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Subject[tip:locking/core] locking/rwsem: Simplify the is-owner-spinnable checks
Commit-ID:  1b22fc609cecd1b16c4a015e1a6b3c9717484e3a
Gitweb: https://git.kernel.org/tip/1b22fc609cecd1b16c4a015e1a6b3c9717484e3a
Author: Oleg Nesterov <oleg@redhat.com>
AuthorDate: Fri, 18 May 2018 18:55:35 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 25 May 2018 08:11:47 +0200

locking/rwsem: Simplify the is-owner-spinnable checks

Add the trivial owner_on_cpu() helper for rwsem_can_spin_on_owner() and
rwsem_spin_on_owner(), it also allows to make rwsem_can_spin_on_owner()
a bit more clear.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Waiman Long <longman@redhat.com>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Theodore Y. Ts'o <tytso@mit.edu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20180518165534.GA22348@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/locking/rwsem-xadd.c | 25 +++++++++++++------------
1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a90336779375..3064c50e181e 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -347,6 +347,15 @@ static inline bool rwsem_try_write_lock_unqueued(struct rw_semaphore *sem)
}
}

+static inline bool owner_on_cpu(struct task_struct *owner)
+{
+ /*
+ * As lock holder preemption issue, we both skip spinning if
+ * task is not on cpu or its cpu is preempted
+ */
+ return owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
+}
+
static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)
{
struct task_struct *owner;
@@ -359,17 +368,10 @@ static inline bool rwsem_can_spin_on_owner(struct rw_semaphore *sem)

rcu_read_lock();
owner = READ_ONCE(sem->owner);
- if (!owner || !is_rwsem_owner_spinnable(owner)) {
- ret = !owner; /* !owner is spinnable */
- goto done;
+ if (owner) {
+ ret = is_rwsem_owner_spinnable(owner) &&
+ owner_on_cpu(owner);
}
-
- /*
- * As lock holder preemption issue, we both skip spinning if task is not
- * on cpu or its cpu is preempted
- */
- ret = owner->on_cpu && !vcpu_is_preempted(task_cpu(owner));
-done:
rcu_read_unlock();
return ret;
}
@@ -398,8 +400,7 @@ static noinline bool rwsem_spin_on_owner(struct rw_semaphore *sem)
* abort spinning when need_resched or owner is not running or
* owner's cpu is preempted.
*/
- if (!owner->on_cpu || need_resched() ||
- vcpu_is_preempted(task_cpu(owner))) {
+ if (need_resched() || !owner_on_cpu(owner)) {
rcu_read_unlock();
return false;
}
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