From: "Tobin C. Harding" <me@tobin.cc>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jonathan Corbet <corbet@lwn.net>,
"Tobin C. Harding" <tobin@kernel.org>,
Mauro Carvalho Chehab <mchehab@s-opensource.com>,
Neil Brown <neilb@suse.com>, Randy Dunlap <rdunlap@infradead.org>,
linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 00/24] Convert vfs.txt to vfs.rst
Date: Wed, 3 Apr 2019 06:25:20 +1100 [thread overview]
Message-ID: <20190402192520.GA6285@eros.localdomain> (raw)
In-Reply-To: <20190402164824.GK2217@ZenIV.linux.org.uk>
On Tue, Apr 02, 2019 at 05:48:24PM +0100, Al Viro wrote:
> On Tue, Apr 02, 2019 at 09:49:34AM -0600, Jonathan Corbet wrote:
> > On Wed, 27 Mar 2019 16:16:53 +1100
> > "Tobin C. Harding" <tobin@kernel.org> wrote:
> >
> > > Hi Al,
> > >
> > > This series converts the VFS file Documentation/filesystems/vfs.txt to
> > > reStructuredText format. Please consider taking this series through
> > > your tree as apposed to Jon's tree because this set makes a fair amount
> > > of changes to VFS files (and also the VFS tree and docs tree are out of
> > > sync right now with the recent work by Mauro and Neil).
> >
> > Al, do you have any thoughts on how you want to handle this? I was about
> > to apply Jeff Layton's vfs.txt update, but would rather not create
> > conflicts unnecessarily. Let me know if you'd like me to pick this work
> > up.
>
> Frankly, I would rather see that file be eventually replaced by something
> saner, and I'm not talking about the format.
Are you able to extrapolate on this comment please? Is this something
someone new to the VFS (me) can do with a little nudge in the right
direction or is this something that needs thorough knowledge of the VFS?
> Re Jeff's patch...
>
> + d_prune: called prior to pruning (i.e. unhashing and killing) a hashed
> + dentry from the dcache.
>
> is flat-out misguiding. First of all, it *is* called for unhashed dentries,
> TYVM. Furthermore, "prior to" is far too vague.
This patch includes documentation for d_prune() very similar to Jeff's
patch (taken from a comment somewhere in filesystems code IIRC). I can
have a go at working all the comments below into better documentation if
that is useful (dependant on answer to question above).
thanks,
Tobin.
(leaving text below for reference)
> What really happens: there's a point in state diagram for dentries where
> we commit to destroying a dentry and start taking it apart. That transition
> happens with ->d_lock of dentry, ->i_lock of its inode (if any) and
> ->d_lock of the parent (again, if any) held; ->d_prune() is the last
> chance for filesystem to see the (now doomed) dentry still intact.
>
> It doesn't matter whether it's hashed or not, etc. The locks held
> are sufficient to stabilize pretty much everything[1] in dentry and
> nothing is destroyed yet. The only apparent exception is ->d_count,
> but that's not real - we are guaranteed that there had been no other
> counted references to dentry at the decision point and that none
> could've been added. So this "oh, it's not 0 now, it's gone negative
> after lockref_mark_dead() the caller has just done" is a red herring.
>
> ->d_prune() must not drop/regain any of the locks held by caller.
> It must _not_ free anything attached to dentry - that belongs
> later in the shutdown sequence. If anything, I'm tempted to
> make it take const struct dentry * as argument, just to make
> that clear.
>
> No new (counted) references can be acquired by that point;
> lockless dcache lookup might find our dentry a match, but
> result of such lookup is not going to be legitimized - it's
> doomed to be thrown out as stale.
>
> It really makes more sense as part of struct dentry lifecycle
> description...
>
> [1] in theory, ->d_time might be changed by overlapping lockless
> call of ->d_revalidate(). Up to filesystem - VFS doesn't touch
> that field (and AFAICS only NFS uses it these days).
next prev parent reply other threads:[~2019-04-02 19:25 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-27 5:16 [PATCH v3 00/24] Convert vfs.txt to vfs.rst Tobin C. Harding
2019-03-27 5:16 ` [PATCH v3 01/24] vfs: Remove trailing whitespace Tobin C. Harding
2019-03-27 5:16 ` [PATCH v3 02/24] vfs: Clean up VFS data structure declarations Tobin C. Harding
2019-03-27 5:16 ` [PATCH v3 03/24] fs: Update function docstring for dio_complete() Tobin C. Harding
2019-03-27 5:16 ` [PATCH v3 04/24] fs: Add docstrings to exported functions Tobin C. Harding
2019-03-27 5:16 ` [PATCH v3 05/24] fs: Guard unusual text with backticks Tobin C. Harding
2019-03-27 5:16 ` [PATCH v3 06/24] fs: Update function docstring for simple_write_end() Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 07/24] fs: Fix function docstring for posix_acl_update_mode() Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 08/24] dcache: Remove trailing whitespace Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 09/24] dcache: Fix i.e. usage in coments Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 10/24] dcache: Fix e.g. usage in comment Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 11/24] dcache: Fix docstring comment for d_drop() Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 12/24] dcache: Fix non-docstring comments Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 13/24] dcache: Clean up function docstrings Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 14/24] dcache: Clean up function docstring members Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 15/24] docs: filesystems: vfs: Remove space before tab Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 16/24] docs: filesystems: vfs: Use uniform space after period Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 17/24] docs: filesystems: vfs: Use 72 character column width Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 18/24] docs: filesystems: vfs: Use uniform spacing around headings Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 19/24] docs: filesystems: vfs: Use correct initial heading Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 20/24] docs: filesystems: vfs: Use SPDX identifier Tobin C. Harding
2019-04-01 5:43 ` Mukesh Ojha
2019-03-27 5:17 ` [PATCH v3 21/24] docs: filesystems: vfs: Fix pre-amble indentation Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 22/24] fs: Copy documentation to struct declarations Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 23/24] dcache: Copy documentation to struct declaration Tobin C. Harding
2019-03-27 5:17 ` [PATCH v3 24/24] docs: Convert vfs.txt to reStructuredText format Tobin C. Harding
2019-03-27 5:24 ` [PATCH v3 00/24] Convert vfs.txt to vfs.rst Joe Perches
2019-03-27 6:26 ` Tobin C. Harding
2019-04-02 15:49 ` Jonathan Corbet
2019-04-02 16:48 ` Al Viro
2019-04-02 17:54 ` Al Viro
2019-04-02 19:08 ` Al Viro
2019-04-02 23:36 ` Ian Kent
2019-04-02 23:56 ` Ian Kent
2019-04-03 0:55 ` NeilBrown
2019-04-03 19:35 ` Al Viro
2019-04-04 6:30 ` Ian Kent
2019-04-03 23:28 ` Ian Kent
2019-04-02 19:25 ` Tobin C. Harding [this message]
2019-04-03 19:47 ` Al Viro
2019-04-03 20:59 ` Tobin C. Harding
2019-04-03 1:00 ` NeilBrown
2019-04-03 1:44 ` Al Viro
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