From: John Ogness <john.ogness@linutronix.de>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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>
Subject: dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list())
Date: Tue, 27 Feb 2018 06:16:28 +0100 [thread overview]
Message-ID: <87bmgbnhar.fsf_-_@linutronix.de> (raw)
In-Reply-To: <20180225073950.GI30522@ZenIV.linux.org.uk> (Al Viro's message of "Sun, 25 Feb 2018 07:40:05 +0000")
On 2018-02-25, Al Viro <viro@ZenIV.linux.org.uk> wrote:
> I'll play with cleaning up and reordering tomorrow after I get some
> sleep. In the meanwhile, the current state of that set is at
> git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git #work.dcache
I have one comment on your new dentry_kill()...
> From e77db95d1ad189c76bcda7b90ac2225e98d776a2 Mon Sep 17 00:00:00 2001
> From: Al Viro <viro@zeniv.linux.org.uk>
> Date: Fri, 23 Feb 2018 21:25:42 -0500
> Subject: [PATCH] get rid of trylock loop around dentry_kill()
>
> In case when trylock in there fails, deal with it directly in
> dentry_kill(). Note that in cases when we drop and retake
> ->d_lock, we need to recheck whether to retain the dentry.
> Another thing is that dropping/retaking ->d_lock might have
> ended up with negative dentry turning into positive; that,
> of course, can happen only once...
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> fs/dcache.c | 34 +++++++++++++++++++++++++++-------
> 1 file changed, 27 insertions(+), 7 deletions(-)
>
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 449c1a5..c1f082d 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -657,23 +657,43 @@ static struct dentry *dentry_kill(struct dentry *dentry)
> struct dentry *parent = NULL;
>
> if (inode && unlikely(!spin_trylock(&inode->i_lock)))
> - goto failed;
> + goto slow_positive;
>
> if (!IS_ROOT(dentry)) {
> parent = dentry->d_parent;
> if (unlikely(!spin_trylock(&parent->d_lock))) {
> - if (inode)
> - spin_unlock(&inode->i_lock);
> - goto failed;
> + parent = __lock_parent(dentry);
> + if (likely(inode || !dentry->d_inode))
> + goto got_locks;
> + /* negative that became positive */
> + if (parent)
> + spin_unlock(&parent->d_lock);
> + inode = dentry->d_inode;
> + goto slow_positive;
> }
> }
> -
> __dentry_kill(dentry);
> return parent;
>
> -failed:
> +slow_positive:
> + spin_unlock(&dentry->d_lock);
> + spin_lock(&inode->i_lock);
> + spin_lock(&dentry->d_lock);
> + parent = lock_parent(dentry);
> +got_locks:
> + if (likely(dentry->d_lockref.count == 1 && !retain_dentry(dentry))) {
> + __dentry_kill(dentry);
> + return parent;
> + }
> + /* we are keeping it, after all */
> + if (inode)
> + spin_unlock(&inode->i_lock);
> + if (parent)
> + spin_unlock(&parent->d_lock);
If someone else has grabbed a reference, it shouldn't be added to the
lru list. Only decremented.
if (entry->d_lockref.count == 1)
> + dentry_lru_add(dentry);
> + dentry->d_lockref.count--;
> spin_unlock(&dentry->d_lock);
> - return dentry; /* try again with same dentry */
> + return NULL;
> }
>
> /*
next prev parent reply other threads:[~2018-02-27 5:16 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
2018-02-24 0:22 ` Al Viro
2018-02-25 7:40 ` Al Viro
2018-02-27 5:16 ` John Ogness [this message]
2018-03-12 19:13 ` dcache: remove trylock loops (was Re: [BUG] lock_parent() breakage when used from shrink_dentry_list()) 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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