[PATCH v2 5/5] padata: validate cpumask without removed CPU during offline

[Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>]

Configuring an instance's parallel mask without any online CPUs...

  echo 2 > /sys/kernel/pcrypt/pencrypt/parallel_cpumask
  echo 0 > /sys/devices/system/cpu/cpu1/online

...makes tcrypt mode=215 crash like this:

  divide error: 0000 [#1] SMP PTI
  CPU: 4 PID: 287 Comm: modprobe Not tainted 5.3.0-rc5-padata-base+ #7
  RIP: 0010:padata_do_parallel+0xfd/0x290
  Call Trace:
   pcrypt_do_parallel+0xed/0x1e0 [pcrypt]
   pcrypt_aead_encrypt+0xbf/0xd0 [pcrypt]
   crypto_aead_encrypt+0x1f/0x30
   do_mult_aead_op+0x4e/0xdf [tcrypt]
   test_mb_aead_speed.constprop.0.cold+0x226/0x564 [tcrypt]
   do_test+0x2280/0x4c16 [tcrypt]
   tcrypt_mod_init+0x55/0x1000 [tcrypt]
   ...

cpumask_weight() in padata_cpu_hash() returns 0 because the mask has no
CPUs.  The problem is __padata_remove_cpu() checks for valid masks too
early and so doesn't mark the instance PADATA_INVALID as expected, which
would have made padata_do_parallel() return error before doing the
division.

Fix by introducing a second padata CPU hotplug state before
CPUHP_BRINGUP_CPU so that __padata_remove_cpu() sees the online mask
without @cpu.  No need for the cpumask_clear_cpu()s since @cpu is
already missing from those masks.

Fixes: 33e54450683c ("padata: Handle empty padata cpumasks")
Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Steffen Klassert <steffen.klassert@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-crypto@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 include/linux/cpuhotplug.h |  1 +
 kernel/padata.c            | 21 ++++++++++++++-------
 2 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
index 068793a619ca..2d55cee638fc 100644
--- a/include/linux/cpuhotplug.h
+++ b/include/linux/cpuhotplug.h
@@ -59,6 +59,7 @@ enum cpuhp_state {
 	CPUHP_IOMMU_INTEL_DEAD,
 	CPUHP_LUSTRE_CFS_DEAD,
 	CPUHP_AP_ARM_CACHE_B15_RAC_DEAD,
+	CPUHP_PADATA_DEAD,
 	CPUHP_WORKQUEUE_PREP,
 	CPUHP_POWER_NUMA_PREPARE,
 	CPUHP_HRTIMERS_PREPARE,
diff --git a/kernel/padata.c b/kernel/padata.c
index 75e668fedd8d..5325e5978ee4 100644
--- a/kernel/padata.c
+++ b/kernel/padata.c
@@ -690,7 +690,7 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
 {
 	struct parallel_data *pd = NULL;
 
-	if (cpumask_test_cpu(cpu, cpu_online_mask)) {
+	if (!cpumask_test_cpu(cpu, cpu_online_mask)) {
 
 		if (!padata_validate_cpumask(pinst, pinst->cpumask.pcpu) ||
 		    !padata_validate_cpumask(pinst, pinst->cpumask.cbcpu))
@@ -702,9 +702,6 @@ static int __padata_remove_cpu(struct padata_instance *pinst, int cpu)
 			return -ENOMEM;
 
 		padata_replace(pinst, pd);
-
-		cpumask_clear_cpu(cpu, pd->cpumask.cbcpu);
-		cpumask_clear_cpu(cpu, pd->cpumask.pcpu);
 	}
 
 	return 0;
@@ -731,7 +728,7 @@ static int padata_cpu_online(unsigned int cpu, struct hlist_node *node)
 	return ret;
 }
 
-static int padata_cpu_prep_down(unsigned int cpu, struct hlist_node *node)
+static int padata_cpu_dead(unsigned int cpu, struct hlist_node *node)
 {
 	struct padata_instance *pinst;
 	int ret;
@@ -752,6 +749,7 @@ static enum cpuhp_state hp_online;
 static void __padata_free(struct padata_instance *pinst)
 {
 #ifdef CONFIG_HOTPLUG_CPU
+	cpuhp_state_remove_instance_nocalls(CPUHP_PADATA_DEAD, &pinst->node);
 	cpuhp_state_remove_instance_nocalls(hp_online, &pinst->node);
 #endif
 
@@ -938,6 +936,8 @@ static struct padata_instance *padata_alloc(struct workqueue_struct *wq,
 
 #ifdef CONFIG_HOTPLUG_CPU
 	cpuhp_state_add_instance_nocalls_cpuslocked(hp_online, &pinst->node);
+	cpuhp_state_add_instance_nocalls_cpuslocked(CPUHP_PADATA_DEAD,
+						    &pinst->node);
 #endif
 	return pinst;
 
@@ -984,17 +984,24 @@ static __init int padata_driver_init(void)
 	int ret;
 
 	ret = cpuhp_setup_state_multi(CPUHP_AP_ONLINE_DYN, "padata:online",
-				      padata_cpu_online,
-				      padata_cpu_prep_down);
+				      padata_cpu_online, NULL);
 	if (ret < 0)
 		return ret;
 	hp_online = ret;
+
+	ret = cpuhp_setup_state_multi(CPUHP_PADATA_DEAD, "padata:dead",
+				      NULL, padata_cpu_dead);
+	if (ret < 0) {
+		cpuhp_remove_multi_state(hp_online);
+		return ret;
+	}
 	return 0;
 }
 module_init(padata_driver_init);
 
 static __exit void padata_driver_exit(void)
 {
+	cpuhp_remove_multi_state(CPUHP_PADATA_DEAD);
 	cpuhp_remove_multi_state(hp_online);
 }
 module_exit(padata_driver_exit);
-- 
2.23.0