linux-kernel - Re: [PATCH] autofs4: Use wait_event

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Message-ID: <20180319193031.GC6739@bombadil.infradead.org>
Date:   Mon, 19 Mar 2018 12:30:31 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Ian Kent <raven@...maw.net>, autofs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matthew Wilcox <mawilcox@...rosoft.com>
Subject: Re: [PATCH] autofs4: Use wait_event_killable

On Mon, Mar 19, 2018 at 12:25:58PM -0700, David Rientjes wrote:
> On Mon, 19 Mar 2018, Matthew Wilcox wrote:
> >  	 * wq->name.name is NULL iff the lock is already released
> >  	 * or the mount has been made catatonic.
> >  	 */
> > -	if (wq->name.name) {
> > -		/* Block all but "shutdown" signals while waiting */
> > -		unsigned long shutdown_sigs_mask;
> > -		unsigned long irqflags;
> > -		sigset_t oldset;
> > -
[...]
> > -
> > -		wait_event_interruptible(wq->queue, wq->name.name == NULL);
[...]
> > -	} else {
> > -		pr_debug("skipped sleeping\n");
> > -	}
> > -
> > +	wait_event_killable(wq->queue, wq->name.name == NULL);
>
> I understand converting the wait_event_interruptible() to 
> wait_event_killable(), but why was the above wait_event_interruptible() 
> only called when wq->name.name != NULL?  

My guess is that it was to avoid the overhead of diddling the signal set
when wq->name.name was already NULL.  I don't really kow though, it
predates git history and I'm too lazy to go and poke through the historical
repos to see if that reason was captured by BitKeeper.

> wait_event_{killable,interruptible}() will return without sleeping when 
> wq->name.name == NULL, so I suppose it has something to do with the 
> comment above it.