linux-kernel - Re: linux-next: Tree for Jan 20 -- Kernel panic

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Message-ID: <20150120231725.GL29656@ZenIV.linux.org.uk>
Date:	Tue, 20 Jan 2015 23:17:25 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Sabrina Dubroca <sd@...asysnail.net>,
	Paul Moore <pmoore@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	linux-next@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-audit@...hat.com,
	Richard Guy Briggs <rgb@...hat.com>
Subject: Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount
 root fs

On Tue, Jan 20, 2015 at 10:50:41PM +0000, Al Viro wrote:
> doesn't look at _anything_ other than name->name other than for audit_inode().
> And name->name is apparently the same.
> 
> It looks like something ends up buggering name->name in process, but then
> the damn thing appears to be normal after return from filename_lookup()...

If my reconstruction of what's going on is correct, the call chain here
is do_path_lookup() <- kern_path() <- lookup_bdev() <- blkdev_get_by_path()
<- mount_bdev() <- some_type.mount() <- mount_fs()
<- vfs_kern_mount() <- do_new_mount() <- do_mount() <- sys_mount()
<- do_mount_root() <- mount_block_root() <- mount_root().  Which is
obscenely long, BTW, but that's a separate story...

Could you slap
	struct stat buf;
	int n = sys_newstat(name, &buf);
	printk(KERN_ERR "stat(\"%s\") -> %d\n", name, n);
	n = sys_newstat("/dev", &buf);
	printk(KERN_ERR "stat(\"dev\") -> %d\n", n);

in the beginning of mount_block_root() (init/do_mounts.c) and see what it
prints?
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