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Date: Wed, 25 May 2016 16:51:31 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Jeff Chua <jeff.chua.linux@gmail.com>
Cc: lkml <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: can't boot with reiserfs on linux-4.6.0+
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On Wed, May 25, 2016 at 05:30:22PM +0800, Jeff Chua wrote:
> On Wed, May 25, 2016 at 2:37 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > On Tue, May 24, 2016 at 04:59:02PM +0100, Al Viro wrote:
> >
> >> Umm...  Any chance of getting the function names to go with the addresses?
> >> I'll try to reproduce it here, but the things would be easier with that
> >> information...
> >
> > See if this fixes your reproducer.
> >
> > diff --git a/fs/xattr.c b/fs/xattr.c
> > index b11945e..49b8eab 100644
> > --- a/fs/xattr.c
> > +++ b/fs/xattr.c
> > @@ -667,6 +667,9 @@ xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
> >  {
> >         const struct xattr_handler *handler;
> >
> > +       if (!handlers)
> > +               return NULL;
> > +
> >         if (!*name)
> >                 return NULL;
> >
> 
> Tried, but doesn't work.

D'oh...  Since "vfs: Distinguish between full xattr names and proper prefixes"
we really need to return ERR_PTR() there (and I even have a patch from Andreas
fixing that if (!*name) return NULL; in my queue).  Combined delta to test
(that'll go as two commits, one mine, one his):

diff --git a/fs/xattr.c b/fs/xattr.c
index b11945e..fc81e77 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -655,6 +655,7 @@ strcmp_prefix(const char *a, const char *a_prefix)
  * operations to the correct xattr_handler.
  */
 #define for_each_xattr_handler(handlers, handler)		\
+	if (handlers)						\
 		for ((handler) = *(handlers)++;			\
 			(handler) != NULL;			\
 			(handler) = *(handlers)++)
@@ -668,7 +669,7 @@ xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
 	const struct xattr_handler *handler;
 
 	if (!*name)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 
 	for_each_xattr_handler(handlers, handler) {
 		const char *n;