Thread (63 messages) 63 messages, 6 authors, 2014-03-18
STALE4454d
Revisions (2)
  1. v2 [diff vs current]
  2. v3 current

[PATCH v3 36/52] zsmalloc: Fix CPU hotplug callback registration

From: Srivatsa S. Bhat <hidden>
Date: 2014-03-10 20:40:18
Also in: linux-arch, linux-mm, linux-pm, lkml
Subsystem: memory management, the rest, zsmalloc compressed slab memory allocator · Maintainers: Andrew Morton, Linus Torvalds, Minchan Kim, Sergey Senozhatsky

Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();


Fix the zsmalloc code by using this latter form of callback registration.

Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <redacted>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: linux-mm@kvack.org
Signed-off-by: Srivatsa S. Bhat <redacted>
---

 mm/zsmalloc.c |   17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index c03ca5e..36b4591 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -814,21 +814,32 @@ static void zs_exit(void)
 {
 	int cpu;
 
+	cpu_notifier_register_begin();
+
 	for_each_online_cpu(cpu)
 		zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
-	unregister_cpu_notifier(&zs_cpu_nb);
+	__unregister_cpu_notifier(&zs_cpu_nb);
+
+	cpu_notifier_register_done();
 }
 
 static int zs_init(void)
 {
 	int cpu, ret;
 
-	register_cpu_notifier(&zs_cpu_nb);
+	cpu_notifier_register_begin();
+
+	__register_cpu_notifier(&zs_cpu_nb);
 	for_each_online_cpu(cpu) {
 		ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
-		if (notifier_to_errno(ret))
+		if (notifier_to_errno(ret)) {
+			cpu_notifier_register_done();
 			goto fail;
+		}
 	}
+
+	cpu_notifier_register_done();
+
 	return 0;
 fail:
 	zs_exit();
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