Re: mplayer v4l hangs in (likely regression)

From: Arjan van de Ven
Date: Tue May 20 2008 - 12:54:21 EST

On Tue, 20 May 2008 08:49:11 -0300
Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx> wrote:

> > Mauro: will you send this on to Linus or should this go direct?
> The fix looks sane. I prefer to just remove the lock call from bttv,
> instead of calling __videobuf_mmap_setup() and make this symbol
> global. The better is to avoid locking inside the drivers, except
> during the interrupts, and inside videbuf code. This is what we're
> doing on the other drivers.
> So, it would be better if you could change your patch to remove the
> lock/unlock at bttv-driver handling for this ioctl.

but it's more complex than I want to deal with right now.. lets changing
the locking in .27 instead rather than during an -rc
> To solve the bug, both ways work, so:
> Acked-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx>
> Could you please send it to Linus and to -stable for me? Otherwise,
> I'll do this by Monday.


Linus, please apply this bugfix:

From: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
Subject: [PATCH] Fix a deadlock in the bttv driver

vidiocgmbuf() does this:
retval = videobuf_mmap_setup(&fh->cap, gbuffers, gbufsize,

and videobuf_mmap_setup() then just does
ret = __videobuf_mmap_setup(q, bcount, bsize, memory);

which is an obvious double-take deadlock.

This patch fixes this by having vidiocgmbuf() just call the __videobuf_mmap_setup
function instead.

Acked-by: Mauro Carvalho Chehab <mchehab@xxxxxxxxxxxxx>
Reported-by: Koos Vriezen <koos.vriezen@xxxxxxxxx>
Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
drivers/media/video/bt8xx/bttv-driver.c | 2 +-
drivers/media/video/videobuf-core.c | 3 ++-
include/media/videobuf-core.h | 3 +++
3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/media/video/bt8xx/bttv-driver.c b/drivers/media/video/bt8xx/bttv-driver.c
index 2ca3e9c..0165aac 100644
--- a/drivers/media/video/bt8xx/bttv-driver.c
+++ b/drivers/media/video/bt8xx/bttv-driver.c
@@ -2613,7 +2613,7 @@ static int vidiocgmbuf(struct file *file, void *priv, struct video_mbuf *mbuf)
struct bttv_fh *fh = priv;

- retval = videobuf_mmap_setup(&fh->cap, gbuffers, gbufsize,
+ retval = __videobuf_mmap_setup(&fh->cap, gbuffers, gbufsize,
if (retval < 0) {
diff --git a/drivers/media/video/videobuf-core.c b/drivers/media/video/videobuf-core.c
index 982f446..0a88c44 100644
--- a/drivers/media/video/videobuf-core.c
+++ b/drivers/media/video/videobuf-core.c
@@ -331,7 +331,7 @@ int videobuf_mmap_free(struct videobuf_queue *q)

/* Locking: Caller holds q->vb_lock */
-static int __videobuf_mmap_setup(struct videobuf_queue *q,
+int __videobuf_mmap_setup(struct videobuf_queue *q,
unsigned int bcount, unsigned int bsize,
enum v4l2_memory memory)
@@ -1129,6 +1129,7 @@ EXPORT_SYMBOL_GPL(videobuf_read_stream);

diff --git a/include/media/videobuf-core.h b/include/media/videobuf-core.h
index 5b39a22..874f134 100644
--- a/include/media/videobuf-core.h
+++ b/include/media/videobuf-core.h
@@ -237,6 +237,9 @@ unsigned int videobuf_poll_stream(struct file *file,
int videobuf_mmap_setup(struct videobuf_queue *q,
unsigned int bcount, unsigned int bsize,
enum v4l2_memory memory);
+int __videobuf_mmap_setup(struct videobuf_queue *q,
+ unsigned int bcount, unsigned int bsize,
+ enum v4l2_memory memory);
int videobuf_mmap_free(struct videobuf_queue *q);
int videobuf_mmap_mapper(struct videobuf_queue *q,
struct vm_area_struct *vma);

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