* Michael Ellerman [off-list ref] [2020-07-31 17:52:15]:

Srikar Dronamraju [off-list ref] writes:

quoted

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

quoted

Cc: linuxppc-dev <redacted>
Cc: LKML <redacted>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Anton Blanchard <redacted>
Cc: Oliver O'Halloran <oohall@gmail.com>
Cc: Nathan Lynch <redacted>
Cc: Michael Neuling <redacted>
Cc: Gautham R Shenoy <redacted>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <redacted>
Cc: Jordan Niethe <redacted>
Reviewed-by: Gautham R. Shenoy <redacted>
Signed-off-by: Srikar Dronamraju <redacted>
---
 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