linux-kernel - Re: [PATCH v5] staging: iio: adc: ad7816: fix race condition in SPI operations

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Message-ID: <aLX4SmvqBjJrS3FS@stanley.mountain>
Date: Mon, 1 Sep 2025 22:47:22 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Mohammad Amin Hosseini <moahmmad.hosseinii@...il.com>
Cc: linux-iio@...r.kernel.org, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org, gregkh@...uxfoundation.org,
	jic23@...nel.org, lars@...afoo.de, Michael.Hennerich@...log.com,
	dlechner@...libre.com, nuno.sa@...log.com, andy@...nel.org,
	sonic.zhang@...log.com, vapier@...too.org
Subject: Re: [PATCH v5] staging: iio: adc: ad7816: fix race condition in SPI
 operations

On Mon, Sep 01, 2025 at 11:10:43PM +0330, Mohammad Amin Hosseini wrote:
> The ad7816 driver lacks proper synchronization around SPI operations
> and device state access. Concurrent access from multiple threads can
> lead to data corruption and inconsistent device state.
> 
> The driver performs sequences of GPIO pin manipulations followed by
> SPI transactions without any locking. Device state variables (mode,
> channel_id, oti_data) are also accessed without synchronization.
> 
> This bug was found through manual code review using static analysis
> techniques. The review focused on identifying unsynchronized access
> patterns to shared resources. Key indicators were:
> - GPIO pin state changes followed by SPI operations without atomicity
> - Shared state variables accessed from multiple sysfs entry points
> - No mutex or spinlock protection around sections
> - Potential for interleaved execution in multi-threaded environments
> 
> The review methodology involved tracing data flow paths and identifying
> points where concurrent access could corrupt device state or SPI
> communication sequences.
> 
> Add io_lock mutex to protect:
> - SPI transactions and GPIO sequences in read/write functions
> - Device state variables in sysfs show/store functions
> - Concurrent access to chip configuration
> 
> This prevents race conditions when multiple processes access the device
> simultaneously through sysfs attributes or device file operations.
> 
> Fixes: 7924425db04a ("staging: iio: adc: new driver for AD7816 devices")
> 
> Signed-off-by: Mohammad Amin Hosseini <moahmmad.hosseinii@...il.com>
> 

I've asked you to wait a day between resends and Jonathan asked you to
wait for "a few days"...  It really is a headache to review the same
patch over and over in the same day.

regards,
dan carpenter