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rcu: Make TASKS_RCU handle tasks that are almost done exiting

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Once a task has passed exit_notify() in the do_exit() code path, it
is no longer on the task lists, and is therefore no longer visible
to rcu_tasks_kthread().  This means that an almost-exited task might
be preempted while within a trampoline, and this task won't be waited
on by rcu_tasks_kthread().  This commit fixes this bug by adding an
srcu_struct.  An exiting task does srcu_read_lock() just before calling
exit_notify(), and does the corresponding srcu_read_unlock() after
doing the final preempt_disable().  This means that rcu_tasks_kthread()
can do synchronize_srcu() to wait for all mostly-exited tasks to reach
their final preempt_disable() region, and then use synchronize_sched()
to wait for those tasks to finish exiting.

Reported-by: Oleg Nesterov <oleg@redhat.com>
Suggested-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2014-08-04 06:10:23 -07:00
parent 53c6d4edf8
commit 3f95aa81d2
3 changed files with 27 additions and 0 deletions
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3
include/linux/rcupdate.h
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@@ -321,6 +321,8 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
* macro rather than an inline function to avoid #include hell.
*/
#ifdef CONFIG_TASKS_RCU
#define TASKS_RCU(x) x
extern struct srcu_struct tasks_rcu_exit_srcu;
#define rcu_note_voluntary_context_switch(t) \
do { \
preempt_disable(); /* Exclude synchronize_sched(); */ \
@@ -329,6 +331,7 @@ static inline void rcu_user_hooks_switch(struct task_struct *prev,
preempt_enable(); \
} while (0)
#else /* #ifdef CONFIG_TASKS_RCU */
#define TASKS_RCU(x) do { } while (0)
#define rcu_note_voluntary_context_switch(t) do { } while (0)
#endif /* #else #ifdef CONFIG_TASKS_RCU */