Re: [PATCH] spi: core: Fix deadlock when sending messages

Jon Hunter
2016-03-08T09:50:31Z

Adding Vignesh ...

On 08/03/16 09:49, Jon Hunter wrote:
> The function __spi_pump_messages() is called by spi_pump_messages() and
> __spi_sync(). The function __spi_sync() has an argument 'bus_locked'
> that indicates if it is called with the SPI bus mutex held or not. If
> 'bus_locked' is false then __spi_sync() will acquire the mutex itself.
>
> Commit 556351f14e74 ("spi: introduce accelerated read support for spi
> flash devices") made a change to acquire the SPI bus mutex within
> __spi_pump_messages(). However, this change did not check to see if the
> mutex is already held. If __spi_sync() is called with the mutex held
> (ie. 'bus_locked' is true), then a deadlock occurs when
> __spi_pump_messages() is called.
>
> Fix this deadlock by passing the 'bus_locked' state from __spi_sync() to
> __spi_pump_messages() and only acquire the mutex if not already held. In
> the case where __spi_pump_messages() is called from spi_pump_messages()
> it is assumed that the mutex is not held and so call
> __spi_pump_messages() with 'bus_locked' set to false. Finally, move the
> unlocking of the mutex to the end of the __spi_pump_messages() function
> to simplify the code and only call cond_resched() if there are no
> errors.
>
> Fixes: 556351f14e74 ("spi: introduce accelerated read support for spi flash devices")
>
> Signed-off-by: Jon Hunter <jonathanh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org>
> ---
>
> This deadlock is seen on the Tegra124 Nyan Big chromebook and prevents
> the board from booting -next.
>
> drivers/spi/spi.c | 28 ++++++++++++++++------------
> 1 file changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> index fe0196328aa0..e699fec9ddc5 100644
> --- a/drivers/spi/spi.c
> +++ b/drivers/spi/spi.c
> @@ -1062,7 +1062,8 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
> * inside spi_sync(); the queue extraction handling at the top of the
> * function should deal with this safely.
> */
> -static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
> +static void __spi_pump_messages(struct spi_master *master, bool in_kthread,
> + bool bus_locked)
> {
> unsigned long flags;
> bool was_busy = false;
> @@ -1158,7 +1159,9 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
> }
> }
>
> - mutex_lock(&master->bus_lock_mutex);
> + if (!bus_locked)
> + mutex_lock(&master->bus_lock_mutex);
> +
> trace_spi_message_start(master->cur_msg);
>
> if (master->prepare_message) {
> @@ -1168,8 +1171,7 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
> "failed to prepare message: %d\n", ret);
> master->cur_msg->status = ret;
> spi_finalize_current_message(master);
> - mutex_unlock(&master->bus_lock_mutex);
> - return;
> + goto out;
> }
> master->cur_msg_prepared = true;
> }
> @@ -1178,21 +1180,23 @@ static void __spi_pump_messages(struct spi_master *master, bool in_kthread)
> if (ret) {
> master->cur_msg->status = ret;
> spi_finalize_current_message(master);
> - mutex_unlock(&master->bus_lock_mutex);
> - return;
> + goto out;
> }
>
> ret = master->transfer_one_message(master, master->cur_msg);
> if (ret) {
> dev_err(&master->dev,
> "failed to transfer one message from queue\n");
> - mutex_unlock(&master->bus_lock_mutex);
> - return;
> + goto out;
> }
> - mutex_unlock(&master->bus_lock_mutex);
> +
> +out:
> + if (!bus_locked)
> + mutex_unlock(&master->bus_lock_mutex);
>
> /* Prod the scheduler in case transfer_one() was busy waiting */
> - cond_resched();
> + if (!ret)
> + cond_resched();
> }
>
> /**
> @@ -1204,7 +1208,7 @@ static void spi_pump_messages(struct kthread_work *work)
> struct spi_master *master =
> container_of(work, struct spi_master, pump_messages);
>
> - __spi_pump_messages(master, true);
> + __spi_pump_messages(master, true, false);
> }
>
> static int spi_init_queue(struct spi_master *master)
> @@ -2814,7 +2818,7 @@ static int __spi_sync(struct spi_device *spi, struct spi_message *message,
> spi_sync_immediate);
> SPI_STATISTICS_INCREMENT_FIELD(&spi->statistics,
> spi_sync_immediate);
> - __spi_pump_messages(master, false);
> + __spi_pump_messages(master, false, bus_locked);
> }
>
> wait_for_completion(&done);
>
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