linux-kernel - Re: [PATCH -tip] x86: hw-breakpoints: Actually flush thread breakpoints in flush

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Message-ID: <20091009075311.GA5036@nowhere>
Date:	Fri, 9 Oct 2009 09:53:14 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Paul Mundt <lethal@...ux-sh.org>
Cc:	"K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip] x86: hw-breakpoints: Actually flush thread
	breakpoints in flush_thread().

On Fri, Oct 09, 2009 at 12:40:04PM +0900, Paul Mundt wrote:
> On Mon, Oct 05, 2009 at 04:19:55PM +0530, K.Prasad wrote:
> > On Mon, Oct 05, 2009 at 07:23:06PM +0900, Paul Mundt wrote:
> > > [ I noticed this whilst hacking up SH support, applies to the current
> > >   tracing/hw-breakpoints topic branch. ]
> > > 
> > > flush_thread() tries to do a TIF_DEBUG check before calling in to
> > > flush_thread_hw_breakpoint() (which subsequently clears the thread flag),
> > > but for some reason, the x86 code is manually clearing TIF_DEBUG
> > > immediately before the test, so this path will never be taken.
> > > 
> > > This kills off the erroneous clear_tsk_thread_flag() and lets
> > > flush_thread_hw_breakpoint() actually get invoked.
> > > 
> > 
> > Yes, this is wrong and we missed it. Thanks for fixing!
> > 
> > > Presumably folks were getting lucky with testing and the
> > > free_thread_info() -> free_thread_xstate() path was taking care of the
> > > flush there.
> > > 
> > > Signed-off-by: Paul Mundt <lethal@...ux-sh.org>
> > 
> > Acked-by: K.Prasad <prasad@...ux.vnet.ibm.com>
> > 
> > 
> Ingo, are you planning on picking this up? Or is there a hw-breakpoints
> tree somewhere outside of -tip that I'm unaware of?


Joining: Acked-by: Frederic Weisbecker <fweisbec@...il.com>

Even if a rewrite on top of perf event is planned, this is still a fix
on the current state. Something that the rewrite won't need to handle.

Thanks.

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