[PATCH v2] ipmi: Fix kernel panic at ipmi_ssif_thread()

[Joeseph Chang]

From: Joeseph Chang <joechang@xxxxxxxxxxxxxx>

Since patch v1 touch ssif_info->multi_pos and ssif_info->multi_data
after ssif_i2c_send(). msg_written_handler can be called at any time
after ssif_i2c_send(). There is possible to have concurrent access to
ssif_info->multi_pos or ssif_info->multi_data at msg_written_handler.

Revert patch v1 and add new local pointer "i2c_data" which point to
i2c data and size that will be sent out to avoid concurrent access in
msg_written_handler().

Signed-off-by: Joeseph Chang <joechang@xxxxxxxxxxxxxx>
---
 drivers/char/ipmi/ipmi_ssif.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
index 39346ee..f36f018 100644
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -852,6 +852,7 @@ static void msg_written_handler(struct ssif_info *ssif_info, int result,
 				unsigned char *data, unsigned int len)
 {
 	int rv;
+	unsigned char *i2c_data;
 
 	/* We are single-threaded here, so no need for a lock. */
 	if (result < 0) {
@@ -899,13 +900,22 @@ static void msg_written_handler(struct ssif_info *ssif_info, int result,
 			left = 32;
 		/* Length byte. */
 		ssif_info->multi_data[ssif_info->multi_pos] = left;
+		i2c_data = ssif_info->multi_data + ssif_info->multi_pos;
+		ssif_info->multi_pos += left;
+		if (left < 32)
+			/*
+			 * Write is finished.  Note that we must end
+			 * with a write of less than 32 bytes to
+			 * complete the transaction, even if it is
+			 * zero bytes.
+			 */
+			ssif_info->multi_data = NULL;
 
 		rv = ssif_i2c_send(ssif_info, msg_written_handler,
 				  I2C_SMBUS_WRITE,
 				  SSIF_IPMI_MULTI_PART_REQUEST_MIDDLE,
-				  ssif_info->multi_data + ssif_info->multi_pos,
+				  i2c_data,
 				  I2C_SMBUS_BLOCK_DATA);
-
 		if (rv < 0) {
 			/* request failed, just return the error. */
 			ssif_inc_stat(ssif_info, send_errors);
@@ -914,16 +924,6 @@ static void msg_written_handler(struct ssif_info *ssif_info, int result,
 				pr_info("Error from i2c_non_blocking_op(3)\n");
 			msg_done_handler(ssif_info, -EIO, NULL, 0);
 		}
-
-		ssif_info->multi_pos += left;
-		if (left < 32)
-			/*
-			 * Write is finished.  Note that we must end
-			 * with a write of less than 32 bytes to
-			 * complete the transaction, even if it is
-			 * zero bytes.
-			 */
-			ssif_info->multi_data = NULL;
 	} else {
 		/* Ready to request the result. */
 		unsigned long oflags, *flags;
-- 
1.9.1