[34-longterm 109/196] mmc: sdhci: Check mrq != NULL in sdhci_tasklet_finish

[Paul Gortmaker]

From: Chris Ball <cjb@xxxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit 0c9c99a765321104cc5f9c97f949382a9ba4927e upstream.

It seems that under certain circumstances the sdhci_tasklet_finish()
call can be entered with mrq set to NULL, causing the system to crash
with a NULL pointer de-reference.

Seen on S3C6410 system.  Based on a patch by Dimitris Papastamos.

Reported-by: Dimitris Papastamos <dp@xxxxxxxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Chris Ball <cjb@xxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 drivers/mmc/host/sdhci.c |    7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/mmc/host/sdhci.c b/drivers/mmc/host/sdhci.c
index 6441e22..be410d7 100644
--- a/drivers/mmc/host/sdhci.c
+++ b/drivers/mmc/host/sdhci.c
@@ -1268,6 +1268,13 @@ static void sdhci_tasklet_finish(unsigned long param)
 
 	host = (struct sdhci_host*)param;
 
+        /*
+         * If this tasklet gets rescheduled while running, it will
+         * be run again afterwards but without any active request.
+         */
+	if (!host->mrq)
+		return;
+
 	spin_lock_irqsave(&host->lock, flags);
 
 	del_timer(&host->timer);
-- 
1.7.9.3

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