spi: fix race freeing dummy_tx/rx before it is unmapped

Fix a race (with some kernel configurations) where a queued
master->pump_messages runs and frees dummy_tx/rx before
spi_unmap_msg is running (or is finished).

This results in the following messages:
  BUG: Bad page state in process
  page:db7ba030 count:0 mapcount:0 mapping:  (null) index:0x0
  flags: 0x200(arch_1)
  page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag set
  ...

Reported-by: Noralf Trønnes <noralf@tronnes.org>
Suggested-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org

1 files changed, 6 insertions, 5 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 50910d85df5a..d35c1a13217c 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -988,9 +988,6 @@ void spi_finalize_current_message(struct spi_master *master)
 
         spin_lock_irqsave(&master->queue_lock, flags);
         mesg = master->cur_msg;
-        master->cur_msg = NULL;
-
-        queue_kthread_work(&master->kworker, &master->pump_messages);
         spin_unlock_irqrestore(&master->queue_lock, flags);
 
         spi_unmap_msg(master, mesg);
@@ -1003,9 +1000,13 @@ void spi_finalize_current_message(struct spi_master *master)
                 }
         }
 
-        trace_spi_message_done(mesg);
-
+        spin_lock_irqsave(&master->queue_lock, flags);
+        master->cur_msg = NULL;
         master->cur_msg_prepared = false;
+        queue_kthread_work(&master->kworker, &master->pump_messages);
+        spin_unlock_irqrestore(&master->queue_lock, flags);
+
+        trace_spi_message_done(mesg);
 
         mesg->state = NULL;
         if (mesg->complete)