linux-kernel - Re: kdevtmpfs oops since yesterdays vfs merge

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Message-ID: <20110725045851.GA11267@redhat.com>
Date:	Mon, 25 Jul 2011 00:58:52 -0400
From:	Dave Jones <davej@...hat.com>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: kdevtmpfs oops since yesterdays vfs merge

On Mon, Jul 25, 2011 at 03:44:44AM +0100, Al Viro wrote:

 > > when it triggers the bug_on(), it's that second nodename that is garbage.
 > 
 > Interesting...  The next experiment would be to stick BUG_ON(!req.dev)
 > into devtmpfs_create_node() right after the assigment to that field.

couldn't get that to trigger.

 > We couldn't be hit by the lack of barriers here, could we?  Store to
 > req.dev happens before spin_unlock(&req_lock), so by the time when
 > that request is seen by loop in devtmpfsd() and passed to handle() it
 > should be seen - we have grabbed req_lock, found a pointer to req, dropped
 > req_lock and called handle().  Should've been enough...
 > 
 > Might be interesting to print &req from devtmpfs_create_node(), both on
 > entry and on exit, and print req right before the call of handle()...

Here's latest..

https://s3.amazonaws.com/twitpic/photos/full/355219312.jpg?AWSAccessKeyId=AKIAJF3XCCKACR3QDMOA&Expires=1311570683&Signature=xr3tusulMiV2bIsxux9YNrawUDA%3D
 
apologies for crappy picture, but it's legible at fullsize..

interesting thing here is that the req that causes the oops, I couldn't
find any call to create_handle for that address, so where devtmpfsd got it
is a mystery.  The address is curious too, in that it's way off from all the
reqs created around that time.

I'll add some more printk's to see if I can figure where that's being created.

	Dave

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