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

From: Guenter Roeck <[email-masked]>
Date: Wed, 21 Jan 2015 13:38:59 -0800

On Wed, Jan 21, 2015 at 09:28:33PM +0000, Al Viro wrote:
> On Wed, Jan 21, 2015 at 01:03:20PM -0800, Guenter Roeck wrote:
> > 
> > failing case:
> > 
> > path_lookupat: calling path_init 'usr' flags=40
> > path_init: link_path_walk() returned 0
> > path_lookupat: path_init 'usr' flags=40[50] returned 0
> > walk_component: lookup_fast() returned 1
> > walk_component: lookup_slow() returned 0
> > walk_component: inode=  (null), negative=1
> > do_path_lookup(usr, 0x10)
> > path_lookupat: calling path_init 'usr' flags=50
> > path_init: link_path_walk() returned 0
> > path_lookupat: path_init 'usr' flags=50[50] returned 0
> > mkdir[c74012a0,/kkk] => 0						<==== SIC!
> 
> Cute. 'k' being 0x6b, aka POISON_FREE...  OK, the next question is what's
> been freed under us - I don't believe that it's dentry itself...
> Oh, fuck.  OK, I see what happens.  Look at kern_path_create(); it does
> LOOKUP_PARENT walk, leaving nd->last pointing to the last component of
> the *COPY* of the name it's just created, walked and freed.
> 
Cool.

> OK...  Fortunately, struct nameidata is completely opaque outside of fs/namei.c,
> so we only need to care about a couple of codepaths.
> 
> Folks, could you check if the following on top of linux-next fixes the problem?
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 323957f..cda89c3 100644

Yes, this patch fixes the problem for me.

Guenter