The following commit has been merged into the sched/urgent branch of tip: Commit-ID: 3fbd7ee285b2bbc6eebd15a3c8786d9776a402a8 Gitweb: https://git.kernel.org/tip/3fbd7ee285b2bbc6eebd15a3c8786d9776a402a8 Author: Eric W. Biederman <ebied...@xmission.com> AuthorDate: Sat, 14 Sep 2019 07:33:34 -05:00 Committer: Ingo Molnar <mi...@kernel.org> CommitterDate: Wed, 25 Sep 2019 17:42:29 +02:00
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 <torva...@linux-foundation.org> Inspired-by: Oleg Nesterov <o...@redhat.com> Signed-off-by: Eric W. Biederman <ebied...@xmission.com> Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org> Cc: Chris Metcalf <cmetc...@ezchip.com> Cc: Christoph Lameter <c...@linux.com> Cc: Davidlohr Bueso <d...@stgolabs.net> Cc: Kirill Tkhai <tk...@yandex.ru> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Mike Galbraith <efa...@gmx.de> Cc: Paul E. McKenney <paul...@kernel.org> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Russell King - ARM Linux admin <li...@armlinux.org.uk> Cc: Thomas Gleixner <t...@linutronix.de> Link: https://lkml.kernel.org/r/87woebdplt.fsf...@x220.int.ebiederm.org Signed-off-by: Ingo Molnar <mi...@kernel.org> --- include/linux/sched.h | 5 ++++- include/linux/sched/task.h | 1 + kernel/exit.c | 7 ++++++- kernel/fork.c | 7 +++---- 4 files changed, 14 insertions(+), 6 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index e2e9196..8e43e54 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -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; diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index 3d90ed8..153a683 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -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; diff --git a/kernel/exit.c b/kernel/exit.c index 22ab6a4..3bcaec2 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -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 @@ repeat: 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)) diff --git a/kernel/fork.c b/kernel/fork.c index 1d1cd06..7eefe33 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); #ifdef CONFIG_BLK_DEV_IO_TRACE tsk->btrace_seq = 0;
