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author | Paul E. McKenney <paulmck@us.ibm.com> | 2006-01-08 09:01:35 (GMT) |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-01-09 04:13:40 (GMT) |
commit | 4369ef3c3e9d3bd9b879580678778f558d481e90 (patch) | |
tree | 32b443b32c6de858c419f75dad07c46028359afe /drivers | |
parent | eafbaa94691f6a1fa67c3b076caa3ce4e2920100 (diff) | |
download | linux-4369ef3c3e9d3bd9b879580678778f558d481e90.tar.xz |
[PATCH] Make RCU task_struct safe for oprofile
Applying RCU to the task structure broke oprofile, because
free_task_notify() can now be called from softirq. This means that the
task_mortuary lock must be acquired with irq disabled in order to avoid
intermittent self-deadlock. Since irq is now disabled, the critical
section within process_task_mortuary() has been restructured to be O(1) in
order to maximize scalability and minimize realtime latency degradation.
Kudos to Wu Fengguang for finding this problem!
CC: Wu Fengguang <wfg@mail.ustc.edu.cn>
Cc: Philippe Elie <phil.el@wanadoo.fr>
Cc: John Levon <levon@movementarian.org>
Signed-off-by: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'drivers')
-rw-r--r-- | drivers/oprofile/buffer_sync.c | 30 |
1 files changed, 15 insertions, 15 deletions
diff --git a/drivers/oprofile/buffer_sync.c b/drivers/oprofile/buffer_sync.c index 531b073..b2e8e49 100644 --- a/drivers/oprofile/buffer_sync.c +++ b/drivers/oprofile/buffer_sync.c @@ -43,13 +43,16 @@ static void process_task_mortuary(void); * list for processing. Only after two full buffer syncs * does the task eventually get freed, because by then * we are sure we will not reference it again. + * Can be invoked from softirq via RCU callback due to + * call_rcu() of the task struct, hence the _irqsave. */ static int task_free_notify(struct notifier_block * self, unsigned long val, void * data) { + unsigned long flags; struct task_struct * task = data; - spin_lock(&task_mortuary); + spin_lock_irqsave(&task_mortuary, flags); list_add(&task->tasks, &dying_tasks); - spin_unlock(&task_mortuary); + spin_unlock_irqrestore(&task_mortuary, flags); return NOTIFY_OK; } @@ -431,25 +434,22 @@ static void increment_tail(struct oprofile_cpu_buffer * b) */ static void process_task_mortuary(void) { - struct list_head * pos; - struct list_head * pos2; + unsigned long flags; + LIST_HEAD(local_dead_tasks); struct task_struct * task; + struct task_struct * ttask; - spin_lock(&task_mortuary); + spin_lock_irqsave(&task_mortuary, flags); - list_for_each_safe(pos, pos2, &dead_tasks) { - task = list_entry(pos, struct task_struct, tasks); - list_del(&task->tasks); - free_task(task); - } + list_splice_init(&dead_tasks, &local_dead_tasks); + list_splice_init(&dying_tasks, &dead_tasks); - list_for_each_safe(pos, pos2, &dying_tasks) { - task = list_entry(pos, struct task_struct, tasks); + spin_unlock_irqrestore(&task_mortuary, flags); + + list_for_each_entry_safe(task, ttask, &local_dead_tasks, tasks) { list_del(&task->tasks); - list_add_tail(&task->tasks, &dead_tasks); + free_task(task); } - - spin_unlock(&task_mortuary); } |