linux-kernel - Re: processes hung after sys_renameat, and 'missing' processes

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Date:	Wed, 6 Jun 2012 20:29:14 -0400
From:	Dave Jones <davej@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: processes hung after sys_renameat, and 'missing' processes

On Thu, Jun 07, 2012 at 12:54:04AM +0100, Al Viro wrote:

 > What we need is ->i_mutex on parents.  And I'm much more concerned about
 > this: 7732a557b1342c6e6966efb5f07effcf99f56167 and
 >  3f50fff4dace23d3cfeb195d5cd4ee813cee68b7.
 > 
 > Dave, you seem to be able to reproduce it; could you try with those two
 > commits reverted?  This stuff is *definitely* wrong with the way it
 > treats d_move(); there we might get it with parents not locked at all.
 > 
 > FWIW, I'd suggest adding a check into d_move(); new parent must be
 > locked in all cases and old one whenever dentry has one (i.e. isn't
 > disconnected).  If you can find a violation of that, you very likely
 > have found the cause of that bug.

Like this ?

 void d_move(struct dentry *dentry, struct dentry *target)
 {
        write_seqlock(&rename_lock);
+
+       BUG_ON(!spin_is_locked(&target->d_parent->d_lock));
+
+       if (dentry->d_parent != NULL)
+               BUG_ON(!spin_is_locked(&dentry->d_parent->d_lock));
+
        __d_move(dentry, target);
        write_sequnlock(&rename_lock);
 }


To be clear, do you want me to try that with or without the reverts ?

	Dave

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