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authorKosuke Tatsukawa <tatsu@ab.jp.nec.com>2015-10-08 21:35:40 -0300
committerMauro Carvalho Chehab <mchehab@osg.samsung.com>2015-11-17 14:55:06 -0200
commit5063452ecb1c1c56b319d1b89b1b67c1abd849b9 (patch)
treebdcdc11f729dad5dd9751714954b1f72af87c232 /drivers/media/usb
parentdcc7fdbec53a960588f2c40232db2c6466c09917 (diff)
[media] media: fix waitqueue_active without memory barrier in cpia2 driver
cpia2_usb_disconnect() seems to be missing a memory barrier which might cause the waker to not notice the waiter and miss sending a wake_up as in the following figure. cpia2_usb_disconnect sync ------------------------------------------------------------------------ mutex_unlock(&cam->v4l2_lock); if (waitqueue_active(&cam->wq_stream)) /* The CPU might reorder the test for the waitqueue up here, before prior writes complete */ /* wait_event_interruptible */ /* __wait_event_interruptible */ /* ___wait_event */ long __int = prepare_to_wait_event( &wq, &__wait, state); if (!cam->streaming || frame->status == FRAME_READY) cam->curbuff->status = FRAME_READY; cam->curbuff->length = 0; schedule() ------------------------------------------------------------------------ The attached patch removes the call to waitqueue_active() leaving just wake_up() behind. This fixes the problem because the call to spin_lock_irqsave() in wake_up() will be an ACQUIRE operation. I found this issue when I was looking through the linux source code for places calling waitqueue_active() before wake_up*(), but without preceding memory barriers, after sending a patch to fix a similar issue in drivers/tty/n_tty.c (Details about the original issue can be found here: https://lkml.org/lkml/2015/9/28/849). Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Diffstat (limited to 'drivers/media/usb')
-rw-r--r--drivers/media/usb/cpia2/cpia2_usb.c3
1 files changed, 1 insertions, 2 deletions
diff --git a/drivers/media/usb/cpia2/cpia2_usb.c b/drivers/media/usb/cpia2/cpia2_usb.c
index 351a78a84c3d..c1aa1ab2ece9 100644
--- a/drivers/media/usb/cpia2/cpia2_usb.c
+++ b/drivers/media/usb/cpia2/cpia2_usb.c
@@ -890,8 +890,7 @@ static void cpia2_usb_disconnect(struct usb_interface *intf)
DBG("Wakeup waiting processes\n");
cam->curbuff->status = FRAME_READY;
cam->curbuff->length = 0;
- if (waitqueue_active(&cam->wq_stream))
- wake_up_interruptible(&cam->wq_stream);
+ wake_up_interruptible(&cam->wq_stream);
}
DBG("Releasing interface\n");

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