Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread Paul E. McKenney
On Mon, Dec 08, 2014 at 08:30:18PM +0100, David Hildenbrand wrote: > > > active_writer is cleared while holding cpuhp_lock, so this should be safe, > > > right? > > > > You lost me on that one. Don't we get to that piece of code precisely > > because we don't hold any of the CPU-hotplug locks?

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
> > active_writer is cleared while holding cpuhp_lock, so this should be safe, > > right? > > You lost me on that one. Don't we get to that piece of code precisely > because we don't hold any of the CPU-hotplug locks? If so, the > writer might well hold all the locks it needs, and might well

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread Paul E. McKenney
On Mon, Dec 08, 2014 at 07:58:14PM +0100, David Hildenbrand wrote: > > On Mon, Dec 08, 2014 at 07:13:03PM +0100, David Hildenbrand wrote: > > > Commit b2c4623dcd07 ("rcu: More on deadlock between CPU hotplug and > > > expedited > > > grace periods") introduced another problem that can easily be

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
> On Mon, Dec 08, 2014 at 07:13:03PM +0100, David Hildenbrand wrote: > > Commit b2c4623dcd07 ("rcu: More on deadlock between CPU hotplug and > > expedited > > grace periods") introduced another problem that can easily be reproduced by > > starting/stopping cpus in a loop. > > > > E.g.: > > for

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread Paul E. McKenney
On Mon, Dec 08, 2014 at 07:13:03PM +0100, David Hildenbrand wrote: > Commit b2c4623dcd07 ("rcu: More on deadlock between CPU hotplug and expedited > grace periods") introduced another problem that can easily be reproduced by > starting/stopping cpus in a loop. > > E.g.: > for i in `seq 5000`;

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
The title should of course say active_writer ... grml David -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at

[PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
Commit b2c4623dcd07 ("rcu: More on deadlock between CPU hotplug and expedited grace periods") introduced another problem that can easily be reproduced by starting/stopping cpus in a loop. E.g.: for i in `seq 5000`; do echo 1 > /sys/devices/system/cpu/cpu1/online echo 0 >

[PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
Commit b2c4623dcd07 (rcu: More on deadlock between CPU hotplug and expedited grace periods) introduced another problem that can easily be reproduced by starting/stopping cpus in a loop. E.g.: for i in `seq 5000`; do echo 1 /sys/devices/system/cpu/cpu1/online echo 0

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
The title should of course say active_writer ... grml David -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread Paul E. McKenney
On Mon, Dec 08, 2014 at 07:13:03PM +0100, David Hildenbrand wrote: Commit b2c4623dcd07 (rcu: More on deadlock between CPU hotplug and expedited grace periods) introduced another problem that can easily be reproduced by starting/stopping cpus in a loop. E.g.: for i in `seq 5000`; do

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
On Mon, Dec 08, 2014 at 07:13:03PM +0100, David Hildenbrand wrote: Commit b2c4623dcd07 (rcu: More on deadlock between CPU hotplug and expedited grace periods) introduced another problem that can easily be reproduced by starting/stopping cpus in a loop. E.g.: for i in `seq 5000`;

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread Paul E. McKenney
On Mon, Dec 08, 2014 at 07:58:14PM +0100, David Hildenbrand wrote: On Mon, Dec 08, 2014 at 07:13:03PM +0100, David Hildenbrand wrote: Commit b2c4623dcd07 (rcu: More on deadlock between CPU hotplug and expedited grace periods) introduced another problem that can easily be reproduced

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread David Hildenbrand
active_writer is cleared while holding cpuhp_lock, so this should be safe, right? You lost me on that one. Don't we get to that piece of code precisely because we don't hold any of the CPU-hotplug locks? If so, the writer might well hold all the locks it needs, and might well change

Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock

2014-12-08 Thread Paul E. McKenney
On Mon, Dec 08, 2014 at 08:30:18PM +0100, David Hildenbrand wrote: active_writer is cleared while holding cpuhp_lock, so this should be safe, right? You lost me on that one. Don't we get to that piece of code precisely because we don't hold any of the CPU-hotplug locks? If so, the