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tasks: Add a count of task RCU users

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Add a count of the number of RCU users (currently 1) of the task
struct so that we can later add the scheduler case and get rid of the
very subtle task_rcu_dereference(), and just use rcu_dereference().

As suggested by Oleg have the count overlap rcu_head so that no
additional space in task_struct is required.

Inspired-by: Linus Torvalds <torvalds@linux-foundation.org>
Inspired-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russell King - ARM Linux admin <linux@armlinux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/87woebdplt.fsf_-_@x220.int.ebiederm.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Eric W. Biederman 2019-09-14 07:33:34 -05:00 committed by Ingo Molnar
parent 42fd8baab3
commit 3fbd7ee285
4 changed files with 14 additions and 6 deletions
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5
include/linux/sched.h
View file

@ -1147,7 +1147,10 @@ struct task_struct {
struct tlbflush_unmap_batch tlb_ubc;
struct rcu_head rcu;
union {
refcount_t rcu_users;
struct rcu_head rcu;
};
/* Cache last used pipe for splice(): */
struct pipe_inode_info *splice_pipe;

1
include/linux/sched/task.h
View file

@ -120,6 +120,7 @@ static inline void put_task_struct(struct task_struct *t)
}
struct task_struct *task_rcu_dereference(struct task_struct **ptask);
void put_task_struct_rcu_user(struct task_struct *task);
#ifdef CONFIG_ARCH_WANTS_DYNAMIC_TASK_STRUCT
extern int arch_task_struct_size __read_mostly;

7
kernel/exit.c
View file

@ -182,6 +182,11 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
put_task_struct(tsk);
}
void put_task_struct_rcu_user(struct task_struct *task)
{
if (refcount_dec_and_test(&task->rcu_users))
call_rcu(&task->rcu, delayed_put_task_struct);
}
void release_task(struct task_struct *p)
{
@ -222,7 +227,7 @@ void release_task(struct task_struct *p)
write_unlock_irq(&tasklist_lock);
release_thread(p);
call_rcu(&p->rcu, delayed_put_task_struct);
put_task_struct_rcu_user(p);
p = leader;
if (unlikely(zap_leader))

7
kernel/fork.c
View file

@ -902,10 +902,9 @@ static struct task_struct *dup_task_struct(struct task_struct *orig, int node)
if (orig->cpus_ptr == &orig->cpus_mask)
tsk->cpus_ptr = &tsk->cpus_mask;
/*
* One for us, one for whoever does the "release_task()" (usually
* parent)
*/
/* One for the user space visible state that goes away when reaped. */
refcount_set(&tsk->rcu_users, 1);
/* One for the rcu users, and one for the scheduler */
refcount_set(&tsk->usage, 2);
#ifdef CONFIG_BLK_DEV_IO_TRACE
tsk->btrace_seq = 0;