Hi Jonathan, thanks for locking into it.
I'll try to debug more deeply what's going wrong and keep you up to date.
Andi.
On 02.04.2011 21:29, Jonathan Nieder wrote:
Hi Andreas,
(please turn off HTML mail.)
Andreas Huber wrote:
There is a reference count bug in the driver code. The driver's
active_ref count may become negative which leads to unpredictable
behavior. (mpeg video device inaccessible, etc ...)
Hmm, the patchset didn't touch active_ref handling.
active_ref was added by v2.6.25-rc3~132^2~7 (V4L/DVB (7194):
cx88-mpeg: Allow concurrent access to cx88-mpeg devices, 2008-02-11)
and relies on three assumptions:
* (successful) calls to cx8802_driver::request_acquire are balanced
with calls to cx8802_driver::request_release;
* cx8802_driver::advise_acquire is non-null if and only if
cx8802_driver::advise_release is (since both are NULL for
blackbird, non-NULL for dvb);
* no data races.
I suppose it would be more idiomatic to use an atomic_t, but access to
active_ref was previously protected by the BKL and now it is protected
by core->lock. So it's not clear to me why this doesn't work.
Any hints? (e.g., a detailed reproduction recipe, or a log after
adding a printk to find out when exactly active_ref becomes negative)
Thanks for reporting.
Jonathan
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