From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-ia64@vger.kernel.org,
Linux-sh list <linux-sh@vger.kernel.org>,
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Subject: Re: [PATCH v12 10/12] namei: aggressively check for nd->root escape on ".." resolution
Date: Wed, 4 Sep 2019 16:44:54 -0700 [thread overview]
Message-ID: <CAHk-=wjx3y1Y7iE6T0yiERc8G5iT1sTABWbX_nFxw9NVHCFCPA@mail.gmail.com> (raw)
In-Reply-To: <20190904232911.GN1131@ZenIV.linux.org.uk>
On Wed, Sep 4, 2019 at 4:29 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Wed, Sep 04, 2019 at 03:38:20PM -0700, Linus Torvalds wrote:
> > On Wed, Sep 4, 2019 at 3:31 PM David Howells <dhowells@redhat.com> wrote:
> > >
> > > It ought to be reasonably easy to make them per-sb at least, I think. We
> > > don't allow cross-super rename, right?
> >
> > Right now the sequence count handling very much depends on it being a
> > global entity on the reader side, at least.
> >
> > And while the rename sequence count could (and probably should) be
> > per-sb, the same is very much not true of the mount one.
>
> Huh? That will cost us having to have a per-superblock dentry
> hash table; recall that lockless lockup can give false negatives
> if something gets moved from chain to chain, and rename_lock is
> first and foremost used to catch those and retry. If we split
> it on per-superblock basis, we can't have dentries from different
> superblocks in the same chain anymore...
That's exactly the "very much depends on it being a global entity on
the reader side" thing.
I'm not convinced that's the _only_ way to handle things. Maybe a
combination of (wild handwaving) per-hashqueue sequence count and some
clever scheme for pathname handling could work.
I've not personally seen a load where the global rename lock has been
a problem (very few things really do a lot of renames), but
system-wide locks do make me nervous.
We have other (and worse) ones. tasklist_lock comes to mind.
Linus
next prev parent reply other threads:[~2019-09-04 23:55 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-04 20:19 [PATCH v12 00/12] namei: openat2(2) path resolution restrictions Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Aleksa Sarai
2019-09-04 20:48 ` [PATCH v12 01/12] lib: introduce copy_struct_{to, from}_user helpers Linus Torvalds
2019-09-04 21:00 ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Randy Dunlap
2019-09-05 7:32 ` Peter Zijlstra
2019-09-05 9:26 ` Aleksa Sarai
2019-09-05 9:43 ` Peter Zijlstra
2019-09-05 10:57 ` Peter Zijlstra
2019-09-11 10:37 ` Aleksa Sarai
2019-09-05 13:35 ` Aleksa Sarai
2019-09-05 17:01 ` Aleksa Sarai
2019-09-05 8:43 ` Rasmus Villemoes
2019-09-05 9:50 ` Aleksa Sarai
2019-09-05 10:45 ` Christian Brauner
2019-09-05 9:09 ` [PATCH v12 01/12] lib: introduce copy_struct_{to, from}_user helpers Andreas Schwab
2019-09-05 10:13 ` Gabriel Paubert
2019-09-05 11:05 ` [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Christian Brauner
2019-09-05 11:17 ` Rasmus Villemoes
2019-09-05 11:29 ` Christian Brauner
2019-09-05 13:40 ` Aleksa Sarai
2019-09-05 11:09 ` Christian Brauner
2019-09-05 11:27 ` Aleksa Sarai
2019-09-05 11:40 ` Christian Brauner
2019-09-05 18:07 ` Al Viro
2019-09-05 18:23 ` Christian Brauner
2019-09-05 18:28 ` Al Viro
2019-09-05 18:35 ` Christian Brauner
2019-09-05 19:56 ` Aleksa Sarai
2019-09-05 22:31 ` Al Viro
2019-09-06 7:00 ` Christian Brauner
2019-09-05 23:00 ` Aleksa Sarai
2019-09-05 23:49 ` Al Viro
2019-09-06 0:09 ` Aleksa Sarai
2019-09-06 0:14 ` Al Viro
2019-09-04 20:19 ` [PATCH v12 02/12] clone3: switch to copy_struct_from_user() Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 03/12] sched_setattr: switch to copy_struct_{to, from}_user() Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 04/12] perf_event_open: switch to copy_struct_from_user() Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 05/12] namei: obey trailing magic-link DAC permissions Aleksa Sarai
2019-09-17 21:30 ` Jann Horn
2019-09-18 13:51 ` Aleksa Sarai
2019-09-18 15:46 ` Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 06/12] procfs: switch magic-link modes to be more sane Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 07/12] open: O_EMPTYPATH: procfs-less file descriptor re-opening Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 08/12] namei: O_BENEATH-style path resolution flags Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 09/12] namei: LOOKUP_IN_ROOT: chroot-like path resolution Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 10/12] namei: aggressively check for nd->root escape on ".." resolution Aleksa Sarai
2019-09-04 21:09 ` Linus Torvalds
2019-09-04 21:35 ` Linus Torvalds
2019-09-04 21:36 ` Linus Torvalds
2019-09-04 21:48 ` Aleksa Sarai
2019-09-04 22:16 ` Linus Torvalds
2019-09-04 22:31 ` David Howells
2019-09-04 22:38 ` Linus Torvalds
2019-09-04 23:29 ` Al Viro
2019-09-04 23:44 ` Linus Torvalds [this message]
2019-09-04 20:19 ` [PATCH v12 11/12] open: openat2(2) syscall Aleksa Sarai
2019-09-04 21:00 ` Randy Dunlap
2019-09-07 12:40 ` Jeff Layton
2019-09-07 16:58 ` Linus Torvalds
2019-09-07 17:42 ` Andy Lutomirski
2019-09-07 17:45 ` Linus Torvalds
2019-09-07 18:15 ` Andy Lutomirski
2019-09-10 6:35 ` Ingo Molnar
2019-09-08 16:24 ` Aleksa Sarai
2019-09-04 20:19 ` [PATCH v12 12/12] selftests: add openat2(2) selftests Aleksa Sarai
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