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From: Wolfram Sang <wsa+renesas@sang-engineering.com>
To: linux-renesas-soc@vger.kernel.org
Cc: Wolfram Sang <wsa+renesas@sang-engineering.com>,
	Dirk Behme <dirk.behme@de.bosch.com>,
	stable@vger.kernel.org,
	Ulf Hansson <ulf.hansson@linaro.org>,
	Chris Ball <cjb@laptop.org>,
	Guennadi Liakhovetski <g.liakhovetski@gmx.de>,
	linux-mmc@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2] mmc: tmio: avoid concurrent runs of mmc_request_done()
Date: Tue,  5 Mar 2024 11:42:56 +0100
Message-ID: <20240305104423.3177-2-wsa+renesas@sang-engineering.com>
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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@de.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@sang-engineering.com>
Tested-by: Dirk Behme <dirk.behme@de.bosch.com>
Reviewed-by: Dirk Behme <dirk.behme@de.bosch.com>
Cc: stable@vger.kernel.org # 3.0+
---

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