From: "NeilBrown" <neilb@suse.de>
To: "Al Viro" <viro@zeniv.linux.org.uk>
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>,
"Daire Byrne" <daire@dneg.com>,
"Trond Myklebust" <trond.myklebust@hammerspace.com>,
"Chuck Lever" <chuck.lever@oracle.com>,
"Linux NFS Mailing List" <linux-nfs@vger.kernel.org>,
linux-fsdevel@vger.kernel.org,
"LKML" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 01/10] VFS: support parallel updates in the one directory.
Date: Mon, 05 Sep 2022 09:33:40 +1000 [thread overview]
Message-ID: <166233442086.1168.1631109347260612253@noble.neil.brown.name> (raw)
In-Reply-To: <YxOUUEXAbUdFLVKk@ZenIV>
On Sun, 04 Sep 2022, Al Viro wrote:
> On Sat, Sep 03, 2022 at 03:12:26AM +0100, Al Viro wrote:
>
> > Very much so. You are starting to invent new rules for ->lookup() that
> > just never had been there, basing on nothing better than a couple of
> > examples. They are nowhere near everything there is.
>
> A few examples besides NFS and autofs:
Hi Al,
thanks for these - very helpful. I will give them due consideration
when I write relevant documentation to include in the next posting of
the series.
Thanks a lot,
NeilBrown
>
> ext4, f2fs and xfs might bloody well return NULL without hashing - happens
> on negative lookups with 'casefolding' crap.
>
> kernfs - treatment of inactive nodes.
>
> afs_dynroot_lookup() treatment of @cell... names.
>
> afs_lookup() treatment of @sys... names.
>
> There might very well be more - both merged into mainline and in
> development trees of various filesystems (including devel branches
> of in-tree ones - I'm not talking about out-of-tree projects).
>
> Note, BTW, that with the current rules it's perfectly possible to
> have this kind of fun:
> a name that resolves to different files for different processes
> unlink(2) is allowed and results depend upon the calling process
>
> All it takes is ->lookup() deliberately *NOT* hashing the sucker and
> ->unlink() acting according to dentry it has gotten from the caller.
> unlink(2) from different callers are serialized and none of that
> stuff is ever going to be hashed. d_alloc_parallel() might pick an
> in-lookup dentry from another caller of e.g. stat(2), but it will
> wait for in-lookup state ending, notice that the sucker is not hashed,
> drop it and retry. Suboptimal, but it works.
>
> Nothing in the mainline currently does that. Nothing that I know of,
> that is. Sure, it could be made work with the changes you seem to
> imply (if I'm not misreading you) - all it takes is lookup
> calling d_lookup_done() on its argument before returning NULL.
> But that's subtle, non-obvious and not documented anywhere...
>
> Another interesting question is the rules for unhashing dentries.
> What is needed for somebody to do temporary unhash, followed by
> rehashing?
>
next prev parent reply other threads:[~2022-09-04 23:33 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-26 2:10 [PATCH/RFC 00/10 v5] Improve scalability of directory operations NeilBrown
2022-08-26 2:10 ` [PATCH 09/10] VFS: add LOOKUP_SILLY_RENAME NeilBrown
2022-08-27 1:21 ` Al Viro
2022-08-29 3:15 ` NeilBrown
2022-08-26 2:10 ` [PATCH 01/10] VFS: support parallel updates in the one directory NeilBrown
2022-08-26 19:06 ` Linus Torvalds
2022-08-26 23:06 ` NeilBrown
2022-08-27 0:13 ` Linus Torvalds
2022-08-27 0:23 ` Al Viro
2022-08-27 21:14 ` Al Viro
2022-08-27 0:17 ` Al Viro
2022-09-01 0:31 ` NeilBrown
2022-09-01 3:44 ` Al Viro
2022-08-27 3:43 ` Al Viro
2022-08-29 1:59 ` NeilBrown
2022-09-03 0:06 ` Al Viro
2022-09-03 1:40 ` NeilBrown
2022-09-03 2:12 ` Al Viro
2022-09-03 17:52 ` Al Viro
2022-09-04 23:33 ` NeilBrown [this message]
2022-08-26 2:10 ` [PATCH 08/10] NFSD: allow parallel creates from nfsd NeilBrown
2022-08-27 4:37 ` Al Viro
2022-08-29 3:12 ` NeilBrown
2022-08-26 2:10 ` [PATCH 05/10] VFS: export done_path_update() NeilBrown
2022-08-26 2:10 ` [PATCH 02/10] VFS: move EEXIST and ENOENT tests into lookup_hash_update() NeilBrown
2022-08-26 2:10 ` [PATCH 06/10] VFS: support concurrent renames NeilBrown
2022-08-27 4:12 ` Al Viro
2022-08-29 3:08 ` NeilBrown
2022-08-26 2:10 ` [PATCH 10/10] NFS: support parallel updates in the one directory NeilBrown
2022-08-26 15:31 ` John Stoffel
2022-08-26 23:13 ` NeilBrown
2022-08-26 2:10 ` [PATCH 03/10] VFS: move want_write checks into lookup_hash_update() NeilBrown
2022-08-27 3:48 ` Al Viro
2022-08-26 2:10 ` [PATCH 04/10] VFS: move dput() and mnt_drop_write() into done_path_update() NeilBrown
2022-08-26 2:10 ` [PATCH 07/10] VFS: hold DCACHE_PAR_UPDATE lock across d_revalidate() NeilBrown
2022-08-26 14:42 ` [PATCH/RFC 00/10 v5] Improve scalability of directory operations John Stoffel
2022-08-26 23:30 ` NeilBrown
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