linux-kernel - Re: [PATCH 1/2] USB: cdc-acm: fix racy tty buffer accesses

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Date:   Thu, 30 Sep 2021 11:04:19 +0200
From:   Oliver Neukum <oneukum@...e.com>
To:     Johan Hovold <johan@...nel.org>, Oliver Neukum <oneukum@...e.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] USB: cdc-acm: fix racy tty buffer accesses


On 29.09.21 11:09, Johan Hovold wrote:
> A recent change that started reporting break events to the line
> discipline caused the tty-buffer insertions to no longer be serialised
> by inserting events also from the completion handler for the interrupt
> endpoint.
>
> Completion calls for distinct endpoints are not guaranteed to be
> serialised. For example, in case a host-controller driver uses
> bottom-half completion, the interrupt and bulk-in completion handlers
> can end up running in parallel on two CPUs (high-and low-prio tasklets,
> respectively) thereby breaking the tty layer's single producer
> assumption.
>
> Fix this by holding the read lock also when inserting characters from
> the bulk endpoint.
>
> Fixes: 08dff274edda ("cdc-acm: fix BREAK rx code path adding necessary calls")
> Cc: stable@...r.kernel.org
> Signed-off-by: Johan Hovold <johan@...nel.org>
Acked-by: Oliver Neukum <oneukum@...e.com>