path: root/kernel
diff options
authorEric W. Biederman <ebiederm@xmission.com>2019-09-14 07:33:34 -0500
committerIngo Molnar <mingo@kernel.org>2019-09-25 17:42:29 +0200
commit3fbd7ee285b2bbc6eebd15a3c8786d9776a402a8 (patch)
treea953a7cc7d724fe39e2c1bd2d218d3dd956c180f /kernel
parent42fd8baab31f53bed2952485fcf0e92f244c5e55 (diff)
tasks: Add a count of task RCU users
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>
Diffstat (limited to 'kernel')
2 files changed, 9 insertions, 5 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index 22ab6a4bdc51..3bcaec2ea3ba 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -182,6 +182,11 @@ static void delayed_put_task_struct(struct rcu_head *rhp)
+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 @@ repeat:
- call_rcu(&p->rcu, delayed_put_task_struct);
+ put_task_struct_rcu_user(p);
p = leader;
if (unlikely(zap_leader))
diff --git a/kernel/fork.c b/kernel/fork.c
index 1d1cd06edbc1..7eefe338d7a2 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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);
tsk->btrace_seq = 0;