Re: WARNING: can't dereference registers at ffffc90004dfff60 for ip error_entry+0x7d/0xd0 (Re: [PATCH v2 00/18] Entry stack switching)

From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>, Josh Poimboeuf <jpoimboe@redhat.com>
Cc: X86 ML <x86@kernel.org>, Borislav Petkov <bpetkov@suse.de>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: WARNING: can't dereference registers at ffffc90004dfff60 for ip error_entry+0x7d/0xd0 (Re: [PATCH v2 00/18] Entry stack switching)
Date: Wed, 22 Nov 2017 08:43:52 +0100	[thread overview]
Message-ID: <20171122074352.6d2e6u7ynro3wrrf@gmail.com> (raw)
In-Reply-To: <20171122073907.mg6yayycfyvf4x4k@gmail.com>

* Ingo Molnar <mingo@kernel.org> wrote:

> 
> * Andy Lutomirski <luto@kernel.org> wrote:
> 
> > This sets up stack switching, including for SYSCALL.  I think it's
> > in decent shape.
> > 
> > Known issues:
> >  - I think we're going to want a way to turn the stack switching on and
> >    off either at boot time or at runtime.  It should be fairly straightforward
> >    to make it work.
> > 
> >  - I think the ORC unwinder isn't so good at dealing with stack overflows.
> >    It bails too early (I think), resulting in lots of ? entries.  This
> >    isn't a regression with this series -- it's just something that could
> >    be improved.
> 
> Note that with the attached config on an Intel testbox I get the following new ORC 
> unwinder warning during bootup:
> 
> [   12.200554] calling  ghash_pclmulqdqni_mod_init+0x0/0x54 @ 1
> [   12.209536] WARNING: can't dereference registers at ffffc90004dfff60 for ip error_entry+0x7d/0xd0
> [   12.231388] initcall ghash_pclmulqdqni_mod_init+0x0/0x54 returned 0 after 23480 usecs
> 
> Thanks,

Also note that the ORC warning goes away if CONFIG_PROVE_LOCKING is disabled.

Thanks,

	Ingo