From: Waiman Long <longman@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
huang ying <huang.ying.caritas@gmail.com>,
Waiman Long <longman@redhat.com>
Subject: [PATCH v8 19/19] locking/rwsem: Disable preemption in down_read*() if owner in count
Date: Mon, 20 May 2019 16:59:18 -0400 [thread overview]
Message-ID: <20190520205918.22251-20-longman@redhat.com> (raw)
In-Reply-To: <20190520205918.22251-1-longman@redhat.com>
It is very unlikely that successive preemption at the middle of
down_read's inc-check-dec sequence will cause the reader count to
overflow, For absolute correctness, however, we still need to prevent
that possibility from happening. So preemption will be disabled during
the down_read*() call.
For PREEMPT=n kernels, there isn't much overhead in doing that.
For PREEMPT=y kernels, there will be some additional cost. RT kernels
have their own rwsem code, so it will not be a problem for them.
If MERGE_OWNER_INTO_COUNT isn't defined, we don't need to worry about
reader count overflow and so we don't need to disable preemption.
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/locking/rwsem.c | 38 ++++++++++++++++++++++++++++++++++----
1 file changed, 34 insertions(+), 4 deletions(-)
diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index 29f0e0e5b62e..cede2f99220b 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -356,6 +356,24 @@ static inline void rwsem_set_nonspinnable(struct rw_semaphore *sem)
}
#ifdef MERGE_OWNER_INTO_COUNT
+/*
+ * It is very unlikely that successive preemption at the middle of
+ * down_read's inc-check-dec sequence will cause the reader count to
+ * overflow, For absolute correctness, we still need to prevent
+ * that possibility from happening. So preemption will be disabled
+ * during the down_read*() call.
+ *
+ * For PREEMPT=n kernels, there isn't much overhead in doing that.
+ * For PREEMPT=y kernels, there will be some additional cost.
+ *
+ * If MERGE_OWNER_INTO_COUNT isn't defined, we don't need to worry
+ * about reader count overflow and so we don't need to disable
+ * preemption.
+ */
+#define rwsem_preempt_disable() preempt_disable()
+#define rwsem_preempt_enable() preempt_enable()
+#define rwsem_schedule_preempt_disabled() schedule_preempt_disabled()
+
/*
* Get the owner value from count to have early access to the task structure.
*/
@@ -420,6 +438,10 @@ late_initcall(rwsem_show_count_status);
#else /* !MERGE_OWNER_INTO_COUNT */
+#define rwsem_preempt_disable()
+#define rwsem_preempt_enable()
+#define rwsem_schedule_preempt_disabled() schedule()
+
/*
* Return just the real task structure pointer of the owner
*/
@@ -1247,7 +1269,7 @@ rwsem_down_read_slowpath(struct rw_semaphore *sem, int state, long adjustment)
raw_spin_unlock_irq(&sem->wait_lock);
break;
}
- schedule();
+ rwsem_schedule_preempt_disabled();
lockevent_inc(rwsem_sleep_reader);
}
@@ -1472,28 +1494,36 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
*/
inline void __down_read(struct rw_semaphore *sem)
{
- long tmp, adjustment = rwsem_read_trylock(sem, &tmp);
+ long tmp, adjustment;
+ rwsem_preempt_disable();
+ adjustment = rwsem_read_trylock(sem, &tmp);
if (unlikely(tmp & RWSEM_READ_FAILED_MASK)) {
rwsem_down_read_slowpath(sem, TASK_UNINTERRUPTIBLE, adjustment);
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
}
+ rwsem_preempt_enable();
}
static inline int __down_read_killable(struct rw_semaphore *sem)
{
- long tmp, adjustment = rwsem_read_trylock(sem, &tmp);
+ long tmp, adjustment;
+ rwsem_preempt_disable();
+ adjustment = rwsem_read_trylock(sem, &tmp);
if (unlikely(tmp & RWSEM_READ_FAILED_MASK)) {
if (IS_ERR(rwsem_down_read_slowpath(sem, TASK_KILLABLE,
- adjustment)))
+ adjustment))) {
+ rwsem_preempt_enable();
return -EINTR;
+ }
DEBUG_RWSEMS_WARN_ON(!is_rwsem_reader_owned(sem), sem);
} else {
rwsem_set_reader_owned(sem);
}
+ rwsem_preempt_enable();
return 0;
}
--
2.18.1
prev parent reply other threads:[~2019-05-20 21:00 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 20:58 [PATCH v8 00/19] locking/rwsem: Rwsem rearchitecture part 2 Waiman Long
2019-05-20 20:59 ` [PATCH v8 01/19] locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER Waiman Long
2019-06-17 14:23 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 02/19] locking/rwsem: Remove rwsem_wake() wakeup optimization Waiman Long
2019-06-17 14:24 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 03/19] locking/rwsem: Implement a new locking scheme Waiman Long
2019-06-17 14:24 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 04/19] locking/rwsem: Merge rwsem.h and rwsem-xadd.c into rwsem.c Waiman Long
2019-06-17 14:25 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 05/19] locking/rwsem: Code cleanup after files merging Waiman Long
2019-06-17 14:26 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 06/19] locking/rwsem: Make rwsem_spin_on_owner() return owner state Waiman Long
2019-06-17 14:27 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 07/19] locking/rwsem: Implement lock handoff to prevent lock starvation Waiman Long
2019-06-04 3:03 ` Yuyang Du
2019-06-04 3:26 ` Yuyang Du
2019-06-04 9:12 ` Boqun Feng
2019-06-04 16:00 ` Waiman Long
2019-06-05 7:48 ` Yuyang Du
2019-06-04 13:21 ` Waiman Long
2019-06-17 14:27 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 08/19] locking/rwsem: Always release wait_lock before waking up tasks Waiman Long
2019-06-17 14:28 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 09/19] locking/rwsem: More optimal RT task handling of null owner Waiman Long
2019-06-17 14:29 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 10/19] locking/rwsem: Wake up almost all readers in wait queue Waiman Long
2019-06-17 14:29 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 11/19] locking/rwsem: Clarify usage of owner's nonspinaable bit Waiman Long
2019-06-17 14:30 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 12/19] locking/rwsem: Enable readers spinning on writer Waiman Long
2019-06-17 14:31 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 13/19] locking/rwsem: Make rwsem->owner an atomic_long_t Waiman Long
2019-06-04 8:52 ` Peter Zijlstra
2019-06-04 15:44 ` Waiman Long
2019-06-17 14:32 ` [tip:locking/core] " tip-bot for Waiman Long
2019-07-19 18:45 ` [PATCH v8 13/19] " Luis Henriques
2019-07-19 19:32 ` Waiman Long
2019-07-19 19:45 ` Luis Henriques
2019-07-19 20:14 ` Waiman Long
2019-07-19 19:51 ` Linus Torvalds
2019-07-20 8:41 ` Luis Henriques
2019-07-20 9:32 ` Luis Henriques
2019-07-20 9:45 ` Luis Henriques
2019-07-20 11:10 ` Peter Zijlstra
2019-07-20 15:04 ` Waiman Long
2019-07-21 20:49 ` Luis Henriques
2019-07-23 2:57 ` Waiman Long
2019-07-25 15:59 ` [tip:locking/core] locking/rwsem: Don't call owner_on_cpu() on read-owner tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 14/19] locking/rwsem: Enable time-based spinning on reader-owned rwsem Waiman Long
2019-06-04 9:03 ` Peter Zijlstra
2019-06-04 16:54 ` Waiman Long
2019-06-17 14:32 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 15/19] locking/rwsem: Adaptive disabling of reader optimistic spinning Waiman Long
2019-06-04 9:10 ` Peter Zijlstra
2019-06-04 17:28 ` Waiman Long
2019-06-04 9:14 ` Peter Zijlstra
2019-06-04 17:29 ` Waiman Long
2019-06-04 9:20 ` Peter Zijlstra
2019-06-04 17:30 ` Waiman Long
2019-06-04 17:38 ` Peter Zijlstra
2019-06-04 18:04 ` Waiman Long
2019-06-04 18:14 ` Peter Zijlstra
2019-06-04 18:21 ` Waiman Long
2019-06-05 18:13 ` Waiman Long
2019-06-05 20:19 ` Peter Zijlstra
2019-06-05 20:52 ` Linus Torvalds
2019-06-06 8:03 ` Peter Zijlstra
2019-06-06 8:11 ` Peter Zijlstra
2019-06-04 10:58 ` Peter Zijlstra
2019-06-17 14:33 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 16/19] locking/rwsem: Guard against making count negative Waiman Long
2019-06-11 13:11 ` Peter Zijlstra
2019-06-11 13:27 ` Peter Zijlstra
2019-06-11 13:13 ` Peter Zijlstra
2019-06-17 14:34 ` [tip:locking/core] " tip-bot for Waiman Long
2019-05-20 20:59 ` [PATCH v8 17/19] locking/rwsem: Merge owner into count on x86-64 Waiman Long
2019-06-04 9:45 ` Peter Zijlstra
2019-06-04 15:47 ` Waiman Long
2019-06-04 17:02 ` Peter Zijlstra
2019-06-04 17:06 ` Waiman Long
2019-06-04 17:18 ` Peter Zijlstra
2019-05-20 20:59 ` [PATCH v8 18/19] locking/rwsem: Remove redundant computation of writer lock word Waiman Long
2019-05-20 20:59 ` Waiman Long [this message]
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