From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>
Cc: linux-kernel@vger.kernel.org, john.p.donnelly@oracle.com,
"Hillf Danton" <hdanton@sina.com>,
"Mukesh Ojha" <quic_mojha@quicinc.com>,
"Ting11 Wang 王婷" <wangting11@xiaomi.com>,
"Waiman Long" <longman@redhat.com>
Subject: [PATCH v3 3/5] locking/rwsem: Change waiter->hanodff_set to a handoff_state enum
Date: Mon, 17 Oct 2022 17:13:54 -0400 [thread overview]
Message-ID: <20221017211356.333862-4-longman@redhat.com> (raw)
In-Reply-To: <20221017211356.333862-1-longman@redhat.com>
Change the boolean waiter->handoff_set to an enum type so that we can
have more states in some later patches. Also use READ_ONCE() outside
wait_lock critical sections for read and WRITE_ONCE() inside wait_lock
critical sections for write for proper synchronization. There is no
functional change.
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/rwsem.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index c68d76fc8c68..a8bfc905637a 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -338,12 +338,17 @@ enum rwsem_waiter_type {
RWSEM_WAITING_FOR_READ
};
+enum rwsem_handoff_state {
+ HANDOFF_NONE = 0,
+ HANDOFF_REQUESTED,
+};
+
struct rwsem_waiter {
struct list_head list;
struct task_struct *task;
enum rwsem_waiter_type type;
+ enum rwsem_handoff_state handoff_state;
unsigned long timeout;
- bool handoff_set;
};
#define rwsem_first_waiter(sem) \
list_first_entry(&sem->wait_list, struct rwsem_waiter, list)
@@ -470,7 +475,7 @@ static void rwsem_mark_wake(struct rw_semaphore *sem,
adjustment -= RWSEM_FLAG_HANDOFF;
lockevent_inc(rwsem_rlock_handoff);
}
- waiter->handoff_set = true;
+ WRITE_ONCE(waiter->handoff_state, HANDOFF_REQUESTED);
}
atomic_long_add(-adjustment, &sem->count);
@@ -622,7 +627,7 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
* waiter is the one that set it. Otherwisee, we
* still try to acquire the rwsem.
*/
- if (first->handoff_set && (waiter != first))
+ if (first->handoff_state && (waiter != first))
return false;
}
@@ -650,11 +655,11 @@ static inline bool rwsem_try_write_lock(struct rw_semaphore *sem,
/*
* We have either acquired the lock with handoff bit cleared or set
- * the handoff bit. Only the first waiter can have its handoff_set
+ * the handoff bit. Only the first waiter can have its handoff_state
* set here to enable optimistic spinning in slowpath loop.
*/
if (new & RWSEM_FLAG_HANDOFF) {
- first->handoff_set = true;
+ WRITE_ONCE(first->handoff_state, HANDOFF_REQUESTED);
lockevent_inc(rwsem_wlock_handoff);
return false;
}
@@ -1043,7 +1048,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, long count, unsigned int stat
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_READ;
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
- waiter.handoff_set = false;
+ waiter.handoff_state = HANDOFF_NONE;
raw_spin_lock_irq(&sem->wait_lock);
if (list_empty(&sem->wait_list)) {
@@ -1131,7 +1136,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
waiter.task = current;
waiter.type = RWSEM_WAITING_FOR_WRITE;
waiter.timeout = jiffies + RWSEM_WAIT_TIMEOUT;
- waiter.handoff_set = false;
+ waiter.handoff_state = HANDOFF_NONE;
raw_spin_lock_irq(&sem->wait_lock);
rwsem_add_waiter(sem, &waiter);
@@ -1176,7 +1181,7 @@ rwsem_down_write_slowpath(struct rw_semaphore *sem, int state)
* In this case, we attempt to acquire the lock again
* without sleeping.
*/
- if (waiter.handoff_set) {
+ if (READ_ONCE(waiter.handoff_state)) {
enum owner_state owner_state;
preempt_disable();
--
2.31.1
next prev parent reply other threads:[~2022-10-17 21:14 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-17 21:13 [PATCH v3 0/5] lockinig/rwsem: Fix rwsem bugs & enable true lock handoff Waiman Long
2022-10-17 21:13 ` [PATCH v3 1/5] locking/rwsem: Prevent non-first waiter from spinning in down_write() slowpath Waiman Long
2022-10-24 13:17 ` Peter Zijlstra
2022-10-24 13:50 ` Waiman Long
2022-10-17 21:13 ` [PATCH v3 2/5] locking/rwsem: Limit # of null owner retries for handoff writer Waiman Long
2022-10-24 13:31 ` Peter Zijlstra
2022-10-24 15:55 ` Waiman Long
2022-10-25 11:22 ` Peter Zijlstra
2022-10-25 11:48 ` Peter Zijlstra
2022-10-25 19:55 ` Waiman Long
2022-10-25 20:14 ` Peter Zijlstra
2022-10-26 1:44 ` Waiman Long
[not found] ` <20221025145843.2953-1-hdanton@sina.com>
2022-10-25 19:00 ` Waiman Long
2022-10-17 21:13 ` Waiman Long [this message]
2022-10-17 21:13 ` [PATCH v3 4/5] locking/rwsem: Enable direct rwsem lock handoff Waiman Long
2022-10-17 21:13 ` [PATCH v3 5/5] locking/rwsem: Update handoff lock events tracking Waiman Long
[not found] ` <20221018111424.1007-1-hdanton@sina.com>
2022-10-18 14:13 ` [PATCH v3 4/5] locking/rwsem: Enable direct rwsem lock handoff Mukesh Ojha
2022-10-18 17:37 ` Waiman Long
[not found] ` <20221018235138.1088-1-hdanton@sina.com>
2022-10-19 0:39 ` Waiman Long
[not found] ` <20221019022934.1166-1-hdanton@sina.com>
2022-10-19 2:49 ` Waiman Long
[not found] ` <20221019070559.1220-1-hdanton@sina.com>
2022-10-19 15:02 ` Waiman Long
2022-10-24 16:18 ` Waiman Long
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