Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 09:57:44AM -0400, Waiman Long wrote: > > Afaict the whole .owner=NULL thing in release already stops the spinners > > dead, and the above 'fixes' the debug splat. And this avoids exposing > > that horrible interface and keeps the mucking private to > > rwsem/percpu_rwsem. >

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 09:57:44AM -0400, Waiman Long wrote: > > Afaict the whole .owner=NULL thing in release already stops the spinners > > dead, and the above 'fixes' the debug splat. And this avoids exposing > > that horrible interface and keeps the mucking private to > > rwsem/percpu_rwsem. >

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15/2018 04:51 AM, Peter Zijlstra wrote: > On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: >> The percpu_rwsem_release() is called when the ownership of the embedded >> rwsem is to be transferred to another task. The new owner, however, may >> take a while to get the ownership of

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15/2018 04:51 AM, Peter Zijlstra wrote: > On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: >> The percpu_rwsem_release() is called when the ownership of the embedded >> rwsem is to be transferred to another task. The new owner, however, may >> take a while to get the ownership of

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15/2018 01:42 AM, Amir Goldstein wrote: > On Mon, May 14, 2018 at 10:31 PM, Waiman Long wrote: >> The percpu_rwsem_release() is called when the ownership of the embedded >> rwsem is to be transferred to another task. The new owner, however, may >> take a while to get the

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15/2018 01:42 AM, Amir Goldstein wrote: > On Mon, May 14, 2018 at 10:31 PM, Waiman Long wrote: >> The percpu_rwsem_release() is called when the ownership of the embedded >> rwsem is to be transferred to another task. The new owner, however, may >> take a while to get the ownership of the

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 02:45:32PM +0200, Oleg Nesterov wrote: > On 05/15, Peter Zijlstra wrote: > > > > > > Afaict the whole .owner=NULL thing in release already stops the spinners > > > > > > Not really, the new writer will spin in this case, afaics. > > > > > > But this is another problem and

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 02:45:32PM +0200, Oleg Nesterov wrote: > On 05/15, Peter Zijlstra wrote: > > > > > > Afaict the whole .owner=NULL thing in release already stops the spinners > > > > > > Not really, the new writer will spin in this case, afaics. > > > > > > But this is another problem and

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15, Peter Zijlstra wrote: > > > > Afaict the whole .owner=NULL thing in release already stops the spinners > > > > Not really, the new writer will spin in this case, afaics. > > > > But this is another problem and probably we do not care. The new writer is > > almost impossible in this

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15, Peter Zijlstra wrote: > > > > Afaict the whole .owner=NULL thing in release already stops the spinners > > > > Not really, the new writer will spin in this case, afaics. > > > > But this is another problem and probably we do not care. The new writer is > > almost impossible in this

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 01:06:33PM +0200, Oleg Nesterov wrote: > On 05/15, Peter Zijlstra wrote: > > > > So what's wrong with adding: > > > > if (!read) > > sem->rw_sem.owner = current; > > Agreed, I have already suggested this change twice. Except we obviously > need to check

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 01:06:33PM +0200, Oleg Nesterov wrote: > On 05/15, Peter Zijlstra wrote: > > > > So what's wrong with adding: > > > > if (!read) > > sem->rw_sem.owner = current; > > Agreed, I have already suggested this change twice. Except we obviously > need to check

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15, Jan Kara wrote: > > Now this behavior upsets lockdep and that's why we fool it by telling the > semaphore got released before returning to userspace (through > percpu_rwsem_release() helper) and similarly we tell lockdep we've got the > semaphore when an unfreeze syscall is called by

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15, Jan Kara wrote: > > Now this behavior upsets lockdep and that's why we fool it by telling the > semaphore got released before returning to userspace (through > percpu_rwsem_release() helper) and similarly we tell lockdep we've got the > semaphore when an unfreeze syscall is called by

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15, Peter Zijlstra wrote: > > So what's wrong with adding: > > if (!read) > sem->rw_sem.owner = current; Agreed, I have already suggested this change twice. Except we obviously need to check CONFIG_RWSEM_SPIN_ON_OWNER (->owner doesn't exists otherwise) or even

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On 05/15, Peter Zijlstra wrote: > > So what's wrong with adding: > > if (!read) > sem->rw_sem.owner = current; Agreed, I have already suggested this change twice. Except we obviously need to check CONFIG_RWSEM_SPIN_ON_OWNER (->owner doesn't exists otherwise) or even

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue 15-05-18 10:35:25, Peter Zijlstra wrote: > On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > > The percpu_rwsem_release() is called when the ownership of the embedded > > rwsem is to be transferred to another task. The new owner, however, may > > take a while to get the

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue 15-05-18 10:35:25, Peter Zijlstra wrote: > On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > > The percpu_rwsem_release() is called when the ownership of the embedded > > rwsem is to be transferred to another task. The new owner, however, may > > take a while to get the

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire(). > During that

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire(). > During that

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire(). > During that

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Mon, May 14, 2018 at 03:31:07PM -0400, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire(). > During that

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 8:42 AM, Amir Goldstein wrote: > On Mon, May 14, 2018 at 10:31 PM, Waiman Long wrote: >> The percpu_rwsem_release() is called when the ownership of the embedded >> rwsem is to be transferred to another task. The new owner, however,

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Tue, May 15, 2018 at 8:42 AM, Amir Goldstein wrote: > On Mon, May 14, 2018 at 10:31 PM, Waiman Long wrote: >> The percpu_rwsem_release() is called when the ownership of the embedded >> rwsem is to be transferred to another task. The new owner, however, may >> take a while to get the ownership

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Mon, May 14, 2018 at 10:31 PM, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire().

Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as non-spinnable in percpu_rwsem_release()

On Mon, May 14, 2018 at 10:31 PM, Waiman Long wrote: > The percpu_rwsem_release() is called when the ownership of the embedded > rwsem is to be transferred to another task. The new owner, however, may > take a while to get the ownership of the lock via percpu_rwsem_acquire(). > During that