linux-kernel - Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations)

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Date:	Mon, 18 Apr 2016 16:21:42 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	James Bottomley <James.Bottomley@...senpartnership.com>,
	Thomas Graf <tgraf@...g.ch>,
	Peter Zijlstra <peterz@...radead.org>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	linux-scsi <linux-scsi@...r.kernel.org>, jamborm@....gnu.org
Subject: Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations)

On Monday 18 April 2016 09:12:41 Josh Poimboeuf wrote:
> On Mon, Apr 18, 2016 at 04:07:51PM +0200, Arnd Bergmann wrote:
> > On Monday 18 April 2016 08:39:32 Josh Poimboeuf wrote:
> > > 
> > > I agree.  So how should we work around the bug in this case?  There have
> > > been several suggestions:
> > > 
> > > - change wwn_to_u64() to __always_inline
> > > 
> > > - change qla2x00_get_host_fabric_name() to skip the unnecessary call to
> > >   wwn_to_u64()
> > > 
> > > - revert one of the two commits:
> > >   bc27fb68aaad ("include/uapi/linux/byteorder, swab: force inlining of some byteswap operations")
> > >   ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 for wwn access")
> > 
> > What about the patch to change get_unaligned_be64() that I posted?
> > 
> > I think we want to merge that anyway, I just don't know if that helps
> > with this particular problem as well.
> 
> I replied to your other email about that -- it doesn't seem to help this
> issue.
> 

Ok, I see. I had problems with my mail server last week, your reply
must have been a victim of that as I never saw it (found it on the
web archive now).

I'd vote for the wwn_to_u64 change then as it should prevent the
same thing from happining in other drivers. I would prefer not to
see ef3fb2422ffe reverted, as that works around another gcc-6 bug
on ARM.

	Arnd