From: "J. Bruce Fields" <bfields@fieldses.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [git pull] vfs and fs fixes
Date: Tue, 17 Apr 2012 20:47:06 -0400 [thread overview]
Message-ID: <20120418004706.GA1924@fieldses.org> (raw)
In-Reply-To: <CA+55aFwdh_QWG-R2FQ71kDXiNYZ04qPANBsY_PssVUwEBH4uSw@mail.gmail.com>
On Tue, Apr 17, 2012 at 03:08:26PM -0700, Linus Torvalds wrote:
> On Tue, Apr 17, 2012 at 2:14 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> > On Tue, Apr 17, 2012 at 07:28:26PM +0100, Al Viro wrote:>
> > Maybe instead I could continue using the i_mutex but handle rename some
> > other way; e.g. in delegation code:
> >
> > if (!mutex_trylock(inode->i_mutex))
> > return -EAGAIN;
> > if (atomic_read(inode->i_renames_in_progress))
> > return -EAGAIN;
> >
> > and add an
> >
> > atomic_inc(inode->i_renames_in_progress);
> > atomic_dec(inode->i_renames_in_progress);
> >
> > pair around rename.
>
> Please don't make up your own locking. Plus it's broken anyway, since
> a rename could come in directly after your atomic_read (and this is
> *why* people shouldn't make up their own locks - they are invariably
> broken).
Doh, yes, sounds like a good rule. (I was misremembering some previous
attempt at this--which admittedly may just have failed in some more
complicated way.)
--b.
> > Or I could increment that counter for all the conflicting operations and
> > rely on it instead of the i_mutex. I was trying to avoid adding
> > something like that (an inc, a dec, another error path) to every
> > operation. And hoping to avoid adding another field to struct inode.
> > Oh well.
>
> We could just say that we can do a double inode lock, but then
> standardize on the order. And the only sane order is comparing inode
> pointers, not inode numbers like ext4 apparently does.
>
> With a standard order, I don't think it would be at all wrong to just
> take the inode lock on rename.
>
> Linus
next prev parent reply other threads:[~2012-04-18 0:47 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-17 5:25 [git pull] vfs and fs fixes Al Viro
2012-04-17 15:01 ` Linus Torvalds
2012-04-17 16:22 ` J. Bruce Fields
2012-04-17 16:33 ` Linus Torvalds
2012-04-17 17:06 ` J. Bruce Fields
2012-04-17 17:59 ` Al Viro
2012-04-17 18:01 ` Al Viro
2012-04-17 18:28 ` Al Viro
2012-04-17 21:14 ` J. Bruce Fields
2012-04-17 22:08 ` Linus Torvalds
2012-04-17 23:44 ` Al Viro
2012-04-18 0:49 ` J. Bruce Fields
2012-04-18 0:56 ` Linus Torvalds
2012-04-18 21:52 ` J. Bruce Fields
2012-04-25 15:20 ` J. Bruce Fields
2012-04-25 15:22 ` [PATCH 1/5] vfs: fix outdated i_mutex_lock_class documentation bfields
2012-04-25 15:22 ` [PATCH 2/5] vfs: pull ext4's double-i_mutex-locking into common code bfields
2012-04-25 15:22 ` [PATCH 3/5] vfs: don't use PARENT/CHILD lock classes for non-directories bfields
2012-04-25 15:22 ` [PATCH 4/5] vfs: take i_mutex on renamed file bfields
2012-04-25 15:22 ` [PATCH 5/5] vfs: change nondirectory i_mutex ordering to fix quota deadlock bfields
2012-04-25 15:28 ` J. Bruce Fields
2012-04-25 19:53 ` Jan Kara
2012-04-25 19:58 ` J. Bruce Fields
2012-04-20 11:15 ` [git pull] vfs and fs fixes Jan Kara
2012-04-24 19:52 ` J. Bruce Fields
2012-04-24 22:23 ` Jan Kara
2012-04-25 11:29 ` J. Bruce Fields
2012-04-25 16:26 ` Jan Kara
2012-04-25 16:47 ` Steven Whitehouse
2012-04-25 17:11 ` J. Bruce Fields
2012-04-18 0:47 ` J. Bruce Fields [this message]
2012-04-19 3:23 ` Benjamin Herrenschmidt
2012-04-19 14:50 ` Ted Ts'o
2012-04-24 17:40 ` Greg KH
2012-04-24 17:45 ` Al Viro
2012-04-24 17:59 ` Greg KH
2012-04-24 18:04 ` Al Viro
2012-04-24 20:37 ` Greg KH
2013-09-18 22:52 Al Viro
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