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From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Lynch <nathanl@linux.ibm.com>,
	Gautham R Shenoy <ego@linux.vnet.ibm.com>,
	Michael Neuling <mikey@neuling.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Jordan Niethe <jniethe5@gmail.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Nicholas Piggin <npiggin@gmail.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Oliver O'Halloran <oohall@gmail.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH v4 08/10] powerpc/smp: Allocate cpumask only after searching thread group
Date: Fri, 31 Jul 2020 15:19:38 +0530	[thread overview]
Message-ID: <20200731094938.GA18776@linux.vnet.ibm.com> (raw)
In-Reply-To: <87zh7g3yvk.fsf@mpe.ellerman.id.au>

* Michael Ellerman <mpe@ellerman.id.au> [2020-07-31 17:52:15]:

> Srikar Dronamraju <srikar@linux.vnet.ibm.com> writes:
> > If allocated earlier and the search fails, then cpumask need to be
> > freed. However cpu_l1_cache_map can be allocated after we search thread
> > group.
> 
> It's not freed anywhere AFAICS?
> 

Yes, its never freed. Infact we are never checking if
zalloc_cpumask_var_node fails. Its not just this cpumask, but historically
all the other existing cpumasks in arch/powerpc/kernel/smp.c are never
freed/checked. I did dig into this a bit and it appears that ..
(Please do correct me if I am wrong!! )

Powerpc using cpumask_var_t for all of the percpu variables. And it dont seem
to enable CONFIG_CPUMASK_OFFSTACK even from the MAXSMP config.

So from include/linux/cpumask.h

typedef struct cpumask cpumask_var_t[1];
and
zalloc_cpumask_var_node ends up being cpumask_clear

So I think we are historically we seem to assume we are always
!CPUMASK_OFFSTACK and hence we dont need to check for return as well as
free..

I would look forward to your comments on how we should handle this going
forward. But I would keep this the same for this patchset.

One of the questions that I have is if we most likely are to be in
!CONFIG_CPUMASK_OFFSTACK, then should be migrate to cpumask_t for percpu
variables. 
 
The reason being we end up using NR_CPU cpumask for each percpu cpumask
variable instead of using NR_CPU cpumask_t pointer.

> And even after this change there's still an error path that doesn't free
> it, isn't there?
> 
> cheers
> 
> > Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
> > Cc: LKML <linux-kernel@vger.kernel.org>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Nicholas Piggin <npiggin@gmail.com>
> > Cc: Anton Blanchard <anton@ozlabs.org>
> > Cc: Oliver O'Halloran <oohall@gmail.com>
> > Cc: Nathan Lynch <nathanl@linux.ibm.com>
> > Cc: Michael Neuling <mikey@neuling.org>
> > Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Valentin Schneider <valentin.schneider@arm.com>
> > Cc: Jordan Niethe <jniethe5@gmail.com>
> > Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> > Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> > ---
> >  arch/powerpc/kernel/smp.c | 7 +++----
> >  1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > index 698000c7f76f..dab96a1203ec 100644
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -797,10 +797,6 @@ static int init_cpu_l1_cache_map(int cpu)
> >  	if (err)
> >  		goto out;
> >  
> > -	zalloc_cpumask_var_node(&per_cpu(cpu_l1_cache_map, cpu),
> > -				GFP_KERNEL,
> > -				cpu_to_node(cpu));
> > -
> >  	cpu_group_start = get_cpu_thread_group_start(cpu, &tg);
> >  
> >  	if (unlikely(cpu_group_start == -1)) {
> > @@ -809,6 +805,9 @@ static int init_cpu_l1_cache_map(int cpu)
> >  		goto out;
> >  	}
> >  
> > +	zalloc_cpumask_var_node(&per_cpu(cpu_l1_cache_map, cpu),
> > +				GFP_KERNEL, cpu_to_node(cpu));
> > +
> >  	for (i = first_thread; i < first_thread + threads_per_core; i++) {
> >  		int i_group_start = get_cpu_thread_group_start(i, &tg);
> >  
> > -- 
> > 2.17.1

-- 
Thanks and Regards
Srikar Dronamraju

  reply	other threads:[~2020-07-31  9:51 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-27  5:32 [PATCH v4 00/10] Coregroup support on Powerpc Srikar Dronamraju
2020-07-27  5:32 ` [PATCH v4 01/10] powerpc/smp: Fix a warning under !NEED_MULTIPLE_NODES Srikar Dronamraju
2020-07-27  5:32 ` [PATCH v4 02/10] powerpc/smp: Merge Power9 topology with Power topology Srikar Dronamraju
2020-07-27  5:32 ` [PATCH v4 03/10] powerpc/smp: Move powerpc_topology above Srikar Dronamraju
2020-07-27  5:32 ` [PATCH v4 04/10] powerpc/smp: Move topology fixups into a new function Srikar Dronamraju
2020-07-27  5:32 ` [PATCH v4 05/10] powerpc/smp: Dont assume l2-cache to be superset of sibling Srikar Dronamraju
2020-07-27  5:32 ` [PATCH v4 06/10] powerpc/smp: Generalize 2nd sched domain Srikar Dronamraju
2020-07-30  5:55   ` Gautham R Shenoy
2020-07-31  7:45   ` Michael Ellerman
2020-07-31  9:29     ` Srikar Dronamraju
2020-07-31 12:22       ` Michael Ellerman
2020-07-27  5:32 ` [PATCH v4 07/10] Powerpc/numa: Detect support for coregroup Srikar Dronamraju
2020-07-31  7:49   ` Michael Ellerman
2020-07-31  9:18     ` Srikar Dronamraju
2020-07-31 11:31       ` Michael Ellerman
2020-07-27  5:32 ` [PATCH v4 08/10] powerpc/smp: Allocate cpumask only after searching thread group Srikar Dronamraju
2020-07-31  7:52   ` Michael Ellerman
2020-07-31  9:49     ` Srikar Dronamraju [this message]
2020-07-31 12:14       ` Michael Ellerman
2020-07-27  5:32 ` [PATCH v4 09/10] Powerpc/smp: Create coregroup domain Srikar Dronamraju
2020-07-27 18:52   ` Gautham R Shenoy
2020-07-28 15:03   ` Valentin Schneider
2020-07-29  6:13     ` Srikar Dronamraju
2020-07-31  1:05       ` Valentin Schneider
2020-08-03  6:01         ` Srikar Dronamraju
2020-07-31  7:36       ` Gautham R Shenoy
2020-07-27  5:32 ` [PATCH v4 10/10] powerpc/smp: Implement cpu_to_coregroup_id Srikar Dronamraju
2020-07-31  8:02   ` Michael Ellerman
2020-07-31  9:58     ` Srikar Dronamraju
2020-07-31 11:29       ` Michael Ellerman
2020-07-30 17:22 ` [PATCH v4 00/10] Coregroup support on Powerpc Srikar Dronamraju
  -- strict thread matches above, loose matches on Subject: below --
2020-07-27  5:17 Srikar Dronamraju
2020-07-27  5:18 ` [PATCH v4 08/10] powerpc/smp: Allocate cpumask only after searching thread group Srikar Dronamraju

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