linux-kernel - [PATCH] cx18: Fix a sleep-in-atomic bug in snd_cx18_pcm_hw

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Message-Id: <1496301472-2754-1-git-send-email-baijiaju1990@163.com>
Date:   Thu,  1 Jun 2017 15:17:51 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     awalls@...metrocast.net, mchehab@...nel.org
Cc:     linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jia-Ju Bai <baijiaju1990@....com>
Subject: [PATCH] cx18: Fix a sleep-in-atomic bug in snd_cx18_pcm_hw_free

The driver may sleep under a spin lock, and the function call path is:
snd_cx18_pcm_hw_free (acquire the lock by spin_lock_irqsave)
  vfree --> may sleep

To fix it, the "substream->runtime->dma_area" is passed to a temporary
value, and mark it NULL when holding the lock. The memory is freed by
vfree through the temporary value outside the lock holding.

Signed-off-by: Jia-Ju Bai <baijiaju1990@....com>
---
 drivers/media/pci/cx18/cx18-alsa-pcm.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/media/pci/cx18/cx18-alsa-pcm.c b/drivers/media/pci/cx18/cx18-alsa-pcm.c
index 205a98d..8c51e4c 100644
--- a/drivers/media/pci/cx18/cx18-alsa-pcm.c
+++ b/drivers/media/pci/cx18/cx18-alsa-pcm.c
@@ -257,14 +257,17 @@ static int snd_cx18_pcm_hw_free(struct snd_pcm_substream *substream)
 {
 	struct snd_cx18_card *cxsc = snd_pcm_substream_chip(substream);
 	unsigned long flags;
+	unsigned char *dma_area = NULL;
 
 	spin_lock_irqsave(&cxsc->slock, flags);
 	if (substream->runtime->dma_area) {
 		dprintk("freeing pcm capture region\n");
-		vfree(substream->runtime->dma_area);
+		dma_area = substream->runtime->dma_area;
 		substream->runtime->dma_area = NULL;
 	}
 	spin_unlock_irqrestore(&cxsc->slock, flags);
+	if (dma_area)
+		vfree(dma_area);
 
 	return 0;
 }
-- 
1.7.9.5