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

From: Peter Zijlstra
Date: Thu Apr 09 2015 - 14:29:00 EST

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().
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