linux-kernel - Re: 2.6.35-rc4-git3: Reported regressions from 2.6.34

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Message-ID: <20100709020440.GJ6405@nowhere>
Date:	Fri, 9 Jul 2010 04:04:42 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Maciej Rutecki <maciej.rutecki@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	Linux ACPI <linux-acpi@...r.kernel.org>,
	Linux PM List <linux-pm@...ts.linux-foundation.org>,
	Linux SCSI List <linux-scsi@...r.kernel.org>,
	Linux Wireless List <linux-wireless@...r.kernel.org>,
	DRI <dri-devel@...ts.sourceforge.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Shawn Starr <shawn.starr@...ers.com>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Dave Airlie <airlied@...hat.com>,
	"David S. Miller" <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>, Jens Axboe <axboe@...nel.dk>
Subject: Re: 2.6.35-rc4-git3: Reported regressions from 2.6.34

On Thu, Jul 08, 2010 at 06:34:25PM -0700, Linus Torvalds wrote:
> On Thu, Jul 8, 2010 at 4:33 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > Bug-Entry       : http://bugzilla.kernel.org/show_bug.cgi?id=16284
> > Subject         : Hitting WARN_ON in hw_breakpoint code
> > Submitter       : Paul Mackerras <paulus@...ba.org>
> > Date            : 2010-06-23 12:57 (16 days old)
> > Message-ID      : <20100623125740.GA3368@...ck.ozlabs.ibm.com>
> > References      : http://marc.info/?l=linux-kernel&m=127729789113432&w=2
> 
> This has "I have a fix, will post it very soon." in the thread from
> Frederic, but I'm not seeing anything else. Frederic?



Right. In fact it wasn't a regression. The per task breakpoint reservation
design was broken from the beginning and this warning has revealed the
problem. This only touched perf, and it did since perf support breakpoints.
Fortunately ptrace wasn't concerned by this problem, even not by side effects
of this.

The fix is invasive as it's a rewrite of a (little) part of the breakpoint
reservation. And since the symptom is only a warning and also breakpoints
never released from the constraint table (just a counter, no memory leak),
the fix is headed for 2.6.36.

It is ready in tip:/perf/core:

http://git.kernel.org/?p=linux/kernel/git/tip/linux-2.6-tip.git;a=commitdiff;h=45a73372efe4a63f44aa2e1125d4a777c2fdc8d8

I think this ticket can be safely closed.

Thanks.

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