Re: [PATCH] locking bug in fib_semantics.c

[David Miller <davem@davemloft.net>]

From: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Date: Thu, 17 Aug 2006 13:36:15 +0400

> Found in 2.4 by Yixin Pan <yxpan@hotmail.com>. Why do we need lockdep,
> when sharp-sighted eyes are available? :-)

Lockdep can only tell us about code paths which actually have been
run, so it shows that nobody running lockdep has had a redirect arrive
on a non-shared-media device marked for secure redirects :)

But such a code path would only need to run once for lockdep to catch
it.

> > When I read fib_semantics.c of Linux-2.4.32, write_lock(&fib_info_lock) =
> > is used in fib_release_info() instead of write_lock_bh(&fib_info_lock).  =
> > Is the following case possible: a BH interrupts fib_release_info() while =
> > holding the write lock, and calls ip_check_fib_default() which calls =
> > read_lock(&fib_info_lock), and spin forever.
> 
> Signed-off-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>

Good spotting.  Patch applied, and I'll push this to -stable too.

Thanks a lot.