spi: core: Fix deadlock when sending messages

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@nvidia.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 17 insertions, 12 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 0b2bbf144460..f565cc8901a6 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1047,6 +1047,7 @@ EXPORT_SYMBOL_GPL(spi_finalize_current_transfer);
  * __spi_pump_messages - function which processes spi message queue
  * @master: master to process queue for
  * @in_kthread: true if we are in the context of the message pump thread
+ * @bus_locked: true if the bus mutex is held when calling this function
  *
  * This function checks if there is any spi message in the queue that
  * needs processing and if so call out to the driver to initialize hardware
@@ -1056,7 +1057,8 @@ 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;
@@ -1152,7 +1154,9 @@ 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) {
@@ -1162,8 +1166,7 @@ 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;
         }
@@ -1172,21 +1175,23 @@ 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();
 }
 
 /**
@@ -1198,7 +1203,7 @@ 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)
@@ -2462,7 +2467,7 @@ 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);