Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk

From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
	Pavel Machek <pavel@ucw.cz>,
	Linux PM list <linux-pm@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	shuzzle@mailbox.org
Subject: Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk
Date: Wed, 27 Jul 2016 00:42:30 +0200	[thread overview]
Message-ID: <4852923.iQFmCCTKQM@vostro.rjw.lan> (raw)
In-Reply-To: <20160726215319.twz22r5kbkpsgzfg@treble>

On Tuesday, July 26, 2016 04:53:19 PM Josh Poimboeuf wrote:
> On Tue, Jul 26, 2016 at 10:15:39PM +0200, Rafael J. Wysocki wrote:
> > On Tuesday, July 26, 2016 09:39:05 AM Josh Poimboeuf wrote:
> > > On Tue, Jul 26, 2016 at 01:32:28PM +0200, Rafael J. Wysocki wrote:
> > > > Hi,
> > > > 
> > > > The following commit:
> > > > 
> > > > commit 13523309495cdbd57a0d344c0d5d574987af007f
> > > > Author: Josh Poimboeuf <jpoimboe@redhat.com>
> > > > Date:   Thu Jan 21 16:49:21 2016 -0600
> > > > 
> > > >     x86/asm/acpi: Create a stack frame in do_suspend_lowlevel()
> > > >     
> > > >     do_suspend_lowlevel() is a callable non-leaf function which doesn't
> > > >     honor CONFIG_FRAME_POINTER, which can result in bad stack traces.
> > > >     
> > > >     Create a stack frame for it when CONFIG_FRAME_POINTER is enabled.
> > > > 
> > > > is reported to cause a resume-from-hibernation regression due to an attempt
> > > > to execute an NX page (we've seen quite a bit of that recently).
> > > > 
> > > > I'm asking the reporter to try 4.7, but if the problem is still there, we'll
> > > > need to revert the above I'm afraid.
> > 
> > So the bug is still there in 4.7 and it goes away after reverting the above
> > commit.  I guess I'll send a revert then.
> 
> Hm, the code in wakeup_64.S seems quite magical, but I can't figure out
> why this change causes a panic.  Is it really causing the panic or is it
> uncovering some other bug?

It doesn't matter really.

It surely interacts with something in a really odd way, but that only means
that its impact goes far beyond what was expected when it was applied.  Its
changelog is inadequate as a result and so on.

> Maybe we should hold off on reverting until we understand the issue.

Which very well may take forever.

And AFAICS this is a fix for a theoretical issue and it *reliably* triggers a
very practical kernel panic for this particular reporter.  I'd rather live
with the theoretical issue unfixed to be honest.

Thanks,
Rafael