The patch titled simplify cpu_hotplug_begin()/put_online_cpus() has been removed from the -mm tree. Its filename was simplify-cpu_hotplug_begin-put_online_cpus.patch This patch was dropped because it was merged into mainline or a subsystem tree 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> Cc: 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 git-sched.patch kthread-add-a-missing-memory-barrier-to-kthread_stop.patch kthread-call-wake_up_process-without-the-lock-being-held.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 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 - To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html