[PATCH] powerpc/smp: Handle missing ibm,thread-groups in parse_thread_groups()

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

Power systems can have ibm,thread-groups properly absent like in one of
the PowerNV Power9 boxes where there was a warning splat reported on
7.4-rc2:

  WARNING: mm/slub.c:5459 at ___kmalloc_large_node+0x174/0x1a0, CPU#124: swapper/124/1
  ...
  Call Trace:
   __kmalloc_noprof+0x490/0x690
   _kzalloc_noprof.constprop.0+0x1c/0x7c
   init_thread_group_cache_map+0xd0/0x2d4
   smp_prepare_cpus+0x2bc/0x484
   kernel_init_freeable+0x168/0x3c4
   kernel_init+0x34/0x1ac

This happens because today we don't check for whether the properly is
present or not and directly pass the return value of
of_property_count_u32_elems(), to the allocator.

This went unnoticed because earlier kcalloc() caught the overflow due to
check_mul_overflow() check and returned NULL.
But since commit 0af298e62e5c ("treewide: refresh kmalloc_obj()
conversions") switched this call to kzalloc_objs(), size_mul() saturates
the size to SIZE_MAX instead and we now get a warning at boot.

Bail out early if the property is missing or empty. Follow the return
value as documented in kernel doc of parse_thread_groups() function.

Fixes: 790a1662d3a2 ("powerpc/smp: Parse ibm,thread-groups with multiple properties")
Reported-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 arch/powerpc/kernel/smp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 7a25eaa59e62..9a0f63e43821 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -824,6 +824,10 @@ static int parse_thread_groups(struct device_node *dn,
 	int i = 0;

 	count = of_property_count_u32_elems(dn, "ibm,thread-groups");
+	if (count < 0)
+		return count;
+	if (!count)
+		return -ENODATA;
 	thread_group_array = kzalloc_objs(u32, count);
 	if (!thread_group_array)
 		return -ENOMEM;
--
2.39.5