linux-kernel - Re: [PATCH v2] i2c: bcm2835: Clear current buffer pointers and counts after a transfer

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Message-ID: <20190205120905.GB1045@kunai>
Date:   Tue, 5 Feb 2019 13:09:06 +0100
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     bcm-kernel-feedback-list@...adcom.com, linux-i2c@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Eric Anholt <eric@...olt.net>,
        Stefan Wahren <stefan.wahren@...e.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Eben Upton <eben@...pberrypi.org>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2] i2c: bcm2835: Clear current buffer pointers and
 counts after a transfer

On Thu, Dec 27, 2018 at 04:42:25PM +0100, Paul Kocialkowski wrote:
> The driver's interrupt handler checks whether a message is currently
> being handled with the curr_msg pointer. When it is NULL, the interrupt
> is considered to be unexpected. Similarly, the i2c_start_transfer
> routine checks for the remaining number of messages to handle in
> num_msgs.
> 
> However, these values are never cleared and always keep the message and
> number relevant to the latest transfer (which might be done already and
> the underlying message memory might have been freed).
> 
> When an unexpected interrupt hits with the DONE bit set, the isr will
> then try to access the flags field of the curr_msg structure, leading
> to a fatal page fault.
> 
> The msg_buf and msg_buf_remaining fields are also never cleared at the
> end of the transfer, which can lead to similar pitfalls.
> 
> Fix these issues by introducing a cleanup function and always calling
> it after a transfer is finished.
> 
> Fixes: e2474541032d ("i2c: bcm2835: Fix hang for writing messages larger than 16 bytes")
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>

Stefan, Florian, any comment about this patch?


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