linux-kernel - [PATCH 1/2] rapidio/tsi721_dma: fix failure to obtain transaction descriptor

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Message-Id: <1406232191-4606-1-git-send-email-alexandre.bounine@idt.com>
Date:	Thu, 24 Jul 2014 16:03:10 -0400
From:	Alexandre Bounine <alexandre.bounine@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexandre Bounine <alexandre.bounine@....com>,
	Matt Porter <mporter@...nel.crashing.org>,
	Andre van Herk <andre.van.herk@...drive-technologies.com>,
	Stef van Os <stef.van.os@...drive-technologies.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	<linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>
Subject: [PATCH 1/2] rapidio/tsi721_dma: fix failure to obtain transaction descriptor

This is a bug fix for the situation when function tsi721_desc_get() fails
to obtain a free transaction descriptor.

The bug usually results in a memory access crash dump when data transfer
scatter-gather list has more entries than size of hardware buffer
descriptors ring. This fix ensures that error is properly returned to a caller
instead of an invalid entry.

This patch is applicable to kernel versions starting from v3.5.

Signed-off-by: Alexandre Bounine <alexandre.bounine@....com>
Cc: Matt Porter <mporter@...nel.crashing.org>
Cc: Andre van Herk <andre.van.herk@...drive-technologies.com>
Cc: Stef van Os <stef.van.os@...drive-technologies.com>
Cc: Vinod Koul <vinod.koul@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: <linux-kernel@...r.kernel.org>
Cc: <stable@...r.kernel.org>
---
 drivers/rapidio/devices/tsi721_dma.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/rapidio/devices/tsi721_dma.c b/drivers/rapidio/devices/tsi721_dma.c
index 9b60b1f..44341dc 100644
--- a/drivers/rapidio/devices/tsi721_dma.c
+++ b/drivers/rapidio/devices/tsi721_dma.c
@@ -287,6 +287,12 @@ struct tsi721_tx_desc *tsi721_desc_get(struct tsi721_bdma_chan *bdma_chan)
 			"desc %p not ACKed\n", tx_desc);
 	}
 
+	if (ret == NULL) {
+		dev_dbg(bdma_chan->dchan.device->dev,
+			"%s: unable to obtain tx descriptor\n", __func__);
+		goto err_out;
+	}
+
 	i = bdma_chan->wr_count_next % bdma_chan->bd_num;
 	if (i == bdma_chan->bd_num - 1) {
 		i = 0;
@@ -297,7 +303,7 @@ struct tsi721_tx_desc *tsi721_desc_get(struct tsi721_bdma_chan *bdma_chan)
 	tx_desc->txd.phys = bdma_chan->bd_phys +
 				i * sizeof(struct tsi721_dma_desc);
 	tx_desc->hw_desc = &((struct tsi721_dma_desc *)bdma_chan->bd_base)[i];
-
+err_out:
 	spin_unlock_bh(&bdma_chan->lock);
 
 	return ret;
-- 
1.7.11

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