linux-kernel - Re: Linux 3.15 .. and continuation of merge window

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Date:	Wed, 11 Jun 2014 18:32:58 +0900
From:	"J. R. Okajima" <hooanon05g@...il.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux 3.15 .. and continuation of merge window


Al Viro:
> So I suspect that the right fix is a bit trickier - in addition to check
> on the fast path (i.e. when trylock gets us the lock on parent), we need
> to
> 	* get rcu_read_lock() before dropping ->d_lock.
> 	* check if dentry is already doomed right after taking rcu_read_lock();
> if not, any value we might see in ->d_parent afterwards will point to object
> not freed until we drop rcu_read_lock.
>
> IOW, something like the delta below.  Comments?

I will try testing later.
For now, as a comment before testing, the patch looks weird for me. It
checks d_lockref.count twice during d_lockref.lock held. It must be the
same result, isn't it? Or does it mean that denty can be handled by
lockref_mark_dead() even if d_lockref.lock is held?


J. R. Okajima
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