linux-kernel - [BUG] iio: light: opt3001: possible deadlock in opt3001_read_raw() and opt3001

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Date:   Mon, 7 Feb 2022 23:41:49 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     jic23@...nel.org, lars@...afoo.de, valek@...cz,
        gwendal@...omium.org
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [BUG] iio: light: opt3001: possible deadlock in opt3001_read_raw()
 and opt3001_irq()

Hello,

My static analysis tool reports a possible deadlock in the opt3001 
driver in Linux 5.16:

opt3001_read_raw()
   mutex_lock(&opt->lock); --> Line 399 (Lock A)
   opt3001_get_lux()
     wait_event_timeout(opt->result_ready_queue, ...) --> Line 276 (Wait X)
   mutex_lock(&opt->lock); --> Line 412 (Unlock A)

opt3001_irq()
   mutex_lock(&opt->lock); --> Line 693 (Lock A)
   mutex_unlock(&opt->lock); --> Line 730 (Unlock A)
   wake_up(&opt->result_ready_queue); --> Line 733 (Wake X)

When opt3001_read_raw() is executed, "Wait X" is performed by holding 
"Lock A". If opt3001_irq() is executed at this time, "Wake X" cannot be 
performed to wake up "Wait X" in opt3001_read_raw(), because "Lock A" 
has been already hold by opt3001_read_raw(), 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 and how to fix 
it if it is real.
Any feedback would be appreciated, thanks :)

Best wishes,
Jia-Ju Bai