| Message ID | 1388664474-1710039-8-git-send-email-arnd@arndb.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Arnd! On 01/02/2014 01:07 PM, Arnd Bergmann wrote: > interruptible_sleep_on is racy and going away. This replaces > one use in the radio-cadet driver with an open-coded > wait loop that lets us check the condition under the mutex > but sleep without it. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > Cc: Hans Verkuil <hverkuil@xs4all.nl> > Cc: Mauro Carvalho Chehab <m.chehab@samsung.com> > Cc: linux-media@vger.kernel.org > --- > drivers/media/radio/radio-cadet.c | 12 ++++++++++-- > 1 file changed, 10 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/radio/radio-cadet.c b/drivers/media/radio/radio-cadet.c > index 545c04c..67b5bbf 100644 > --- a/drivers/media/radio/radio-cadet.c > +++ b/drivers/media/radio/radio-cadet.c > @@ -39,6 +39,7 @@ > #include <linux/pnp.h> > #include <linux/sched.h> > #include <linux/io.h> /* outb, outb_p */ > +#include <linux/wait.h> > #include <media/v4l2-device.h> > #include <media/v4l2-ioctl.h> > #include <media/v4l2-ctrls.h> > @@ -323,25 +324,32 @@ static ssize_t cadet_read(struct file *file, char __user *data, size_t count, lo > struct cadet *dev = video_drvdata(file); > unsigned char readbuf[RDS_BUFFER]; > int i = 0; > + DEFINE_WAIT(wait); > > mutex_lock(&dev->lock); > if (dev->rdsstat == 0) > cadet_start_rds(dev); > - if (dev->rdsin == dev->rdsout) { > + while (1) { > + prepare_to_wait(&dev->read_queue, &wait, TASK_INTERRUPTIBLE); > + if (dev->rdsin != dev->rdsout) > + break; > + > if (file->f_flags & O_NONBLOCK) { > i = -EWOULDBLOCK; > goto unlock; > } > mutex_unlock(&dev->lock); > - interruptible_sleep_on(&dev->read_queue); > + schedule(); > mutex_lock(&dev->lock); > } > + This seems overly complicated. Isn't it enough to replace interruptible_sleep_on by 'wait_event_interruptible(&dev->read_queue, dev->rdsin != dev->rdsout);'? Or am I missing something subtle? Regards, Hans > while (i < count && dev->rdsin != dev->rdsout) > readbuf[i++] = dev->rdsbuf[dev->rdsout++]; > > if (i && copy_to_user(data, readbuf, i)) > i = -EFAULT; > unlock: > + finish_wait(&dev->read_queue, &wait); > mutex_unlock(&dev->lock); > return i; > } > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Friday 17 January 2014, Hans Verkuil wrote: > > @@ -323,25 +324,32 @@ static ssize_t cadet_read(struct file *file, char __user *data, size_t count, lo > > struct cadet *dev = video_drvdata(file); > > unsigned char readbuf[RDS_BUFFER]; > > int i = 0; > > + DEFINE_WAIT(wait); > > > > mutex_lock(&dev->lock); > > if (dev->rdsstat == 0) > > cadet_start_rds(dev); > > - if (dev->rdsin == dev->rdsout) { > > + while (1) { > > + prepare_to_wait(&dev->read_queue, &wait, TASK_INTERRUPTIBLE); > > + if (dev->rdsin != dev->rdsout) > > + break; > > + > > if (file->f_flags & O_NONBLOCK) { > > i = -EWOULDBLOCK; > > goto unlock; > > } > > mutex_unlock(&dev->lock); > > - interruptible_sleep_on(&dev->read_queue); > > + schedule(); > > mutex_lock(&dev->lock); > > } > > + > > This seems overly complicated. Isn't it enough to replace interruptible_sleep_on > by 'wait_event_interruptible(&dev->read_queue, dev->rdsin != dev->rdsout);'? > > Or am I missing something subtle? The existing code sleeps with &dev->lock released because the cadet_handler() function needs to grab (and release) the same lock before it can wake up the reader thread. Doing the simple wait_event_interruptible() would result in a deadlock here. Arnd -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/media/radio/radio-cadet.c b/drivers/media/radio/radio-cadet.c index 545c04c..67b5bbf 100644 --- a/drivers/media/radio/radio-cadet.c +++ b/drivers/media/radio/radio-cadet.c @@ -39,6 +39,7 @@ #include <linux/pnp.h> #include <linux/sched.h> #include <linux/io.h> /* outb, outb_p */ +#include <linux/wait.h> #include <media/v4l2-device.h> #include <media/v4l2-ioctl.h> #include <media/v4l2-ctrls.h> @@ -323,25 +324,32 @@ static ssize_t cadet_read(struct file *file, char __user *data, size_t count, lo struct cadet *dev = video_drvdata(file); unsigned char readbuf[RDS_BUFFER]; int i = 0; + DEFINE_WAIT(wait); mutex_lock(&dev->lock); if (dev->rdsstat == 0) cadet_start_rds(dev); - if (dev->rdsin == dev->rdsout) { + while (1) { + prepare_to_wait(&dev->read_queue, &wait, TASK_INTERRUPTIBLE); + if (dev->rdsin != dev->rdsout) + break; + if (file->f_flags & O_NONBLOCK) { i = -EWOULDBLOCK; goto unlock; } mutex_unlock(&dev->lock); - interruptible_sleep_on(&dev->read_queue); + schedule(); mutex_lock(&dev->lock); } + while (i < count && dev->rdsin != dev->rdsout) readbuf[i++] = dev->rdsbuf[dev->rdsout++]; if (i && copy_to_user(data, readbuf, i)) i = -EFAULT; unlock: + finish_wait(&dev->read_queue, &wait); mutex_unlock(&dev->lock); return i; }
interruptible_sleep_on is racy and going away. This replaces one use in the radio-cadet driver with an open-coded wait loop that lets us check the condition under the mutex but sleep without it. Signed-off-by: Arnd Bergmann <arnd@arndb.de> Cc: Hans Verkuil <hverkuil@xs4all.nl> Cc: Mauro Carvalho Chehab <m.chehab@samsung.com> Cc: linux-media@vger.kernel.org --- drivers/media/radio/radio-cadet.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)