On Wed, Jun 28, 2023 at 03:19:51PM +0800, Tuo Li wrote: > The variable btv->loop_irq is often protected by the lock btv->s_lock when > is accessed. Here is an example in bttv_irq_timeout(): > > spin_lock_irqsave(&btv->s_lock,flags); > ... > btv->loop_irq = 0; > ... > spin_unlock_irqrestore(&btv->s_lock,flags); > > However, it is accessed without holding the lock btv->s_lock in > buffer_queue(): > > btv->loop_irq |= 1; > > And thus a data race can occur. > To fix this possible data race, a lock and unlock pair is added when > accessing the variable btv->loop_irq in buffer_queue(). hmm I am not sure why buffer_queue() didn't bother holding the btv->s_lock but in the new version of the bttv driver that I have been working on, the btv->s_lock is always held before changing the loop_irq value. https://patchwork.linuxtv.org/project/linux-media/cover/cover.1682995256.git.deborah.brouwer@xxxxxxxxxxxxx/ When the bttv driver is converted to vb2, and the work is almost done, the old buffer_queue() is totally eliminated, so I don't think it would make sense to apply this patch now. > > Reported-by: BassCheck <bass@xxxxxxxxxxx> > Signed-off-by: Tuo Li <islituo@xxxxxxxxx> > --- > drivers/media/pci/bt8xx/bttv-driver.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/media/pci/bt8xx/bttv-driver.c b/drivers/media/pci/bt8xx/bttv-driver.c > index 734f02b91aa3..241c51951627 100644 > --- a/drivers/media/pci/bt8xx/bttv-driver.c > +++ b/drivers/media/pci/bt8xx/bttv-driver.c > @@ -1617,13 +1617,16 @@ buffer_queue(struct videobuf_queue *q, struct videobuf_buffer *vb) > struct bttv_buffer *buf = container_of(vb,struct bttv_buffer,vb); > struct bttv_fh *fh = q->priv_data; > struct bttv *btv = fh->btv; > + unsigned long flags; > > + spin_lock_irqsave(&btv->s_lock,flags); > buf->vb.state = VIDEOBUF_QUEUED; > list_add_tail(&buf->vb.queue,&btv->capture); > if (!btv->curr.frame_irq) { > btv->loop_irq |= 1; > bttv_set_dma(btv, 0x03); > } > + spin_unlock_irqrestore(&btv->s_lock,flags); > } > > static void buffer_release(struct videobuf_queue *q, struct videobuf_buffer *vb) > -- > 2.34.1 >
