From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH 1/2] fs: add support for LOOKUP_NONBLOCK
Date: Fri, 11 Dec 2020 17:29:31 +0000 [thread overview]
Message-ID: <20201211172931.GY3579531@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAHk-=wjkA5Rx+0UjkSFQUqLJK9eRJ_MqoTZ8y2nyt4zXwE9vDg@mail.gmail.com>
On Fri, Dec 11, 2020 at 09:21:20AM -0800, Linus Torvalds wrote:
> On Fri, Dec 11, 2020 at 7:57 AM Jens Axboe <axboe@kernel.dk> wrote:
> >
> > On 12/10/20 7:35 PM, Al Viro wrote:
> > > _IF_ for some theoretical exercise you want to do "lookup without dropping
> > > out of RCU", just add a flag that has unlazy_walk() fail. With -ECHILD.
> > > Strip it away in complete_walk() and have path_init() with that flag
> > > and without LOOKUP_RCU fail with -EAGAIN. All there is to it.
> >
> > Thanks Al, that makes for an easier implementation. I like that suggestion,
> > boils it down to just three hunks (see below).
>
> Ooh. Yes, very nice.
Except for the wrong order in path_init() - the check should go _before_
if (!*s)
flags &= ~LOOKUP_RCU;
for obvious reasons.
Again, that part is trivial - what to do with do_open()/open_last_lookups()
is where the nastiness will be. Basically, it makes sure we bail out in
cases when lookup itself would've blocked, but it does *not* bail out
when equally heavy (and unlikely) blocking sources hit past the complete_walk().
Which makes it rather useless for the caller, unless we get logics added to
that part as well. And _that_ I want to see before we commit to anything.
next prev parent reply other threads:[~2020-12-11 19:15 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-10 20:01 [PATCHSET 0/2] fs: Support for LOOKUP_NONBLOCK / RESOLVE_NONBLOCK Jens Axboe
2020-12-10 20:01 ` [PATCH 1/2] fs: add support for LOOKUP_NONBLOCK Jens Axboe
2020-12-10 20:53 ` Linus Torvalds
2020-12-10 21:06 ` Jens Axboe
2020-12-11 2:45 ` Al Viro
2020-12-11 16:05 ` Jens Axboe
2020-12-11 17:20 ` Al Viro
2020-12-11 17:35 ` Linus Torvalds
2020-12-11 18:50 ` Jens Axboe
2020-12-11 21:51 ` Al Viro
2020-12-11 23:47 ` Jens Axboe
2020-12-11 17:33 ` Matthew Wilcox
2020-12-11 18:55 ` Jens Axboe
2020-12-11 2:35 ` Al Viro
2020-12-11 15:57 ` Jens Axboe
2020-12-11 17:21 ` Linus Torvalds
2020-12-11 17:29 ` Al Viro [this message]
2020-12-11 17:38 ` Al Viro
2020-12-11 17:44 ` Linus Torvalds
2020-12-11 21:46 ` Jens Axboe
2020-12-10 20:01 ` [PATCH 2/2] fs: expose LOOKUP_NONBLOCK through openat2() RESOLVE_NONBLOCK Jens Axboe
2020-12-10 22:29 ` Dave Chinner
2020-12-10 23:12 ` Jens Axboe
2020-12-10 23:29 ` Linus Torvalds
2020-12-11 0:58 ` Dave Chinner
2020-12-11 1:01 ` Linus Torvalds
2020-12-11 3:45 ` Dave Chinner
2020-12-11 18:07 ` Linus Torvalds
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