linux-kernel - Re: [PATCH v2] mmc: tmio: avoid concurrent runs of mmc_request

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Message-ID: <CAPDyKFryGhRju5CohRipXk9E_G3kob2g8=VztjtPBZ_i6D9Ugw@mail.gmail.com>
Date: Tue, 5 Mar 2024 13:14:31 +0100
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: linux-renesas-soc@...r.kernel.org, Dirk Behme <dirk.behme@...bosch.com>, 
	stable@...r.kernel.org, Chris Ball <cjb@...top.org>, 
	Guennadi Liakhovetski <g.liakhovetski@....de>, linux-mmc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mmc: tmio: avoid concurrent runs of mmc_request_done()

On Tue, 5 Mar 2024 at 11:44, Wolfram Sang
<wsa+renesas@...g-engineering.com> wrote:
>
> With the to-be-fixed commit, the reset_work handler cleared 'host->mrq'
> outside of the spinlock protected critical section. That leaves a small
> race window during execution of 'tmio_mmc_reset()' where the done_work
> handler could grab a pointer to the now invalid 'host->mrq'. Both would
> use it to call mmc_request_done() causing problems (see link below).
>
> However, 'host->mrq' cannot simply be cleared earlier inside the
> critical section. That would allow new mrqs to come in asynchronously
> while the actual reset of the controller still needs to be done. So,
> like 'tmio_mmc_set_ios()', an ERR_PTR is used to prevent new mrqs from
> coming in but still avoiding concurrency between work handlers.
>
> Reported-by: Dirk Behme <dirk.behme@...bosch.com>
> Closes: https://lore.kernel.org/all/20240220061356.3001761-1-dirk.behme@de.bosch.com/
> Fixes: df3ef2d3c92c ("mmc: protect the tmio_mmc driver against a theoretical race")
> Signed-off-by: Wolfram Sang <wsa+renesas@...g-engineering.com>
> Tested-by: Dirk Behme <dirk.behme@...bosch.com>
> Reviewed-by: Dirk Behme <dirk.behme@...bosch.com>
> Cc: stable@...r.kernel.org # 3.0+

Applied for fixes, thanks!

Kind regards
Uffe


> ---
>
> Change since v1/RFT: added Dirk's tags and stable tag
>
> @Ulf: this is nasty, subtle stuff. Would be awesome to have it in 6.8
> already!
>
>  drivers/mmc/host/tmio_mmc_core.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/mmc/host/tmio_mmc_core.c b/drivers/mmc/host/tmio_mmc_core.c
> index be7f18fd4836..c253d176db69 100644
> --- a/drivers/mmc/host/tmio_mmc_core.c
> +++ b/drivers/mmc/host/tmio_mmc_core.c
> @@ -259,6 +259,8 @@ static void tmio_mmc_reset_work(struct work_struct *work)
>         else
>                 mrq->cmd->error = -ETIMEDOUT;
>
> +       /* No new calls yet, but disallow concurrent tmio_mmc_done_work() */
> +       host->mrq = ERR_PTR(-EBUSY);
>         host->cmd = NULL;
>         host->data = NULL;
>
> --
> 2.43.0
>