The patch titled
simplify cpu_hotplug_begin()/put_online_cpus()
has been added to the -mm tree. Its filename is
simplify-cpu_hotplug_begin-put_online_cpus.patch
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See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: simplify cpu_hotplug_begin()/put_online_cpus()
From: Oleg Nesterov <oleg@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Dipankar Sarma <dipankar@xxxxxxxxxx>
Acked-by: Gautham R Shenoy <ego@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Srivatsa Vaddagiri <vatsa@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/cpu.c | 30 ++++++++++--------------------
1 file changed, 10 insertions(+), 20 deletions(-)
diff -puN kernel/cpu.c~simplify-cpu_hotplug_begin-put_online_cpus kernel/cpu.c
--- a/kernel/cpu.c~simplify-cpu_hotplug_begin-put_online_cpus
+++ a/kernel/cpu.c
@@ -33,17 +33,13 @@ static struct {
* an ongoing cpu hotplug operation.
*/
int refcount;
- wait_queue_head_t writer_queue;
} cpu_hotplug;
-#define writer_exists() (cpu_hotplug.active_writer != NULL)
-
void __init cpu_hotplug_init(void)
{
cpu_hotplug.active_writer = NULL;
mutex_init(&cpu_hotplug.lock);
cpu_hotplug.refcount = 0;
- init_waitqueue_head(&cpu_hotplug.writer_queue);
}
#ifdef CONFIG_HOTPLUG_CPU
@@ -65,11 +61,8 @@ void put_online_cpus(void)
if (cpu_hotplug.active_writer == current)
return;
mutex_lock(&cpu_hotplug.lock);
- cpu_hotplug.refcount--;
-
- if (unlikely(writer_exists()) && !cpu_hotplug.refcount)
- wake_up(&cpu_hotplug.writer_queue);
-
+ if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
+ wake_up_process(cpu_hotplug.active_writer);
mutex_unlock(&cpu_hotplug.lock);
}
@@ -98,8 +91,8 @@ void cpu_maps_update_done(void)
* Note that during a cpu-hotplug operation, the new readers, if any,
* will be blocked by the cpu_hotplug.lock
*
- * Since cpu_maps_update_begin is always called after invoking
- * cpu_maps_update_begin, we can be sure that only one writer is active.
+ * Since cpu_hotplug_begin() is always called after invoking
+ * cpu_maps_update_begin(), we can be sure that only one writer is active.
*
* Note that theoretically, there is a possibility of a livelock:
* - Refcount goes to zero, last reader wakes up the sleeping
@@ -115,19 +108,16 @@ void cpu_maps_update_done(void)
*/
static void cpu_hotplug_begin(void)
{
- DECLARE_WAITQUEUE(wait, current);
-
- mutex_lock(&cpu_hotplug.lock);
-
cpu_hotplug.active_writer = current;
- add_wait_queue_exclusive(&cpu_hotplug.writer_queue, &wait);
- while (cpu_hotplug.refcount) {
- set_current_state(TASK_UNINTERRUPTIBLE);
+
+ for (;;) {
+ mutex_lock(&cpu_hotplug.lock);
+ if (likely(!cpu_hotplug.refcount))
+ break;
+ __set_current_state(TASK_UNINTERRUPTIBLE);
mutex_unlock(&cpu_hotplug.lock);
schedule();
- mutex_lock(&cpu_hotplug.lock);
}
- remove_wait_queue_locked(&cpu_hotplug.writer_queue, &wait);
}
static void cpu_hotplug_done(void)
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
kthread-add-a-missing-memory-barrier-to-kthread_stop.patch
kthread-call-wake_up_process-without-the-lock-being-held.patch
documentation-atomic_add_unless-doesnt-imply-mb-on-failure-fix.patch
mmap_region-cleanup-the-final-vma_merge-related-code.patch
remove-unused-variable-from-send_signal.patch
turn-legacy_queue-macro-into-static-inline-function.patch
consolidate-checking-for-ignored-legacy-signals.patch
consolidate-checking-for-ignored-legacy-signals-simplify.patch
signals-do_signal_stop-use-signal_group_exit.patch
signals-do_group_exit-use-signal_group_exit-more-consistently.patch
lock_task_sighand-add-rcu-lock-unlock.patch
k_getrusage-dont-take-rcu_read_lock.patch
do_task_stat-dont-take-rcu_read_lock.patch
workqueues-shrink-cpu_populated_map-when-cpu-dies.patch
workqueues-shrink-cpu_populated_map-when-cpu-dies-fix.patch
cleanup_workqueue_thread-remove-the-unneeded-cpu-parameter.patch
simplify-cpu_hotplug_begin-put_online_cpus.patch
timers-simplify-lockdep-stuff.patch
hrtimers-simplify-lockdep-stuff.patch
kill-double_spin_lock.patch
redo-locking-of-tty-pgrp.patch
procfs-task-exe-symlink.patch
procfs-task-exe-symlink-fix.patch
procfs-task-exe-symlink-fix-2.patch
free_pidmap-turn-it-into-free_pidmapstruct-upid.patch
put_pid-make-sure-we-dont-free-the-live-pid.patch
-
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