Em 23-01-2012 14:23, Antti Palosaari escreveu:
> On 01/19/2012 03:31 PM, Mauro Carvalho Chehab wrote:
>> [PATCH] dvb-usb: Don't abort stop on -EAGAIN/-EINTR
>>
>> Note: this patch is not complete. if the DVB demux device is opened on
>> block mode, it should instead be returning -EAGAIN.
>>
>> Signed-off-by: Mauro Carvalho Chehab<mchehab@xxxxxxxxxx>
>>
>> diff --git a/drivers/media/dvb/dvb-usb/dvb-usb-dvb.c b/drivers/media/dvb/dvb-usb/dvb-usb-dvb.c
>> index ddf282f..215ce75 100644
>> --- a/drivers/media/dvb/dvb-usb/dvb-usb-dvb.c
>> +++ b/drivers/media/dvb/dvb-usb/dvb-usb-dvb.c
>> @@ -30,7 +30,9 @@ static int dvb_usb_ctrl_feed(struct dvb_demux_feed *dvbdmxfeed, int onoff)
>> usb_urb_kill(&adap->fe_adap[adap->active_fe].stream);
>>
>> if (adap->props.fe[adap->active_fe].streaming_ctrl != NULL) {
>> - ret = adap->props.fe[adap->active_fe].streaming_ctrl(adap, 0);
>> + do {
>> + ret = adap->props.fe[adap->active_fe].streaming_ctrl(adap, 0);
>> + } while ((ret == -EAGAIN) || (ret == -EINTR));
>> if (ret< 0) {
>> err("error while stopping stream.");
>> return ret;
>>
>
> That fixes it. But it loops do {...} while around 100 times every I stop zap. Over 100 times is rather much...
Yes, this sounds too much.
The issue here is caused by the usage of mutex_lock_interruptible() inside the
streaming_ctrl() callbacks, when the stream should stop.
The new wait_queue wakeup inside the code made the issue more visible, but it
could still happen without it, as a break could be hit during stream_ctl()
stop call anyway.
There are two possible fixes for it:
1) The above solution.
Eventually, a schedule() could be added there:
do {
ret = adap->props.fe[adap->active_fe].streaming_ctrl(adap, 0);
if (ret == -EINTR)
shedule();
} while (ret == -EINTR);
2)
Don't use mutex_lock_interruptible inside the driver's streaming_ctrl,
if the second parameter is 0 (stop).
IMHO, (1) is cleaner, due to a few reasons:
- inside the drivers, the code will be symmetrical: it will call the same function for
both onoff = 1 and onoff = 0.
- The patch is on just one place;
- with (2), extra care is needed when merging patches, as regressions and
broken drivers could pass unnoticed.
>
> And I think -EINTR is the only code to look, -EAGAIN is maybe for I2C and can be switched to native -EINTR also.
Drivers need to be checked, if only -EINTR is added there, as drivers may
be doing things like:
if (mutex_lock_interruptible(...))
return -EAGAIN;
Regards,
Mauro
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