[PATCH 3.19.y-ckt 029/251] spi: fix race freeing dummy_tx/rx before it is unmapped

[Kamal Mostafa]

3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Martin Sperl <kernel at martin.sperl.org>

commit 8e76ef88f607174082023f50b87fe12dcdbe5db5 upstream.

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 at tronnes.org>
Suggested-by: Noralf Trønnes <noralf at tronnes.org>
Tested-by: Noralf Trønnes <noralf at tronnes.org>
Signed-off-by: Martin Sperl <kernel at martin.sperl.org>
Signed-off-by: Mark Brown <broonie at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/spi/spi.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index a17f533..bfa47d5 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1059,9 +1059,6 @@ 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);
@@ -1074,9 +1071,13 @@ 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)
-- 
1.9.1