From: Miaohe Lin <linmiaohe@huawei.com>
Date: Fri, 29 Apr 2022 06:16:18 +0000 (-0700)
Subject: mm: compaction: avoid possible NULL pointer dereference in kcompactd_cpu_online
X-Git-Tag: sched-urgent-2022-06-05~14^2~269
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=3109de308987ceae413ee015038d51e2a86c7806;p=users%2Fdwmw2%2Flinux.git

mm: compaction: avoid possible NULL pointer dereference in kcompactd_cpu_online

It's possible that kcompactd_run could fail to run kcompactd for a hot
added node and leave pgdat->kcompactd as NULL.  So pgdat->kcompactd should
be checked here to avoid possible NULL pointer dereference.

Link: https://lkml.kernel.org/r/20220418141253.24298-10-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Charan Teja Kalla <charante@codeaurora.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Pintu Kumar <pintu@codeaurora.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/compaction.c b/mm/compaction.c
index 562f274b2c512..82c54d70a978c 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -3052,7 +3052,8 @@ static int kcompactd_cpu_online(unsigned int cpu)
 
 		if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
 			/* One of our CPUs online: restore mask */
-			set_cpus_allowed_ptr(pgdat->kcompactd, mask);
+			if (pgdat->kcompactd)
+				set_cpus_allowed_ptr(pgdat->kcompactd, mask);
 	}
 	return 0;
 }