From: Peter Zijlstra <peterz@infradead.org>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-fsdevel@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>,
Linus Torvalds <torvalds@linux-foundation.org>,
Christoph Hellwig <hch@lst.de>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org,
Paul McKenney <paulmck@linux.vnet.ibm.com>
Subject: Re: [PATCH 3/4] fs/dcache: Avoid the try_lock loop in d_delete()
Date: Fri, 16 Feb 2018 18:30:33 +0100 [thread overview]
Message-ID: <20180216173033.GJ25201@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180216150933.971-4-john.ogness@linutronix.de>
On Fri, Feb 16, 2018 at 04:09:32PM +0100, John Ogness wrote:
>
> inode = dentry->d_inode;
> rcu_read_lock(); <- Protects d_inode from being freed,
> i.e. dentry->d_inode is a valid pointer
> even after dentry->d_lock is dropped
> unlock(dentry->d_lock);
> lock(inode->i_lock);
> lock(dentry->d_lock);
> rcu_read_unlock();
So that is entirely tricky, typically we have to have a lookup _after_
rcu_read_lock().
Here, we rely on not being able to call dentry_free() while we hold
d_lock, which ensure dentry must be valid in the freshly started
rcu-section.
And I suppose that same ensures dentry->d_ionde stays alive. But this
needs a comment at least.
next prev parent reply other threads:[~2018-02-16 17:30 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-16 15:09 [PATCH 0/4] fs/dcache: avoid trylock loops John Ogness
2018-02-16 15:09 ` [PATCH 1/4] fs/dcache: Remove stale comment from dentry_kill() John Ogness
2018-02-16 15:09 ` [PATCH 2/4] fs/dcache: Move dentry_kill() below lock_parent() John Ogness
2018-02-16 15:09 ` [PATCH 3/4] fs/dcache: Avoid the try_lock loop in d_delete() John Ogness
2018-02-16 17:10 ` Peter Zijlstra
2018-02-16 17:30 ` Peter Zijlstra [this message]
2018-02-22 5:18 ` Al Viro
2018-02-22 8:35 ` John Ogness
2018-02-16 15:09 ` [PATCH 4/4] fs/dcache: Avoid the try_lock loops in dentry_kill() John Ogness
2018-02-16 18:03 ` Linus Torvalds
2018-02-16 22:32 ` John Ogness
2018-02-16 22:42 ` Linus Torvalds
2018-02-16 23:05 ` John Ogness
2018-02-16 23:31 ` Linus Torvalds
2018-02-16 23:49 ` John Ogness
2018-02-17 0:06 ` Linus Torvalds
2018-02-19 23:34 ` John Ogness
2018-02-20 0:42 ` Linus Torvalds
2018-02-20 8:39 ` Peter Zijlstra
2018-02-20 8:43 ` Peter Zijlstra
2018-02-22 5:29 ` Al Viro
2018-02-22 5:40 ` Al Viro
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