From: Linus Torvalds <torvalds@linux-foundation.org>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Christoph Hellwig <hch@lst.de>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
John Ogness <john.ogness@linutronix.de>
Subject: Re: [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list())
Date: Fri, 23 Feb 2018 13:35:52 -0800 [thread overview]
Message-ID: <CA+55aFyP9JtyzUzA_S2sdKCK+8CZtNoA3UkXg5X4J0Hf2_ekjg@mail.gmail.com> (raw)
In-Reply-To: <20180223201317.GG30522@ZenIV.linux.org.uk>
On Fri, Feb 23, 2018 at 12:13 PM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> Look:
> dentry placed on a shrink list
> we pick the fucker from the list and lock it.
> we call lock_parent() on it.
> dentry is not a root and it's not deleted, so we proceed.
> trylock fails.
> we grab rcu_read_lock()
> we drop dentry->d_lock
[ deleted the bad things ]
Should we just instead get the ref to the dentry before dropping the
lock, so that nobody else can get to dentry_kill?
This is too subtle, and your fix to check d_lockref.count < 0 sounds
wrong to me. If it's really gone, maybe it has been reused and the
refcount is positive again, but it's something else than a dentry
entirely?
Hmm.
No, you extended the rcu read section, so I guess your patch is fine.
And lock_parent already has that pattern, soiit's not new.
Ok, I agree, looks like lock_parent should just re-check that thing
that it already checked earler, but that now might be true again
because of we dropped d_lock.
Linus
next prev parent reply other threads:[~2018-02-23 21:36 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-22 23:50 [PATCH v2 0/6] fs/dcache: avoid trylock loops John Ogness
2018-02-22 23:50 ` [PATCH v2 1/6] fs/dcache: Remove stale comment from dentry_kill() John Ogness
2018-02-22 23:50 ` [PATCH v2 2/6] fs/dcache: Move dentry_kill() below lock_parent() John Ogness
2018-02-22 23:50 ` [PATCH v2 3/6] fs/dcache: Avoid the try_lock loop in d_delete() John Ogness
2018-02-23 2:08 ` Al Viro
2018-02-22 23:50 ` [PATCH v2 4/6] fs/dcache: Avoid the try_lock loops in dentry_kill() John Ogness
2018-02-23 2:22 ` Al Viro
2018-02-23 3:12 ` Al Viro
2018-02-23 3:16 ` Al Viro
2018-02-23 5:46 ` Al Viro
2018-02-22 23:50 ` [PATCH v2 5/6] fs/dcache: Avoid a try_lock loop in shrink_dentry_list() John Ogness
2018-02-23 3:48 ` Al Viro
2018-02-22 23:50 ` [PATCH v2 6/6] fs/dcache: Avoid remaining " John Ogness
2018-02-23 3:58 ` Al Viro
2018-02-23 4:08 ` Al Viro
2018-02-23 13:57 ` John Ogness
2018-02-23 15:09 ` Al Viro
2018-02-23 17:42 ` Al Viro
2018-02-23 20:13 ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Al Viro
2018-02-23 21:35 ` Linus Torvalds [this message]
2018-02-24 0:22 ` Al Viro
2018-02-25 7:40 ` Al Viro
2018-02-27 5:16 ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) John Ogness
2018-03-12 19:13 ` Al Viro
2018-03-12 20:05 ` Al Viro
2018-03-12 20:33 ` Al Viro
2018-03-13 1:12 ` NeilBrown
2018-04-28 0:10 ` Al Viro
2018-03-12 20:23 ` Eric W. Biederman
2018-03-12 20:39 ` Al Viro
2018-03-12 23:28 ` Eric W. Biederman
2018-03-12 23:52 ` Eric W. Biederman
2018-03-13 0:37 ` Al Viro
2018-03-13 0:50 ` Al Viro
2018-03-13 4:02 ` Eric W. Biederman
2018-03-14 23:20 ` [PATCH] fs: Teach path_connected to handle nfs filesystems with multiple roots Eric W. Biederman
2018-03-15 22:34 ` Al Viro
2018-03-13 0:36 ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) Al Viro
2018-03-12 22:14 ` Thomas Gleixner
2018-03-13 20:46 ` John Ogness
2018-03-13 21:05 ` John Ogness
2018-03-13 23:59 ` Al Viro
2018-03-14 2:58 ` Matthew Wilcox
2018-03-14 8:18 ` John Ogness
2018-03-02 9:04 ` [BUG] lock_parent() breakage when used from shrink_dentry_list() (was Re: [PATCH v2 6/6] fs/dcache: Avoid remaining try_lock loop in shrink_dentry_list()) Sebastian Andrzej Siewior
2018-02-23 0:59 ` [PATCH v2 0/6] fs/dcache: avoid trylock loops Linus Torvalds
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