linux-kernel - Re: [PATCH 3/3] perf,hw_breakpoint,kgdb: No mutex taken for kerneldebugger

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Date:	Thu, 28 Jan 2010 21:09:56 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jason Wessel <jason.wessel@...driver.com>
Cc:	linux-kernel@...r.kernel.org, kgdb-bugreport@...ts.sourceforge.net,
	mingo@...e.hu, "K.Prasad" <prasad@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 3/3] perf,hw_breakpoint,kgdb: No mutex taken for
	kerneldebugger

On Thu, Jan 28, 2010 at 11:49:14AM -0600, Jason Wessel wrote:
> Frederic Weisbecker wrote:
> >> +static int hw_break_release_slot(int breakno)
> >> +{
> >> +	struct perf_event **pevent;
> >> +	int ret;
> >> +	int cpu;
> >> +
> >> +	for_each_online_cpu(cpu) {
> >> +		pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
> >> +		ret = dbg_release_bp_slot(*pevent);
> >>     
> >
> >
> >
> > So, you are missing some return errors there. Actually, a slot
> > release shouldn't return an error.
> >
> >
> >   
> 
> This is a trick so to speak.   Either all the slot releases will return
> 0 or -1 depending on if the mutex is available, so it is not really
> missed. 



Oh right, I forgot everything was freezed here :)


 
> > Ok, best effort fits well for reserve, but is certainly not
> > suitable for release. We can't leave a fake occupied slot like
> > this. If it fails, we should do this asynchronously, using the
> > usual release_bp_slot, may be toward the workqueues.
> >
> >
> >
> >   
> 
> If it fails the debugger tried to remove it again later.   It seems to
> me like it is a don't care corner case.   You get a printk if it ever
> does happen (which it really shouldn't).



Yeah truly it's a corner case, especially if the debugger can handle that
later.

May be just add a comment so that future reviewers don't stick to
this part.

 
Thanks!

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