[PATCH 3/2] padata: initialize usable masks to reflect offlined CPU

[Daniel Jordan <daniel.m.jordan@oracle.com>]

__padata_remove_cpu clears the offlined CPU from the usable masks after
padata_alloc_pd has initialized pd->cpu, which means pd->cpu could be
initialized to this CPU, causing padata to wait indefinitely for the
next job in padata_get_next.

Make the usable masks reflect the offline CPU when they're established
in padata_setup_cpumasks so pd->cpu is initialized properly.

Fixes: 6fc4dbcf0276 ("padata: Replace delayed timer with immediate workqueue in padata_reorder")
Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Cc: linux-crypto@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
---

Hi, one more edge case.  All combinations of CPUs among
parallel_cpumask, serial_cpumask, and CPU hotplug have now been tested
in a 4-CPU VM, and an 8-CPU VM has run with random combinations of these
settings for over an hour.

 kernel/padata.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/padata.c b/kernel/padata.c
index 01460ea1d160..c1002ac4720c 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -702,17 +702,27 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
 	struct parallel_data *pd = NULL;
 
 	if (cpumask_test_cpu(cpu, cpu_online_mask)) {
+		cpumask_var_t pcpu, cbcpu;
+
 		__padata_stop(pinst);
 
-		pd = padata_alloc_pd(pinst, pinst->cpumask.pcpu,
-				     pinst->cpumask.cbcpu);
+		/*
+		 * padata_alloc_pd uses cpu_online_mask to get the usable
+		 * masks, but @cpu hasn't been removed from it yet, so use
+		 * temporary masks that exclude @cpu so the usable masks show
+		 * @cpu as offline for pd->cpu's initialization.
+		 */
+		cpumask_copy(pcpu, pinst->cpumask.pcpu);
+		cpumask_copy(cbcpu, pinst->cpumask.cbcpu);
+		cpumask_clear_cpu(cpu, cbcpu);
+		cpumask_clear_cpu(cpu, pcpu);
+
+		pd = padata_alloc_pd(pinst, pcpu, cbcpu);
 		if (!pd)
 			return -ENOMEM;
 
 		padata_replace(pinst, pd);
 
-		cpumask_clear_cpu(cpu, pd->cpumask.cbcpu);
-		cpumask_clear_cpu(cpu, pd->cpumask.pcpu);
 		if (padata_validate_cpumask(pinst, pd->cpumask.pcpu) &&
 		    padata_validate_cpumask(pinst, pd->cpumask.cbcpu))
 			__padata_start(pinst);
-- 
2.22.0