Re: [PATCH] exit: Use read lock for do_notify_parent() instead of write lock

[Ingo Molnar]

* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:

> On Thu, Apr 09, 2015 at 08:59:08PM +0300, Kirill Tkhai wrote:
> 
> I've not really read your email yet, however:
> 
> > Also, in the future we may think about new rwlock primitive, which atomically
> > drops write lock and acquires read lock. Something like this for example:
> > 
> > include/asm-generic/qrwlock.h:
> > static inline void queue_reduce_locked_write_to_read(struct qrwlock *lock)
> > {
> > 	smp_mb__before_atomic();
> > 	atomic_add(_QR_BIAS - _QW_LOCKED, &lock->cnts);
> > }
> 
> we actually have that for the rwsems: downgrade_write(). So the
> consistent naming would be: queue_downgrade_write().

and 'downgrade_write_lock()' on the rwlock side.

Thanks,

	Ingo
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