linux-kernel - Re: [GIT PULL] killable rwsems for v4.7

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Message-ID: <CA+55aFyf5M+QQi21yJ0VVxf0iSzcPHxWvCgT+TwgVUiY8Fqf9Q@mail.gmail.com>
Date:	Tue, 17 May 2016 11:31:10 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Michal Hocko <mhocko@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] killable rwsems for v4.7

On Tue, May 17, 2016 at 11:05 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> I'm not sure - killable write is needed in a bunch of places there (and the
> only reason it's not used in #work.lookups is to avoid even more merge
> headache; as soon as both are merged, I'll post a trivial followup switching
> half a dozen places to it), killable read...  Do we really need it?
> The only plausible user right now (->i_rwsem one, that is) is parallel readdir.
> And I'm not convinced that we need to make that one killable.  We can
> (down_read_killable seems to be easy to put together), but is it worth
> using it in that usecase?

It may not be a big deal.

Especially since I also expect to merge the "stop readdir in the
middle if a signal is pending" patch that was buggy last time around
but Ted has a fixed and extended version of it.

So together with the fact that most of the time we hopefully end up
not blocking anyway (because taking the rwsem for writing is hopefully
less common) I guess that the possible latency issue just isn't going
to ever be noticeable.

So let's just see if we ever hit a situation where people end up even
noticing the issue.

              Linus