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

On Wednesday, January 21, 2015 03:42:16 PM Thierry Reding wrote: > On Wed, Jan 21, 2015 at 12:05:39PM +0100, Sabrina Dubroca wrote: > > 2015-01-21, 04:36:38 +0000, Al Viro wrote: > > > On Tue, Jan 20, 2015 at 08:01:26PM -0800, Guenter Roeck wrote: > > > > With this patch: > > > > > > > > sys_mkdir .:40775 returned -17 > > > > sys_mkdir usr:40775 returned 0 > > > > sys_mkdir usr/lib:40775 returned 0 > > > > sys_mkdir usr/share:40755 returned 0 > > > > sys_mkdir usr/share/udhcpc:40755 returned 0 > > > > sys_mkdir usr/bin:40775 returned 0 > > > > sys_mkdir usr/sbin:40775 returned 0 > > > > sys_mkdir mnt:40775 returned 0 > > > > sys_mkdir proc:40775 returned 0 > > > > sys_mkdir root:40775 returned 0 > > > > sys_mkdir lib:40775 returned 0 > > > > sys_mkdir lib/modules:40775 returned 0 > > > > ... > > > > > > > > and the problem is fixed. > > > > This patch also works for me. > > > > > ... except that it simply confirms that something's fishy with > > > getname_kernel() of ->name of struct filename returned by getname(). > > > IOW, I still do not understand the mechanism of breakage there. > > > > I'm not so sure about that. I tried to copy name to a new string in > > do_path_lookup and that didn't help. > > > > Now, I've removed the > > > > putname(filename); > > > > line from do_path_lookup and I don't get the panic. > > That would indicate that somehow the refcount got unbalanced. Looking > more closely it seems like the various audit_*() function do take a > reference, but maybe that's not enough. I'm thinking the same thing and I think the problem may be that __audit_reusename() is not bumping the filename->refcnt. Can someone who is seeing this problem bump the refcnt in __audit_reusename()? struct filename * __audit_reusename(const __user char *uptr) { struct audit_context *context = current->audit_context; struct audit_names *n; list_for_each_entry(n, &context->names_list, list) { if (!n->name) continue; if (n->name->uptr == uptr) { + n->name->refcnt++; return n->name; } } return NULL; }