From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Denys Vlasenko <dvlasenk@redhat.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
Thomas Graf <tgraf@suug.ch>,
Peter Zijlstra <peterz@infradead.org>,
David Rientjes <rientjes@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
linux-scsi <linux-scsi@vger.kernel.org>,
jamborm@gcc.gnu.org
Subject: Re: This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations)
Date: Mon, 18 Apr 2016 08:39:32 -0500 [thread overview]
Message-ID: <20160418133932.cnpxai32qn665un3@treble> (raw)
In-Reply-To: <20160416090332.GA30613@gmail.com>
On Sat, Apr 16, 2016 at 11:03:32AM +0200, Ingo Molnar wrote:
>
> * Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> > > I don't think we know yet if there's a reliable way to turn the bug off.
> > >
> > > Also, according to the gcc guys, this bug won't always result in a
> > > truncated function, and may sometimes just make some inline function
> > > call sites disappear:
> > >
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646#c14
> > >
> > > though I haven't been able to confirm that experimentally. But if it's
> > > true, that means that objtool won't be able to detect all cases of the
> > > bug and some function calls may just silently disappear!
> > >
> > > There's a lot of activity in the bug now, so hopefully they'll be able
> > > to tell us soon if there's a reliable way to avoid it and/or detect it.
> > >
> > > BTW, Denys posted a workaround patch for the qla2xxxx code:
> > >
> > > https://lkml.kernel.org/r/1460716583-15673-1-git-send-email-dvlasenk@redhat.com
> >
> > Martin Jambor wrote a succinct summary of the conditions needed for this
> > bug:
> >
> > "This bug can occur when an inlineable function containing a call to
> > __builtin_constant_p, which checks a parameter or a value it
> > references and a (possibly indirect) caller of the function actually
> > passes a constant, but stores it using a type of a different size."
> >
> > So to prevent it from happening elsewhere in the kernel, it sounds like
> > we'd have to either remove all uses of __builtin_constant_p() or disable
> > inlining completely.
> >
> > There's also no reliable way to detect the bug has occurred, though
> > objtool will detect it in cases when the function gets truncated.
>
> So it appears to me that due to the hard to detect nature of the GCC bug the fix
> will probably be backported by them, so I think we should be fine with relying on
> objtool to detect weird code sequences in the kernel, and should work around
> specific instances of the bug.
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")
--
Josh
next prev parent reply other threads:[~2016-04-18 13:39 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-04 19:45 [PATCH] asm-generic: force inlining of some atomic_long operations Denys Vlasenko
2016-02-04 19:45 ` [PATCH] force inlining of some byteswap operations Denys Vlasenko
2016-02-05 7:28 ` Ingo Molnar
2016-04-13 3:36 ` This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Josh Poimboeuf
2016-04-13 12:12 ` Denys Vlasenko
2016-04-13 12:36 ` Josh Poimboeuf
2016-04-13 15:15 ` Josh Poimboeuf
2016-04-13 16:55 ` James Bottomley
2016-04-13 17:10 ` Josh Poimboeuf
2016-04-14 15:29 ` Denys Vlasenko
2016-04-14 15:57 ` Josh Poimboeuf
2016-04-14 17:09 ` Denys Vlasenko
2016-04-15 5:45 ` Ingo Molnar
2016-04-15 13:47 ` Josh Poimboeuf
2016-04-15 22:20 ` Josh Poimboeuf
2016-04-16 9:03 ` Ingo Molnar
2016-04-18 13:39 ` Josh Poimboeuf [this message]
2016-04-18 14:07 ` Arnd Bergmann
2016-04-18 14:12 ` Josh Poimboeuf
2016-04-18 14:21 ` Arnd Bergmann
2016-04-19 8:52 ` Ingo Molnar
2016-04-19 13:56 ` [PATCH] scsi: fc: force inlining of wwn conversion functions Josh Poimboeuf
2016-04-22 23:17 ` Quinn Tran
2016-04-25 16:07 ` Josh Poimboeuf
2016-04-26 2:40 ` Martin K. Petersen
2016-04-26 3:37 ` James Bottomley
2016-04-26 7:22 ` Arnd Bergmann
2016-04-26 8:35 ` Christoph Hellwig
2016-04-26 10:05 ` Arnd Bergmann
2016-04-26 13:06 ` Martin K. Petersen
2016-04-26 15:58 ` Arnd Bergmann
2016-04-26 22:36 ` James Bottomley
2016-04-27 0:44 ` Martin K. Petersen
2016-04-27 11:05 ` Martin Jambor
2016-04-27 21:34 ` Arnd Bergmann
2016-04-28 14:58 ` Chris Metcalf
2016-04-28 15:23 ` Arnd Bergmann
2016-04-28 15:48 ` Chris Metcalf
2016-04-27 22:00 ` [PATCH, RFT] byteswap: try to avoid __builtin_constant_p gcc bug Arnd Bergmann
2016-04-27 22:11 ` Josh Poimboeuf
2016-04-28 16:27 ` Quinn Tran
2016-04-16 7:42 ` This patch triggers a bad gcc bug (was Re: [PATCH] force inlining of some byteswap operations) Arnd Bergmann
2016-04-18 13:22 ` Josh Poimboeuf
2016-02-04 19:45 ` [PATCH] force inlining of unaligned byteswap operations Denys Vlasenko
2016-02-05 7:28 ` Ingo Molnar
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