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

On Wed, Jan 21, 2015 at 01:03:20PM -0800, Guenter Roeck wrote: > ok case (putname commented out): > > user_path_at_empty lookup usr flags 0x0 > 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,/usr] => 0 > user_path_at_empty lookup usr flags 0x1 > path_lookupat: calling path_init 'usr' flags=41 > path_init: link_path_walk() returned 0 > path_lookupat: path_init 'usr' flags=41[51] returned 0 > walk_component: inode=c74004a0, negative=0 > user_path_at_empty lookup usr flags 0x1 > path_lookupat: calling path_init 'usr' flags=41 > path_init: link_path_walk() returned 0 > path_lookupat: path_init 'usr' flags=41[51] returned 0 > > 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. 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?