Re: [PATCH 1/2] brw_mutex: big read-write mutex

[Mikulas Patocka]

On Fri, 26 Oct 2012, Oleg Nesterov wrote:

> > The code is different, but it can be changed to use percpu rw semaphores
> > (if we add percpu_down_write_trylock).
> 
> I don't really understand how you can make percpu_down_write_trylock()
> atomic so that it can be called under br_write_lock(vfsmount_lock) in
> sb_prepare_remount_readonly(). So I guess you also need to replace
> vfsmount_lock at least. Or _trylock needs the barriers in _down_read.
> Or I missed something.
> 
> Oleg.

That's true - that code is under spinlock and you can't implement 
non-blocking percpu_down_write_trylock.

Mikulas
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