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SubjectRe: [PATCH 03/11] locking, rwsem: introduce basis for down_write_killable
On Wed 11-05-16 11:41:28, Peter Zijlstra wrote:
> On Wed, May 11, 2016 at 11:31:27AM +0200, Michal Hocko wrote:
>
> > Care to cook up a full patch?
>
> compile tested only, if someone could please test it?

I have tried to run the test case from Tetsuo[1] with a small printk to
show the interrupted writer case:
[ 2753.596678] XXX: Writer interrupted. Woken waiters:0
[ 2998.266978] XXX: Writer interrupted. Woken waiters:0

which means rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem) path which is
the problematic case. oom_reaper was always able to succeed so I guess
the patch works as expected. I will leave the test run for longer to be
sure.

[1] http://lkml.kernel.org/r/201605061958.HHG48967.JVFtSLFQOFOOMH@I-love.SAKURA.ne.jp
>
> I'll go write a Changelog if it turns out to actually work ;-)
>
> ---
> kernel/locking/rwsem-xadd.c | 21 +++++++++++++++------
> 1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
> index df4dcb883b50..09e30c6225e5 100644
> --- a/kernel/locking/rwsem-xadd.c
> +++ b/kernel/locking/rwsem-xadd.c
> @@ -487,23 +487,32 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
>
> /* Block until there are no active lockers. */
> do {
> - if (signal_pending_state(state, current)) {
> - raw_spin_lock_irq(&sem->wait_lock);
> - ret = ERR_PTR(-EINTR);
> - goto out;
> - }
> + if (signal_pending_state(state, current))
> + goto out_nolock;
> +
> schedule();
> set_current_state(state);
> } while ((count = sem->count) & RWSEM_ACTIVE_MASK);
>
> raw_spin_lock_irq(&sem->wait_lock);
> }
> -out:
> __set_current_state(TASK_RUNNING);
> list_del(&waiter.list);
> raw_spin_unlock_irq(&sem->wait_lock);
>
> return ret;
> +
> +out_nolock:
> + __set_current_state(TASK_RUNNING);
> + raw_spin_lock_irq(&sem->wait_lock);
> + list_del(&waiter.list);
> + if (list_empty(&sem->wait_list))
> + rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem);
> + else
> + __rwsem_do_wake(sem, RWSEM_WAKE_ANY);
> + raw_spin_unlock_irq(&sem->wait_lock);
> +
> + return ERR_PTR(-EINTR);
> }
>
> __visible struct rw_semaphore * __sched

--
Michal Hocko
SUSE Labs

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