Re: Introduce atomic_dec_and_lock_irqsave()

[Peter Zijlstra]

On Fri, May 04, 2018 at 05:26:40PM +0100, Al Viro wrote:
> On Fri, May 04, 2018 at 06:21:02PM +0200, Peter Zijlstra wrote:
> > On Fri, May 04, 2018 at 06:07:26PM +0200, Sebastian Andrzej Siewior wrote:
> > 
> > > do you intend to kill refcount_dec_and_lock() in the longterm?
> > 
> > You meant to say atomic_dec_and_lock() ? Dunno if we ever get there, but
> > typically dec_and_lock is fairly refcounty, but I suppose it is possible
> > to have !refcount users, in which case we're eternally stuck with it.
> 
> Yes, there are - consider e.g.
> 
> void iput(struct inode *inode)
> { 
>         if (!inode)
>                 return;
>         BUG_ON(inode->i_state & I_CLEAR);
> retry:
>         if (atomic_dec_and_lock(&inode->i_count, &inode->i_lock)) {
> 
> inode->i_count sure as hell isn't refcount_t fodder...

Yeah, I should've remembered, I tried to convert that once ;-) i_count is
a usage count, not a refcount.