From: Sven Schnelle <svens@linux.ibm.com>
Date: Tue, 15 Jun 2021 15:05:22 +0200
Subject: s390/topology: clear thread/group maps for offline cpus
Git-commit: 9e3d62d55bf455d4f9fdf2ede5c8756410c64102
Patch-mainline: v5.13
References: git-fixes

The current code doesn't clear the thread/group maps for offline
CPUs. This may cause kernel crashes like the one bewlow in common
code that assumes if a CPU has sibblings it is online.

Unable to handle kernel pointer dereference in virtual kernel address space

Call Trace:
 [<000000013a4b8c3c>] blk_mq_map_swqueue+0x10c/0x388
([<000000013a4b8bcc>] blk_mq_map_swqueue+0x9c/0x388)
 [<000000013a4b9300>] blk_mq_init_allocated_queue+0x448/0x478
 [<000000013a4b9416>] blk_mq_init_queue+0x4e/0x90
 [<000003ff8019d3e6>] loop_add+0x106/0x278 [loop]
 [<000003ff801b8148>] loop_init+0x148/0x1000 [loop]
 [<0000000139de4924>] do_one_initcall+0x3c/0x1e0
 [<0000000139ef449a>] do_init_module+0x6a/0x2a0
 [<0000000139ef61bc>] __do_sys_finit_module+0xa4/0xc0
 [<0000000139de9e6e>] do_syscall+0x7e/0xd0
 [<000000013a8e0aec>] __do_syscall+0xbc/0x110
 [<000000013a8ee2e8>] system_call+0x78/0xa0

Fixes: 52aeda7accb6 ("s390/topology: remove offline CPUs from CPU topology masks")
Cc: <stable@kernel.org> # 5.7+
Reported-by: Marius Hillenbrand <mhillen@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
[ ptesarik: Adapted, because SLE15-SP3 does not contain upstream
  commit da6d2c289dbe8871f1977bf7c348309d37b867b0. ]
Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 arch/s390/kernel/topology.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/arch/s390/kernel/topology.c
+++ b/arch/s390/kernel/topology.c
@@ -69,7 +69,10 @@ static cpumask_t cpu_group_map(struct ma
 {
 	cpumask_t mask;
 
-	cpumask_copy(&mask, cpumask_of(cpu));
+	cpumask_clear(&mask);
+	if (!cpu_online(cpu))
+		goto out;
+	cpumask_set_cpu(cpu, &mask);
 	switch (topology_mode) {
 	case TOPOLOGY_MODE_HW:
 		while (info) {
@@ -88,10 +91,10 @@ static cpumask_t cpu_group_map(struct ma
 	default:
 		/* fallthrough */
 	case TOPOLOGY_MODE_SINGLE:
-		cpumask_copy(&mask, cpumask_of(cpu));
 		break;
 	}
 	cpumask_and(&mask, &mask, cpu_online_mask);
+out:
 	return mask;
 }
 
@@ -100,7 +103,10 @@ static cpumask_t cpu_thread_map(unsigned
 	cpumask_t mask;
 	int i;
 
-	cpumask_copy(&mask, cpumask_of(cpu));
+	cpumask_clear(&mask);
+	if (!cpu_online(cpu))
+		return mask;
+	cpumask_set_cpu(cpu, &mask);
 	if (topology_mode != TOPOLOGY_MODE_HW)
 		return mask;
 	cpu -= cpu % (smp_cpu_mtid + 1);