From: Linus Torvalds <torvalds@linux-foundation.org>
To: NeilBrown <neilb@suse.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 3/3] VFS: close race between getcwd() and d_move()
Date: Thu, 9 Nov 2017 12:23:19 -0800 [thread overview]
Message-ID: <CA+55aFxaoyND1DDk5HqUw97i6-+uMRBbCx4mo=yTKYnBnO2owg@mail.gmail.com> (raw)
In-Reply-To: <151019772763.30101.16040338743875884111.stgit@noble>
On Wed, Nov 8, 2017 at 7:22 PM, NeilBrown <neilb@suse.com> wrote:
> d_move() will call __d_drop() and then __d_rehash()
> on the dentry being moved. This creates a small window
> when the dentry appears to be unhashed. Many tests
> of d_unhashed() are made under ->d_lock and so are safe
> from racing with this window, but some aren't.
> In particular, getcwd() calls d_unlinked() (which calls
> d_unhashed()) without d_lock protection, so it can race.
Hmm.
I see what you're doing, but I don't necessarily agree.
I would actually almost prefer that we simply change __d_move() itself.
The problem is that __d_move() really wants to move the hashes things
atomically, but instead of doing that it does a "unhash and then
rehash".
How nasty would it be to just expand the calls to __d_drop/__d_rehash
into __d_move itself, and take both has list locks at the same time
(with the usual ordering and checking if it's the same list, of
course).
Linus
next prev parent reply other threads:[~2017-11-09 20:23 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-09 3:22 [PATCH 0/3] Three VFS patch resends NeilBrown
2017-11-09 3:22 ` [PATCH 1/3] VFS: use synchronize_rcu_expedited() in namespace_unlock() NeilBrown
2017-11-09 3:22 ` [PATCH 2/3] Improve fairness when locking the per-superblock s_anon list NeilBrown
2017-11-09 19:52 ` Linus Torvalds
2017-11-09 20:50 ` Al Viro
2017-11-09 23:09 ` NeilBrown
2017-11-09 23:19 ` Al Viro
2017-11-10 0:02 ` Linus Torvalds
2017-11-10 8:50 ` Christoph Hellwig
2017-11-09 3:22 ` [PATCH 3/3] VFS: close race between getcwd() and d_move() NeilBrown
2017-11-09 11:41 ` Nikolay Borisov
2017-11-09 13:08 ` Matthew Wilcox
2017-11-09 16:02 ` Nikolay Borisov
2017-11-09 20:23 ` Linus Torvalds [this message]
2017-11-09 22:14 ` NeilBrown
2017-11-10 1:40 ` Linus Torvalds
2017-11-10 4:45 ` NeilBrown
2017-11-10 19:52 ` Linus Torvalds
2017-11-10 20:53 ` Al Viro
2017-11-21 23:50 ` Al Viro
2017-11-22 1:31 ` NeilBrown
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