* [PATCH] gpss: core: no waiters left behind on deregister @ 2019-06-24 8:33 Oliver Neukum 2019-06-25 7:04 ` Johan Hovold 2019-06-25 10:47 ` Sergei Shtylyov 0 siblings, 2 replies; 6+ messages in thread From: Oliver Neukum @ 2019-06-24 8:33 UTC (permalink / raw) To: johan, linux-usb; +Cc: Oliver Neukum If you deregister a device you need to wake up all waiters as there will be no further wakeups. Signed-off-by: Oliver Neukum <oneukum@suse.com> --- drivers/gnss/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c index e6f94501cb28..0d13bd2cefd5 100644 --- a/drivers/gnss/core.c +++ b/drivers/gnss/core.c @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev) down_write(&gdev->rwsem); gdev->disconnected = true; if (gdev->count) { - wake_up_interruptible(&gdev->read_queue); + wake_up_interruptible_all(&gdev->read_queue); gdev->ops->close(gdev); } up_write(&gdev->rwsem); -- 2.16.4 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] gpss: core: no waiters left behind on deregister 2019-06-24 8:33 [PATCH] gpss: core: no waiters left behind on deregister Oliver Neukum @ 2019-06-25 7:04 ` Johan Hovold 2019-06-26 11:04 ` Oliver Neukum 2019-06-25 10:47 ` Sergei Shtylyov 1 sibling, 1 reply; 6+ messages in thread From: Johan Hovold @ 2019-06-25 7:04 UTC (permalink / raw) To: Oliver Neukum; +Cc: johan, linux-usb On Mon, Jun 24, 2019 at 10:33:23AM +0200, Oliver Neukum wrote: > If you deregister a device you need to wake up all waiters > as there will be no further wakeups. > > Signed-off-by: Oliver Neukum <oneukum@suse.com> > --- > drivers/gnss/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c > index e6f94501cb28..0d13bd2cefd5 100644 > --- a/drivers/gnss/core.c > +++ b/drivers/gnss/core.c > @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev) > down_write(&gdev->rwsem); > gdev->disconnected = true; > if (gdev->count) { > - wake_up_interruptible(&gdev->read_queue); > + wake_up_interruptible_all(&gdev->read_queue); GNSS core doesn't have any exclusive waiters, so no need to use use the exclusive wake-up (all) interface. > gdev->ops->close(gdev); > } > up_write(&gdev->rwsem); Thanks, Johan ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] gpss: core: no waiters left behind on deregister 2019-06-25 7:04 ` Johan Hovold @ 2019-06-26 11:04 ` Oliver Neukum 2019-06-26 11:41 ` Johan Hovold 0 siblings, 1 reply; 6+ messages in thread From: Oliver Neukum @ 2019-06-26 11:04 UTC (permalink / raw) To: Johan Hovold; +Cc: linux-usb Am Dienstag, den 25.06.2019, 09:04 +0200 schrieb Johan Hovold: > On Mon, Jun 24, 2019 at 10:33:23AM +0200, Oliver Neukum wrote: > > If you deregister a device you need to wake up all waiters > > as there will be no further wakeups. > > > > Signed-off-by: Oliver Neukum <oneukum@suse.com> > > --- > > drivers/gnss/core.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c > > index e6f94501cb28..0d13bd2cefd5 100644 > > --- a/drivers/gnss/core.c > > +++ b/drivers/gnss/core.c > > @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev) > > down_write(&gdev->rwsem); > > gdev->disconnected = true; > > if (gdev->count) { > > - wake_up_interruptible(&gdev->read_queue); > > + wake_up_interruptible_all(&gdev->read_queue); > > GNSS core doesn't have any exclusive waiters, so no need to use use the > exclusive wake-up (all) interface. Well, yes, but that is the problem. In gnss_read() you drop the lock: mutex_lock(&gdev->read_mutex); while (kfifo_is_empty(&gdev->read_fifo)) { mutex_unlock(&gdev->read_mutex); if (gdev->disconnected) return 0; if (file->f_flags & O_NONBLOCK) return -EAGAIN; That means that an arbitrary number of tasks can get here. ret = wait_event_interruptible(gdev->read_queue, gdev->disconnected || !kfifo_is_empty(&gdev->read_fifo)); Meaning that an arbitrary number can be sleeping here. Yet in gnss_deregister_device() you use a simple wake_up: void gnss_deregister_device(struct gnss_device *gdev) { down_write(&gdev->rwsem); gdev->disconnected = true; if (gdev->count) { wake_up_interruptible(&gdev->read_queue); wake_up_interruptible() will wake up one waiting task. But after that the device is gone. There will be no further events. The other tasks will sleep forever. Regards Oliver ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] gpss: core: no waiters left behind on deregister 2019-06-26 11:04 ` Oliver Neukum @ 2019-06-26 11:41 ` Johan Hovold 2019-07-01 10:00 ` Oliver Neukum 0 siblings, 1 reply; 6+ messages in thread From: Johan Hovold @ 2019-06-26 11:41 UTC (permalink / raw) To: Oliver Neukum; +Cc: Johan Hovold, linux-usb On Wed, Jun 26, 2019 at 01:04:07PM +0200, Oliver Neukum wrote: > Am Dienstag, den 25.06.2019, 09:04 +0200 schrieb Johan Hovold: > > On Mon, Jun 24, 2019 at 10:33:23AM +0200, Oliver Neukum wrote: > > > If you deregister a device you need to wake up all waiters > > > as there will be no further wakeups. > > > > > > Signed-off-by: Oliver Neukum <oneukum@suse.com> > > > --- > > > drivers/gnss/core.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c > > > index e6f94501cb28..0d13bd2cefd5 100644 > > > --- a/drivers/gnss/core.c > > > +++ b/drivers/gnss/core.c > > > @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev) > > > down_write(&gdev->rwsem); > > > gdev->disconnected = true; > > > if (gdev->count) { > > > - wake_up_interruptible(&gdev->read_queue); > > > + wake_up_interruptible_all(&gdev->read_queue); > > > > GNSS core doesn't have any exclusive waiters, so no need to use use the > > exclusive wake-up (all) interface. > > Well, yes, but that is the problem. In gnss_read() you drop the lock: > That means that an arbitrary number of tasks can get here. > > ret = wait_event_interruptible(gdev->read_queue, > gdev->disconnected || > !kfifo_is_empty(&gdev->read_fifo)); > > Meaning that an arbitrary number can be sleeping here. I understand wait you're getting at, but I think your mistaken regarding exclusive wait. Note that wait_event_interruptible() uses nonexclusive wait. > Yet in gnss_deregister_device() you use a simple wake_up: > > void gnss_deregister_device(struct gnss_device *gdev) > > { > > down_write(&gdev->rwsem); > gdev->disconnected = true; > if (gdev->count) { > wake_up_interruptible(&gdev->read_queue); > > > wake_up_interruptible() will wake up one waiting task. But after that > the device is gone. There will be no further events. The other tasks > will sleep forever. No, wake_up_interruptible() will wake up all nonexclusive waiters, which is all we care about here. Johan ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] gpss: core: no waiters left behind on deregister 2019-06-26 11:41 ` Johan Hovold @ 2019-07-01 10:00 ` Oliver Neukum 0 siblings, 0 replies; 6+ messages in thread From: Oliver Neukum @ 2019-07-01 10:00 UTC (permalink / raw) To: Johan Hovold; +Cc: linux-usb Am Mittwoch, den 26.06.2019, 13:41 +0200 schrieb Johan Hovold: > On Wed, Jun 26, 2019 at 01:04:07PM +0200, Oliver Neukum wrote: > > Am Dienstag, den 25.06.2019, 09:04 +0200 schrieb Johan Hovold: > > > On Mon, Jun 24, 2019 at 10:33:23AM +0200, Oliver Neukum wrote: > > > > If you deregister a device you need to wake up all waiters > > > > as there will be no further wakeups. > > > > > > > > Signed-off-by: Oliver Neukum <oneukum@suse.com> > > > > --- > > > > drivers/gnss/core.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c > > > > index e6f94501cb28..0d13bd2cefd5 100644 > > > > --- a/drivers/gnss/core.c > > > > +++ b/drivers/gnss/core.c > > > > @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev) > > > > down_write(&gdev->rwsem); > > > > gdev->disconnected = true; > > > > if (gdev->count) { > > > > - wake_up_interruptible(&gdev->read_queue); > > > > + wake_up_interruptible_all(&gdev->read_queue); > > > > > > GNSS core doesn't have any exclusive waiters, so no need to use use the > > > exclusive wake-up (all) interface. > > > > Well, yes, but that is the problem. In gnss_read() you drop the lock: > > That means that an arbitrary number of tasks can get here. > > > > ret = wait_event_interruptible(gdev->read_queue, > > gdev->disconnected || > > !kfifo_is_empty(&gdev->read_fifo)); > > > > Meaning that an arbitrary number can be sleeping here. > > I understand wait you're getting at, but I think your mistaken regarding > exclusive wait. Note that wait_event_interruptible() uses nonexclusive > wait. > > > Yet in gnss_deregister_device() you use a simple wake_up: > > > > void gnss_deregister_device(struct gnss_device *gdev) > > > > { > > > > down_write(&gdev->rwsem); > > gdev->disconnected = true; > > if (gdev->count) { > > wake_up_interruptible(&gdev->read_queue); > > > > > > wake_up_interruptible() will wake up one waiting task. But after that > > the device is gone. There will be no further events. The other tasks > > will sleep forever. > > No, wake_up_interruptible() will wake up all nonexclusive waiters, > which is all we care about here. You are right and tracing this is hard. Regards & Sorry Oliver ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] gpss: core: no waiters left behind on deregister 2019-06-24 8:33 [PATCH] gpss: core: no waiters left behind on deregister Oliver Neukum 2019-06-25 7:04 ` Johan Hovold @ 2019-06-25 10:47 ` Sergei Shtylyov 1 sibling, 0 replies; 6+ messages in thread From: Sergei Shtylyov @ 2019-06-25 10:47 UTC (permalink / raw) To: Oliver Neukum, johan, linux-usb Hello! The subject has gpss ISO gnss. You hardly meant the General Purpose System Simulation. :-) On 24.06.2019 11:33, Oliver Neukum wrote: > If you deregister a device you need to wake up all waiters > as there will be no further wakeups. > > Signed-off-by: Oliver Neukum <oneukum@suse.com> > --- > drivers/gnss/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gnss/core.c b/drivers/gnss/core.c > index e6f94501cb28..0d13bd2cefd5 100644 > --- a/drivers/gnss/core.c > +++ b/drivers/gnss/core.c > @@ -303,7 +303,7 @@ void gnss_deregister_device(struct gnss_device *gdev) > down_write(&gdev->rwsem); > gdev->disconnected = true; > if (gdev->count) { > - wake_up_interruptible(&gdev->read_queue); > + wake_up_interruptible_all(&gdev->read_queue); > gdev->ops->close(gdev); > } > up_write(&gdev->rwsem); MBR, Sergei ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-07-01 10:14 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-06-24 8:33 [PATCH] gpss: core: no waiters left behind on deregister Oliver Neukum 2019-06-25 7:04 ` Johan Hovold 2019-06-26 11:04 ` Oliver Neukum 2019-06-26 11:41 ` Johan Hovold 2019-07-01 10:00 ` Oliver Neukum 2019-06-25 10:47 ` Sergei Shtylyov
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