Kosuke Tatsukawa 5063452ecb [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>		2015-11-17 14:55:06 -02:00
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cpia2_core.c
cpia2_registers.h
cpia2_usb.c	[media] media: fix waitqueue_active without memory barrier in cpia2 driver	2015-11-17 14:55:06 -02:00
cpia2_v4l.c	[media] media: remove the setting of the flag V4L2_FL_USE_FH_PRIO	2014-07-04 16:14:59 -03:00
cpia2.h
Kconfig
Makefile