test-fix.patch" of type "text/plain" (1965 bytes)