Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-06 Thread Alexei Starovoitov
On Wed, Aug 6, 2014 at 1:14 AM, Jakub Jelinek 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-va

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-06 Thread Måns Rullgård
Jakub Jelinek writes: > There have been several man-years of work to get from the 25% var coverage > to 67%, several DWARF extensions (most of them to be available in DWARF5 or > work in progress on that) and with -fno-var-tracking-assignments that is > just returned to the old state. This is a

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-06 Thread Jakub Jelinek
On Tue, Aug 05, 2014 at 03:36:39PM -0700, Linus Torvalds wrote: > On Tue, Aug 5, 2014 at 2:07 PM, Frank Ch. Eigler wrote: > > > > Actually, "perf probe" does (via HAVE_DWARF_SUPPORT), to place probes > > and to extract variables at those probes, much as systemtap does. > > Without var-tracking, pr

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Linus Torvalds
On Tue, Aug 5, 2014 at 4:30 PM, Frank Ch. Eigler wrote: > > Would you consider a patch that does a gcc COMPARE_DEBUG-based test? Yes. But as mentioned, we don't have a really good way to do that. I guess we can do something similar to what "cc-option" does, but that will end up doing it for every

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Frank Ch. Eigler
Hi - On Tue, Aug 05, 2014 at 03:36:39PM -0700, Linus Torvalds wrote: > > Actually, "perf probe" does (via HAVE_DWARF_SUPPORT), to place probes > > and to extract variables at those probes, much as systemtap does. > > Without var-tracking, probes placed at most interior points of > > functions will

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Linus Torvalds
On Tue, Aug 5, 2014 at 2:07 PM, Frank Ch. Eigler wrote: > > Actually, "perf probe" does (via HAVE_DWARF_SUPPORT), to place probes > and to extract variables at those probes, much as systemtap does. > Without var-tracking, probes placed at most interior points of > functions will make variables ina

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Frank Ch. Eigler
Hi - > >>. I don't disagree it should be > >> disabled by default, but making it unconditional is going to force the > >> distributions that care about perf, systemtap, and debuggers to > >> manually revert this. > > > > Bah. I bet I use 'perf' more than most, and it doesn't care about > > debug

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Josh Boyer
On Tue, Aug 5, 2014 at 12:49 PM, Linus Torvalds wrote: > On Tue, Aug 5, 2014 at 4:31 AM, Josh Boyer wrote: >> >> Sorry to bring this back up after the fact, but it's important for a >> number of things in various distros > > You said that before, and I ignored you before, because you didn't > act

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Linus Torvalds
On Tue, Aug 5, 2014 at 4:31 AM, Josh Boyer wrote: > > Sorry to bring this back up after the fact, but it's important for a > number of things in various distros You said that before, and I ignored you before, because you didn't actually give any examples. >. I don't disagree it should be > disa

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Jakub Jelinek
On Tue, Aug 05, 2014 at 01:46:49PM +0200, Markus Trippelsdorf wrote: > On 2014.08.05 at 07:31 -0400, Josh Boyer wrote: > > Sorry to bring this back up after the fact, but it's important for a > > number of things in various distros. I don't disagree it should be > > disabled by default, but making

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Greg Kroah-Hartman
On Tue, Aug 05, 2014 at 07:31:22AM -0400, Josh Boyer wrote: > On Wed, Jul 30, 2014 at 11:47 AM, Linus Torvalds > wrote: > > On Tue, Jul 29, 2014 at 11:53 PM, Jakub Jelinek wrote: > >> > >> IMNSHO this is a too big hammer approach. The bug happened on a single > >> file only (right?) > > > > Very

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Markus Trippelsdorf
On 2014.08.05 at 07:31 -0400, Josh Boyer wrote: > Sorry to bring this back up after the fact, but it's important for a > number of things in various distros. I don't disagree it should be > disabled by default, but making it unconditional is going to force the > distributions that care about perf,

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-08-05 Thread Josh Boyer
On Wed, Jul 30, 2014 at 11:47 AM, Linus Torvalds wrote: > On Tue, Jul 29, 2014 at 11:53 PM, Jakub Jelinek wrote: >> >> IMNSHO this is a too big hammer approach. The bug happened on a single >> file only (right?) > > Very dubious. We happened to see it in a single case, and _maybe_ that > was the

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-07-30 Thread Linus Torvalds
On Tue, Jul 29, 2014 at 11:53 PM, Jakub Jelinek wrote: > > IMNSHO this is a too big hammer approach. The bug happened on a single > file only (right?) Very dubious. We happened to see it in a single case, and _maybe_ that was the only one in the whole kernel. But it's much more likely that it wa

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-07-30 Thread Markus Trippelsdorf
On 2014.07.30 at 09:21 +0200, Jakub Jelinek wrote: > On Wed, Jul 30, 2014 at 09:13:08AM +0200, Markus Trippelsdorf wrote: > > On 2014.07.30 at 08:53 +0200, Jakub Jelinek wrote: > > > On Tue, Jul 29, 2014 at 06:49:09PM -0700, Greg Kroah-Hartman wrote: > > > > 3.15-stable review patch. If anyone has

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-07-30 Thread Jakub Jelinek
On Wed, Jul 30, 2014 at 09:13:08AM +0200, Markus Trippelsdorf wrote: > On 2014.07.30 at 08:53 +0200, Jakub Jelinek wrote: > > On Tue, Jul 29, 2014 at 06:49:09PM -0700, Greg Kroah-Hartman wrote: > > > 3.15-stable review patch. If anyone has any objections, please let me > > > know. > > > > IMNSHO

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-07-30 Thread Markus Trippelsdorf
On 2014.07.30 at 08:53 +0200, Jakub Jelinek wrote: > On Tue, Jul 29, 2014 at 06:49:09PM -0700, Greg Kroah-Hartman wrote: > > 3.15-stable review patch. If anyone has any objections, please let me know. > > IMNSHO this is a too big hammer approach. The bug happened on a single > file only (right?)

Re: [PATCH 3.15 33/37] Fix gcc-4.9.0 miscompilation of load_balance() in scheduler

2014-07-29 Thread Jakub Jelinek
On Tue, Jul 29, 2014 at 06:49:09PM -0700, Greg Kroah-Hartman wrote: > 3.15-stable review patch. If anyone has any objections, please let me know. IMNSHO this is a too big hammer approach. The bug happened on a single file only (right?), so if anything, IMHO it could be disabled for that single f