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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: "Linus Torvalds" <torvalds@linux-foundation.org>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	"Josh Boyer" <jwboyer@fedoraproject.org>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	"Michel Dänzer" <michel@daenzer.net>,
	"Markus Trippelsdorf" <markus@trippelsdorf.de>,
	"Josh Stone" <jistone@redhat.com>
Subject: Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler
Date: Wed, 6 Aug 2014 09:34:56 -0700	[thread overview]
Message-ID: <CAADnVQ+mtZ3=Qv5Mz_P0unhTqaaf0KsyKXCNez33dhyGiFk=Mw@mail.gmail.com> (raw)
In-Reply-To: <20140806081441.GZ7393@tucnak.redhat.com>

On Wed, Aug 6, 2014 at 1:14 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Tue, Aug 05, 2014 at 03:36:39PM -0700, Linus Torvalds wrote:
d>> I don't understand how you guys can be so cavalier about a compiler
>> bug that has already resulted in actual real problems. You bring up
>
> I have no problem with a -fno-var-tracking-assignments workaround for
> compilers that have the PR61801 wrong-code bug.  What I have problem with
> is with disabling it even for compilers that have that bug fixed.
> That is in essence disabling a useful feature just because it could have
> other bugs.  If my memory serves me well, PR61801 is the only wrong-code
> I remember caused by -fvar-tracking-assignments during the 5 years since
> it has been introduced into gcc.  Sure, there have been several
> -fcompare-debug bugs, where we generated slightly different code between
> -g and -g0, and as you mentioned we have one still pending (Vladimir is
> working on it right now), but that is mainly relevant to the case where

I think gcc guys are taking a wrong lesson out of this. kernel doesn't
care too much whether gcc produces the same binary with -g and -g0.
kernel developers also don't care about amount debug info for variables,
but they care about hard to find compiler bugs. In this case sched2
mishap around debug_insn was a symptom. The root cause is lack
of attention to -mno-red-zone. Kernel is not another user space program
where data/control flow analysis is all compiler need to make things right.
-mno-red-zone lesson exposes lack of 'interrupt' concept in compiler.
I think there has to be some infra put in place to make sure that it's not
just a scheduling barrier. Otherwise next bug will pop much sooner
than 5 years and it will not be related to debug info at all.
In this sense Steven's perl script to detect red-zone violations did more
to re-enable var-tracking than -fcompare-debug fixes.

  parent reply	other threads:[~2014-08-06 16:34 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-30  1:48 [PATCH 3.15 00/37] 3.15.8-stable review Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 01/37] media: staging: tighten omap4iss dependencies Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 02/37] media: media: v4l2-core: v4l2-dv-timings.c: Cleaning up code wrong value used in aspect ratio Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 03/37] media: af9035: override tuner id when bad value set into eeprom Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 04/37] media: hdpvr: fix two audio bugs Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 05/37] media: tda10071: force modulation to QPSK on DVB-S Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 06/37] nfs: only show Posix ACLs in listxattr if actually present Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 07/37] xtensa: fix sysmem reservation at the end of existing block Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 08/37] block: provide compat ioctl for BLKZEROOUT Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 09/37] block: dont assume last put of shared tags is for the host Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 10/37] libata: support the ata host which implements a queue depth less than 32 Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 11/37] libata: introduce ata_host->n_tags to avoid oops on SAS controllers Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 12/37] s390/ptrace: fix PSW mask check Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 13/37] ahci: add support for the Promise FastTrak TX8660 SATA HBA (ahci mode) Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 14/37] blkcg: dont call into policy draining if root_blkg is already gone Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 15/37] tracing: Fix wraparound problems in "uptime" trace clock Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 16/37] zram: avoid lockdep splat by revalidate_disk Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 17/37] powerpc/pseries: dynamically added OF nodes need to call of_node_init Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 18/37] slab_common: fix the check for duplicate slab names Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 19/37] Input: synaptics - add min/max quirk for pnp-id LEN2002 (Edge E531) Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 20/37] Input: fix defuzzing logic Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 21/37] coredump: fix the setting of PF_DUMPCORE Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 22/37] fuse: s_time_gran fix Greg Kroah-Hartman
2014-07-30  1:48 ` [PATCH 3.15 23/37] fuse: add FUSE_NO_OPEN_SUPPORT flag to INIT Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 24/37] pinctrl: st: Fix irqmux handler Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 25/37] parisc: Remove SA_RESTORER define Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 26/37] hwmon: (smsc47m192) Fix temperature limit and vrm write operations Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 27/37] parport: fix menu breakage Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 28/37] fs: umount on symlink leaks mnt count Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 29/37] x86_32, entry: Store badsys error code in %eax Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 32/37] mm: hugetlb: fix copy_hugetlb_page_range() Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 34/37] hwrng: virtio - ensure reads happen after successful probe Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 35/37] mm: do not call do_fault_around for non-linear fault Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 36/37] nl80211: move set_qos_map command into split state Greg Kroah-Hartman
2014-07-30  1:49 ` [PATCH 3.15 37/37] platform_get_irq: Revert to platform_get_resource if of_irq_get fails Greg Kroah-Hartman
     [not found] ` <20140730014829.344302554@linuxfoundation.org>
2014-07-30  6:53   ` [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler Jakub Jelinek
2014-07-30  7:13     ` Markus Trippelsdorf
2014-07-30  7:21       ` Jakub Jelinek
2014-07-30  7:27         ` Markus Trippelsdorf
2014-07-30 15:47     ` Linus Torvalds
2014-08-05 11:31       ` Josh Boyer
2014-08-05 11:46         ` Markus Trippelsdorf
2014-08-05 15:24           ` Jakub Jelinek
2014-08-05 15:19         ` Greg Kroah-Hartman
2014-08-05 16:49         ` Linus Torvalds
2014-08-05 20:57           ` Josh Boyer
2014-08-05 21:07             ` Frank Ch. Eigler
2014-08-05 22:36               ` Linus Torvalds
2014-08-05 23:30                 ` Frank Ch. Eigler
2014-08-05 23:59                   ` Linus Torvalds
2014-10-06 21:05                     ` [PATCH] Kbuild: Add an option to enable GCC VTA Josh Stone
2014-08-06  8:14                 ` [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler Jakub Jelinek
2014-08-06 10:23                   ` Måns Rullgård
2014-08-06 10:23                     ` Måns Rullgård
2014-08-06 16:34                   ` Alexei Starovoitov [this message]
2014-07-30 11:58 ` [PATCH 3.15 00/37] 3.15.8-stable review Satoru Takeuchi
2014-07-30 11:58   ` Satoru Takeuchi
2014-07-30 15:50   ` Greg Kroah-Hartman
2014-07-30 16:09 ` Guenter Roeck
2014-07-30 22:23   ` Greg Kroah-Hartman

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