Subject: Re: linux-next: Tree for Jan 20 -- Kernel panic - Unable to mount root fs

From: Sabrina Dubroca <[email-masked]>
Date: Wed, 21 Jan 2015 00:27:26 +0100

2015-01-20, 23:17:25 +0000, Al Viro wrote:
> 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?

I get

stat("/dev/root") -> -2
stat("dev") -> -2
with the patch applied (+panic)

and:

stat("/dev/root") -> 0
stat("dev") -> 0
with the old version of do_path_lookup.

-- 
Sabrina