[PATCH 1/1] sched/topology: fix memleak in __sdt_alloc()

[shuwang]

From: Shu Wang <shuwang@xxxxxxxxxx>

Found this issue by kmemleak. the sg and sgc from __sdt_alloc()
might be leaked as each domain holds many groups' ref. And in
destroy_sched_domain(), it only declined the first group ref.

Online and offline a cpu can trigger this leak, and cause OOM.
reproducer for my 6 cpus machine:
while true
do
    echo 0 > /sys/devices/system/cpu/cpu5/online;
    echo 1 > /sys/devices/system/cpu/cpu5/online;
done

unreferenced object 0xffff88007d772a80 (size 64):
  comm "cpuhp/5", pid 39, jiffies 4294719962 (age 35.251s)
  hex dump (first 32 bytes):
    c0 22 77 7d 00 88 ff ff 02 00 00 00 01 00 00 00  ."w}............
    40 2a 77 7d 00 88 ff ff 00 00 00 00 00 00 00 00  @*w}............
  backtrace:
    [<ffffffff8176525a>] kmemleak_alloc+0x4a/0xa0
    [<ffffffff8121efe1>] __kmalloc_node+0xf1/0x280
    [<ffffffff810d94a8>] build_sched_domains+0x1e8/0xf20
    [<ffffffff810da674>] partition_sched_domains+0x304/0x360
    [<ffffffff81139557>] cpuset_update_active_cpus+0x17/0x40
    [<ffffffff810bdb2e>] sched_cpu_activate+0xae/0xc0
    [<ffffffff810900e0>] cpuhp_invoke_callback+0x90/0x400
    [<ffffffff81090597>] cpuhp_up_callbacks+0x37/0xb0
    [<ffffffff81090887>] cpuhp_thread_fun+0xd7/0xf0
    [<ffffffff810b37e0>] smpboot_thread_fn+0x110/0x160
    [<ffffffff810af5d9>] kthread+0x109/0x140
    [<ffffffff81770e45>] ret_from_fork+0x25/0x30
    [<ffffffffffffffff>] 0xffffffffffffffff
unreferenced object 0xffff88007d772a40 (size 64):
  comm "cpuhp/5", pid 39, jiffies 4294719962 (age 35.251s)
  hex dump (first 32 bytes):
    03 00 00 00 00 00 00 00 00 04 00 00 00 00 00 00  ................
    00 04 00 00 00 00 00 00 4f 3c fc ff 00 00 00 00  ........O<......
  backtrace:
    [<ffffffff8176525a>] kmemleak_alloc+0x4a/0xa0
    [<ffffffff8121efe1>] __kmalloc_node+0xf1/0x280
    [<ffffffff810da16d>] build_sched_domains+0xead/0xf20
    [<ffffffff810da674>] partition_sched_domains+0x304/0x360
    [<ffffffff81139557>] cpuset_update_active_cpus+0x17/0x40
    [<ffffffff810bdb2e>] sched_cpu_activate+0xae/0xc0
    [<ffffffff810900e0>] cpuhp_invoke_callback+0x90/0x400
    [<ffffffff81090597>] cpuhp_up_callbacks+0x37/0xb0
    [<ffffffff81090887>] cpuhp_thread_fun+0xd7/0xf0
    [<ffffffff810b37e0>] smpboot_thread_fn+0x110/0x160
    [<ffffffff810af5d9>] kthread+0x109/0x140
    [<ffffffff81770e45>] ret_from_fork+0x25/0x30
    [<ffffffffffffffff>] 0xffffffffffffffff

Reported-by: Chunyu Hu <chuhu@xxxxxxxxxx>
Signed-off-by: Chunyu Hu <chuhu@xxxxxxxxxx>
Signed-off-by: Shu Wang <shuwang@xxxxxxxxxx>
---
 kernel/sched/topology.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 79895ae..35c3c4d 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -337,7 +337,8 @@ static void free_sched_groups(struct sched_group *sg, int free_sgc)
 		if (free_sgc && atomic_dec_and_test(&sg->sgc->ref))
 			kfree(sg->sgc);
 
-		kfree(sg);
+		if (atomic_dec_and_test(&sg->ref))
+			kfree(sg);
 		sg = tmp;
 	} while (sg != first);
 }
@@ -345,15 +346,11 @@ static void free_sched_groups(struct sched_group *sg, int free_sgc)
 static void destroy_sched_domain(struct sched_domain *sd)
 {
 	/*
-	 * If its an overlapping domain it has private groups, iterate and
-	 * nuke them all.
+	 * A sched domain has many groups' reference, and an overlapping
+	 * domain has private groups, iterate and nuck them all.
 	 */
-	if (sd->flags & SD_OVERLAP) {
-		free_sched_groups(sd->groups, 1);
-	} else if (atomic_dec_and_test(&sd->groups->ref)) {
-		kfree(sd->groups->sgc);
-		kfree(sd->groups);
-	}
+	free_sched_groups(sd->groups, 1);
+
 	if (sd->shared && atomic_dec_and_test(&sd->shared->ref))
 		kfree(sd->shared);
 	kfree(sd);
@@ -670,6 +667,7 @@ build_group_from_child_sched_domain(struct sched_domain *sd, int cpu)
 	else
 		cpumask_copy(sg_span, sched_domain_span(sd));
 
+	atomic_inc(&sg->ref);
 	return sg;
 }
 
-- 
2.5.0