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authorOleg Nesterov <oleg@tv-sign.ru>2008-04-29 04:00:29 -0400
committerLinus Torvalds <torvalds@linux-foundation.org>2008-04-29 11:06:11 -0400
commitd2ba7e2ae206e9ab24e8937d99d0d5513bfd08e5 (patch)
tree4cdd43bbf03885705fed5c80e982d19d397afaeb /kernel/cpu.c
parent1e35eaa2d86419470f3f3aed9acd85b8addff25c (diff)
simplify cpu_hotplug_begin()/put_online_cpus()
cpu_hotplug_begin() must be always called under cpu_add_remove_lock, this means that only one process can be cpu_hotplug.active_writer. So we don't need the cpu_hotplug.writer_queue, we can wake up the ->active_writer directly. Also, fix the comment. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: Dipankar Sarma <dipankar@in.ibm.com> Acked-by: Gautham R Shenoy <ego@in.ibm.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel/cpu.c')
-rw-r--r--kernel/cpu.c30
1 files changed, 10 insertions, 20 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index f8f9468d17d7..a98f6ab16ecd 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -33,17 +33,13 @@ static struct {
33 * an ongoing cpu hotplug operation. 33 * an ongoing cpu hotplug operation.
34 */ 34 */
35 int refcount; 35 int refcount;
36 wait_queue_head_t writer_queue;
37} cpu_hotplug; 36} cpu_hotplug;
38 37
39#define writer_exists() (cpu_hotplug.active_writer != NULL)
40
41void __init cpu_hotplug_init(void) 38void __init cpu_hotplug_init(void)
42{ 39{
43 cpu_hotplug.active_writer = NULL; 40 cpu_hotplug.active_writer = NULL;
44 mutex_init(&cpu_hotplug.lock); 41 mutex_init(&cpu_hotplug.lock);
45 cpu_hotplug.refcount = 0; 42 cpu_hotplug.refcount = 0;
46 init_waitqueue_head(&cpu_hotplug.writer_queue);
47} 43}
48 44
49#ifdef CONFIG_HOTPLUG_CPU 45#ifdef CONFIG_HOTPLUG_CPU
@@ -65,11 +61,8 @@ void put_online_cpus(void)
65 if (cpu_hotplug.active_writer == current) 61 if (cpu_hotplug.active_writer == current)
66 return; 62 return;
67 mutex_lock(&cpu_hotplug.lock); 63 mutex_lock(&cpu_hotplug.lock);
68 cpu_hotplug.refcount--; 64 if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
69 65 wake_up_process(cpu_hotplug.active_writer);
70 if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
71 wake_up(&cpu_hotplug.writer_queue);
72
73 mutex_unlock(&cpu_hotplug.lock); 66 mutex_unlock(&cpu_hotplug.lock);
74 67
75} 68}
@@ -98,8 +91,8 @@ void cpu_maps_update_done(void)
98 * Note that during a cpu-hotplug operation, the new readers, if any, 91 * Note that during a cpu-hotplug operation, the new readers, if any,
99 * will be blocked by the cpu_hotplug.lock 92 * will be blocked by the cpu_hotplug.lock
100 * 93 *
101 * Since cpu_maps_update_begin is always called after invoking 94 * Since cpu_hotplug_begin() is always called after invoking
102 * cpu_maps_update_begin, we can be sure that only one writer is active. 95 * cpu_maps_update_begin(), we can be sure that only one writer is active.
103 * 96 *
104 * Note that theoretically, there is a possibility of a livelock: 97 * Note that theoretically, there is a possibility of a livelock:
105 * - Refcount goes to zero, last reader wakes up the sleeping 98 * - Refcount goes to zero, last reader wakes up the sleeping
@@ -115,19 +108,16 @@ void cpu_maps_update_done(void)
115 */ 108 */
116static void cpu_hotplug_begin(void) 109static void cpu_hotplug_begin(void)
117{ 110{
118 DECLARE_WAITQUEUE(wait, current);
119
120 mutex_lock(&cpu_hotplug.lock);
121
122 cpu_hotplug.active_writer = current; 111 cpu_hotplug.active_writer = current;
123 add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait); 112
124 while (cpu_hotplug.refcount) { 113 for (;;) {
125 set_current_state(TASK_UNINTERRUPTIBLE); 114 mutex_lock(&cpu_hotplug.lock);
115 if (likely(!cpu_hotplug.refcount))
116 break;
117 __set_current_state(TASK_UNINTERRUPTIBLE);
126 mutex_unlock(&cpu_hotplug.lock); 118 mutex_unlock(&cpu_hotplug.lock);
127 schedule(); 119 schedule();
128 mutex_lock(&cpu_hotplug.lock);
129 } 120 }
130 remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
131} 121}
132 122
133static void cpu_hotplug_done(void) 123static void cpu_hotplug_done(void)