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SubjectRe: [RFC/PATCH 0/3] locking fixes for cx88
Date
Jonathan Nieder <jrnieder <at> gmail.com> writes:

>
> Hi,
>
> Huber Andreas wrote[1]:
>
> > Processes that try to open a cx88-blackbird driven MPEG device will hang up.
>
> Here's a possible fix based on a patch by Ben Hutchings and
> corrections from Andi Huber. Warning: probably full of mistakes (my
> fault) since I'm not familiar with any of this stuff. Untested.
> Review and testing would be welcome.
>
> Ben Hutchings (2):
> [media] cx88: fix locking of sub-driver operations
> [media] cx88: use a mutex to protect cx8802_devlist
>
> Jonathan Nieder (1):
> [media] cx88: protect per-device driver list with device lock
>
> drivers/media/video/cx88/cx88-blackbird.c | 3 +-
> drivers/media/video/cx88/cx88-dvb.c | 2 +
> drivers/media/video/cx88/cx88-mpeg.c | 35 +++++++++++++++++++---------
> drivers/media/video/cx88/cx88.h | 10 +++++++-
> 4 files changed, 37 insertions(+), 13 deletions(-)
>

There is an unrelated issue!!!

The driver's active_ref count may become negative which leads to unpredictable
behavior. (MPEG video device inaccessible, etc ...)

Here's a possible fix ...


diff -Nur a/drivers/media/video/cx88/cx88-mpeg.c
b/drivers/media/video/cx88/cx88-mpeg.c
--- a/drivers/media/video/cx88/cx88-mpeg.c 2011-04-02 14:34:21.456569849 +0200
+++ b/drivers/media/video/cx88/cx88-mpeg.c 2011-04-02 14:32:55.467038000 +0200
@@ -642,12 +642,16 @@
{
struct cx88_core *core = drv->core;

+ mpeg_dbg(1,"%s active driver references before release attempt:
%d\n",core->name,core->active_ref);
+
if (drv->advise_release && --core->active_ref == 0)
{
drv->advise_release(drv);
core->active_type_id = CX88_BOARD_NONE;
mpeg_dbg(1,"%s() Post release GPIO=%x\n", __func__, cx_read(MO_GP0_IO));
}
+
+ if(core->active_ref<0) core->active_ref=0; // prevent us from getting negative
ref counts!

return 0;
}

I can confirm that Johnathan's patchset plus applying this fix works!
Tests done on amd64 hardware with 2 Hauppauge HVR1300 TV cards:
Both were independently able to tune channels and stream encoded video through
their MPEG encoder devices.

Andi.



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