From: Linus Torvalds <torvalds@linux-foundation.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/4] fs/dcache: Avoid the try_lock loops in dentry_kill()
Date: Fri, 16 Feb 2018 14:42:36 -0800 [thread overview]
Message-ID: <CA+55aFxku7bB9BEBrqgREc5ac4MK9CGLir1c7ZA-7bjp-Q2tAg@mail.gmail.com> (raw)
In-Reply-To: <87y3js36s7.fsf@linutronix.de>
On Fri, Feb 16, 2018 at 2:32 PM, John Ogness <john.ogness@linutronix.de> wrote:
>
> lock_parent() already has the problem you are referring to. Callers are
> required to recheck the dentry contents and check the returned parent
> because they do not know if the trylock succeeded. See
> d_prune_aliases(), for example.
What are you talking about?
lock_parent() does the nice "spin_trylock succeeded" special case.
Yes, it will then do the "unlock dentry, do the parent first, then
re-check" too, and callers may need to worry about it.
But that's not what I'm complaining about in your patch. You remove
the simple case, and make dentry_kill() do the "recheck in case I
dropped" every single time.
It's the "turn a simple case into a complex case" that I absolutely detest.
The fact that there are _other_ complex cases doesn't make it any
better. The whole "but Bobby does it too" thing is not a defense.
Would you jump off a bridge just because your friend did it?
Linus
next prev parent reply other threads:[~2018-02-16 22:42 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-16 15:09 [PATCH 0/4] fs/dcache: avoid trylock loops John Ogness
2018-02-16 15:09 ` [PATCH 1/4] fs/dcache: Remove stale comment from dentry_kill() John Ogness
2018-02-16 15:09 ` [PATCH 2/4] fs/dcache: Move dentry_kill() below lock_parent() John Ogness
2018-02-16 15:09 ` [PATCH 3/4] fs/dcache: Avoid the try_lock loop in d_delete() John Ogness
2018-02-16 17:10 ` Peter Zijlstra
2018-02-16 17:30 ` Peter Zijlstra
2018-02-22 5:18 ` Al Viro
2018-02-22 8:35 ` John Ogness
2018-02-16 15:09 ` [PATCH 4/4] fs/dcache: Avoid the try_lock loops in dentry_kill() John Ogness
2018-02-16 18:03 ` Linus Torvalds
2018-02-16 22:32 ` John Ogness
2018-02-16 22:42 ` Linus Torvalds [this message]
2018-02-16 23:05 ` John Ogness
2018-02-16 23:31 ` Linus Torvalds
2018-02-16 23:49 ` John Ogness
2018-02-17 0:06 ` Linus Torvalds
2018-02-19 23:34 ` John Ogness
2018-02-20 0:42 ` Linus Torvalds
2018-02-20 8:39 ` Peter Zijlstra
2018-02-20 8:43 ` Peter Zijlstra
2018-02-22 5:29 ` Al Viro
2018-02-22 5:40 ` Al Viro
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