linux-kernel - Re: VFS deadlock ?

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Message-ID: <CA+55aFx+O13YuJsZyrTS6O9Kws=1ff-knsSv9rV8wTf8yBrPJg@mail.gmail.com>
Date:	Thu, 21 Mar 2013 15:53:13 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: VFS deadlock ?

On Thu, Mar 21, 2013 at 3:12 PM, Dave Jones <davej@...hat.com> wrote:
>
> it's not just irda fwiw..
>
> p1=rpc p2=rpc p1parent=net p2parent=net

Ok, good. The only rpc/irda that has something in common is
/proc/net/, and they both use proc_mkdir() to create the directory:

    proc_irda = proc_mkdir("irda", init_net.proc_net);
   ...
    sn->proc_net_rpc = proc_mkdir("rpc", net->proc_net);

so it's almost certainly that case. What I do *not* see is how we got
two different dentries for the same name in /proc. But if that
happens, then yes, they will have aliased inodes (because
proc_get_inode() will look them up by "sb,de->low_ino".

Al, any ideas? There shouldn't be some lookup race, because that's
done under the parent inode lock. And multiple mount-points will have
different superblocks, so proc_get_inode() will give them separate
inodes. And bind mounts should have all the same dentry tree. So what
the heck am I missing?

       Linus
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