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locking/percpu-rwsem: Remove the embedded rwsem

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The filesystem freezer uses percpu-rwsem in a way that is effectively
write_non_owner() and achieves this with a few horrible hacks that
rely on the rwsem (!percpu) implementation.

When PREEMPT_RT replaces the rwsem implementation with a PI aware
variant this comes apart.

Remove the embedded rwsem and implement it using a waitqueue and an
atomic_t.

 - make readers_block an atomic, and use it, with the waitqueue
   for a blocking test-and-set write-side.

 - have the read-side wait for the 'lock' state to clear.

Have the waiters use FIFO queueing and mark them (reader/writer) with
a new WQ_FLAG. Use a custom wake_function to wake either a single
writer or all readers until a writer.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Waiman Long <longman@redhat.com>
Tested-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lkml.kernel.org/r/20200204092403.GB14879@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra
2019-10-30 20:30:41 +01:00
committed by Ingo Molnar
parent 75ff64572e
commit 7f26482a87
5 changed files with 126 additions and 74 deletions
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19
include/linux/percpu-rwsem.h
View File

@@ -3,18 +3,18 @@
#define _LINUX_PERCPU_RWSEM_H
#include <linux/atomic.h>
#include <linux/rwsem.h>
#include <linux/percpu.h>
#include <linux/rcuwait.h>
#include <linux/wait.h>
#include <linux/rcu_sync.h>
#include <linux/lockdep.h>
struct percpu_rw_semaphore {
struct rcu_sync rss;
unsigned int __percpu *read_count;
struct rw_semaphore rw_sem; /* slowpath */
struct rcuwait writer; /* blocked writer */
int readers_block;
struct rcuwait writer;
wait_queue_head_t waiters;
atomic_t block;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
@@ -31,8 +31,9 @@ static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
is_static struct percpu_rw_semaphore name = { \
.rss = __RCU_SYNC_INITIALIZER(name.rss), \
.read_count = &__percpu_rwsem_rc_##name, \
.rw_sem = __RWSEM_INITIALIZER(name.rw_sem), \
.writer = __RCUWAIT_INITIALIZER(name.writer), \
.waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters), \
.block = ATOMIC_INIT(0), \
__PERCPU_RWSEM_DEP_MAP_INIT(name) \
}
@@ -130,20 +131,12 @@ static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
bool read, unsigned long ip)
{
lock_release(&sem->dep_map, ip);
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
if (!read)
atomic_long_set(&sem->rw_sem.owner, RWSEM_OWNER_UNKNOWN);
#endif
}
static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
bool read, unsigned long ip)
{
lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
if (!read)
atomic_long_set(&sem->rw_sem.owner, (long)current);
#endif
}
#endif