locking/percpu-rwsem: Remove preempt_disable variants

Effective revert commit:

  87709e28 ("fs/locks: Use percpu_down_read_preempt_disable()")

This is causing major pain for PREEMPT_RT.

Sebastian did a lot of lockperf runs on 2 and 4 node machines with all
preemption modes (PREEMPT=n should be an obvious NOP for this patch
and thus serves as a good control) and no results showed significance
over 2-sigma (the PREEMPT=n results were almost empty at 1-sigma).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs/locks.c

@@ -1058,7 +1058,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request)
 			return -ENOMEM;
 	}
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	if (request->fl_flags & FL_ACCESS)
 		goto find_conflict;
@@ -1100,7 +1100,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request)
 
 out:
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 	if (new_fl)
 		locks_free_lock(new_fl);
 	locks_dispose_list(&dispose);
@@ -1138,7 +1138,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 		new_fl2 = locks_alloc_lock();
 	}
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	/*
 	 * New lock request. Walk all POSIX locks and look for conflicts. If
@@ -1312,7 +1312,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
 	}
  out:
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 	/*
 	 * Free any unused locks.
 	 */
@@ -1584,7 +1584,7 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
 		return error;
 	}
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 
 	time_out_leases(inode, &dispose);
@@ -1636,13 +1636,13 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
 	locks_insert_block(fl, new_fl, leases_conflict);
 	trace_break_lease_block(inode, new_fl);
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 
 	locks_dispose_list(&dispose);
 	error = wait_event_interruptible_timeout(new_fl->fl_wait,
 						!new_fl->fl_blocker, break_time);
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	trace_break_lease_unblock(inode, new_fl);
 	locks_delete_block(new_fl);
@@ -1659,7 +1659,7 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
 	}
 out:
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 	locks_dispose_list(&dispose);
 	locks_free_lock(new_fl);
 	return error;
@@ -1729,7 +1729,7 @@ int fcntl_getlease(struct file *filp)
 
 	ctx = smp_load_acquire(&inode->i_flctx);
 	if (ctx && !list_empty_careful(&ctx->flc_lease)) {
-		percpu_down_read_preempt_disable(&file_rwsem);
+		percpu_down_read(&file_rwsem);
 		spin_lock(&ctx->flc_lock);
 		time_out_leases(inode, &dispose);
 		list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
@@ -1739,7 +1739,7 @@ int fcntl_getlease(struct file *filp)
 			break;
 		}
 		spin_unlock(&ctx->flc_lock);
-		percpu_up_read_preempt_enable(&file_rwsem);
+		percpu_up_read(&file_rwsem);
 
 		locks_dispose_list(&dispose);
 	}
@@ -1813,7 +1813,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr
 		return -EINVAL;
 	}
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	time_out_leases(inode, &dispose);
 	error = check_conflicting_open(dentry, arg, lease->fl_flags);
@@ -1884,7 +1884,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr
 		lease->fl_lmops->lm_setup(lease, priv);
 out:
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 	locks_dispose_list(&dispose);
 	if (is_deleg)
 		inode_unlock(inode);
@@ -1907,7 +1907,7 @@ static int generic_delete_lease(struct file *filp, void *owner)
 		return error;
 	}
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
 		if (fl->fl_file == filp &&
@@ -1920,7 +1920,7 @@ static int generic_delete_lease(struct file *filp, void *owner)
 	if (victim)
 		error = fl->fl_lmops->lm_change(victim, F_UNLCK, &dispose);
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 	locks_dispose_list(&dispose);
 	return error;
 }
@@ -2643,13 +2643,13 @@ locks_remove_lease(struct file *filp, struct file_lock_context *ctx)
 	if (list_empty(&ctx->flc_lease))
 		return;
 
-	percpu_down_read_preempt_disable(&file_rwsem);
+	percpu_down_read(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list)
 		if (filp == fl->fl_file)
 			lease_modify(fl, F_UNLCK, &dispose);
 	spin_unlock(&ctx->flc_lock);
-	percpu_up_read_preempt_enable(&file_rwsem);
+	percpu_up_read(&file_rwsem);
 
 	locks_dispose_list(&dispose);
 }

include/linux/percpu-rwsem.h

@@ -29,7 +29,7 @@ static struct percpu_rw_semaphore name = {				\
 extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
 extern void __percpu_up_read(struct percpu_rw_semaphore *);
 
-static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *sem)
+static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
 {
 	might_sleep();
 
@@ -47,16 +47,10 @@ static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *
 	__this_cpu_inc(*sem->read_count);
 	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
 		__percpu_down_read(sem, false); /* Unconditional memory barrier */
-	barrier();
 	/*
-	 * The barrier() prevents the compiler from
+	 * The preempt_enable() prevents the compiler from
 	 * bleeding the critical section out.
 	 */
-}
-
-static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
-{
-	percpu_down_read_preempt_disable(sem);
 	preempt_enable();
 }
 
@@ -83,13 +77,9 @@ static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
 	return ret;
 }
 
-static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem)
+static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 {
-	/*
-	 * The barrier() prevents the compiler from
-	 * bleeding the critical section out.
-	 */
-	barrier();
+	preempt_disable();
 	/*
 	 * Same as in percpu_down_read().
 	 */
@@ -102,12 +92,6 @@ static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem
 	rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
 }
 
-static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
-{
-	preempt_disable();
-	percpu_up_read_preempt_enable(sem);
-}
-
 extern void percpu_down_write(struct percpu_rw_semaphore *);
 extern void percpu_up_write(struct percpu_rw_semaphore *);