From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Denys Vlasenko <dvlasenk@redhat.com>,
Himanshu Madhani <himanshu.madhani@qlogic.com>
Cc: qla2xxx-upstream@qlogic.com, Josh Poimboeuf <jpoimboe@redhat.com>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646
Date: Fri, 15 Apr 2016 12:05:26 -0700 [thread overview]
Message-ID: <1460747126.2331.28.camel@HansenPartnership.com> (raw)
In-Reply-To: <57113959.8050103@redhat.com>
On Fri, 2016-04-15 at 20:56 +0200, Denys Vlasenko wrote:
> On 04/15/2016 04:40 PM, James Bottomley wrote:
> > On Fri, 2016-04-15 at 12:36 +0200, Denys Vlasenko wrote:
> > > More info here:
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646
> >
> > This bug is under investigation, so I'd rather not alter code for a
> > gcc
> > bug until we know if we can supply options to fix it rather than
> > changing code.
>
>
> Background. The bug exists in gcc for 2 years, but it is rather
> hard to trigger, so nobody noticed.
We know this ... linux-scsi is on the cc for the other thread on this.
> Unfortunately for kernel, these two commits landed in Linus tree
> in March 16 and 17:
>
>
> On 04/13/2016 05:36 AM, Josh Poimboeuf wrote:
> > It occurs with the combination of the following two recent commits:
> >
> > - bc27fb68aaad ("include/uapi/linux/byteorder, swab: force inlining
> > of some byteswap operations")
> > - ef3fb2422ffe ("scsi: fc: use get/put_unaligned64 for wwn access")
>
>
> and now *many* users of qla2x00 and new-ish gcc are going to
> very much notice it, as their kernels will start crashing reliably.
>
> The commits can be reverted, sure, but they per se do not contain
> anything unusual. They, together with not very typical construct
> in qla2x00_get_host_fabric_name, one
> which boils down to "swab64p(constant_array_of_8_bytes)",
> just happen to nudge gcc in a right way to finally trigger the bug.
>
> So I came with another idea how to forestall the imminent deluge of
> qla2x00 oops reports - this patch.
There are actually a raft of checkers that run the upstream code which
aren't seeing any problem; likely because the code is harder to trigger
than you think. So, lets wait until the resolution of the other thread
before we panic, especially since we're only at -rc3.
James
next prev parent reply other threads:[~2016-04-15 19:05 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-15 10:36 [PATCH] qla2xxx: rewrite code to avoid hitting gcc bug 70646 Denys Vlasenko
2016-04-15 14:40 ` James Bottomley
2016-04-15 18:56 ` Denys Vlasenko
2016-04-15 19:05 ` James Bottomley [this message]
2016-04-15 20:02 ` Josh Poimboeuf
2016-04-15 21:15 ` James Bottomley
2016-04-15 21:09 ` Denys Vlasenko
2016-04-15 21:25 ` James Bottomley
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1460747126.2331.28.camel@HansenPartnership.com \
--to=james.bottomley@hansenpartnership.com \
--cc=dvlasenk@redhat.com \
--cc=himanshu.madhani@qlogic.com \
--cc=jpoimboe@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-scsi@vger.kernel.org \
--cc=qla2xxx-upstream@qlogic.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).