Em 01-04-2012 12:53, Steinar H. Gunderson escreveu: > From: "Steinar H. Gunderson" <sesse@xxxxxxxxxxxx> > > dvb_usercopy(), which is called on all ioctls, not only copies data to and from > userspace, but also takes a lock on the file descriptor, which means that only > one ioctl can run at a time. This means that if one thread of mumudvb is busy > trying to get, say, the SNR from the frontend (which can hang due to the issue > above), the CAM thread's ioctl(fd, CA_GET_SLOT_INFO, ...) will hang, even > though it doesn't need to communicate with the hardware at all. This obviously > requires a better fix, but I don't know the generic DVB layer well enough to > say what it is. Maybe it's some sort of remnant of from when all ioctl()s took > the BKL. Note that on UMP kernels without preemption, mutex_lock is to the best > of my knowledge a no-op, so these delay issues would not show up on non-SMP. > > Signed-off-by: Steinar H. Gunderson <sesse@xxxxxxxxxxxx> > --- > drivers/media/dvb/dvb-core/dvbdev.c | 2 -- > 1 file changed, 2 deletions(-) > > diff --git a/drivers/media/dvb/dvb-core/dvbdev.c b/drivers/media/dvb/dvb-core/dvbdev.c > index 00a6732..e1217f6 100644 > --- a/drivers/media/dvb/dvb-core/dvbdev.c > +++ b/drivers/media/dvb/dvb-core/dvbdev.c > @@ -417,10 +417,8 @@ int dvb_usercopy(struct file *file, > } > > /* call driver */ > - mutex_lock(&dvbdev_mutex); > if ((err = func(file, cmd, parg)) == -ENOIOCTLCMD) > err = -EINVAL; > - mutex_unlock(&dvbdev_mutex); As-is, this would be too risky, as it may break random drivers. A change like that would require to push down the mutex lock into each caller for dvb_user_copy: drivers/media/dvb/dvb-core/dmxdev.c: return dvb_usercopy(file, cmd, arg, dvb_demux_do_ioctl); drivers/media/dvb/dvb-core/dmxdev.c: return dvb_usercopy(file, cmd, arg, dvb_dvr_do_ioctl); drivers/media/dvb/dvb-core/dvb_ca_en50221.c: return dvb_usercopy(file, cmd, arg, dvb_ca_en50221_io_do_ioctl); drivers/media/dvb/dvb-core/dvb_net.c: return dvb_usercopy(file, cmd, arg, dvb_net_do_ioctl); drivers/media/dvb/dvb-core/dvbdev.c: return dvb_usercopy(file, cmd, arg, dvbdev->kernel_ioctl); drivers/media/dvb/dvb-core/dvbdev.c:int dvb_usercopy(struct file *file, drivers/media/dvb/dvb-core/dvbdev.h:we simply define out own dvb_usercopy(), which will hopefully become drivers/media/dvb/dvb-core/dvbdev.h:extern int dvb_usercopy(struct file *file, unsigned int cmd, unsigned long arg, $ git grep kernel_ioctl drivers/media/dvb/ drivers/media/dvb/dvb-core/dvb_frontend.c: .kernel_ioctl = dvb_frontend_ioctl drivers/media/dvb/dvb-core/dvbdev.c: if (!dvbdev->kernel_ioctl) drivers/media/dvb/dvb-core/dvbdev.c: return dvb_usercopy(file, cmd, arg, dvbdev->kernel_ioctl); drivers/media/dvb/dvb-core/dvbdev.h: int (*kernel_ioctl)(struct file *file, unsigned int cmd, void *arg); drivers/media/dvb/firewire/firedtv-ci.c: .kernel_ioctl = fdtv_ca_ioctl, drivers/media/dvb/ttpci/av7110.c: .kernel_ioctl = dvb_osd_ioctl, drivers/media/dvb/ttpci/av7110_av.c: .kernel_ioctl = dvb_video_ioctl, drivers/media/dvb/ttpci/av7110_av.c: .kernel_ioctl = dvb_audio_ioctl, drivers/media/dvb/ttpci/av7110_ca.c: .kernel_ioctl = dvb_ca_ioctl, And optimize the code there to avoid uneeded locks. > > if (err < 0) > goto out; -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
