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Commit aba37660 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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fs/locks: Replace lg_global with a percpu-rwsem 



Replace the global part of the lglock with a percpu-rwsem.

Since fcl_lock is a spinlock and itself nests under i_lock, which too
is a spinlock we cannot acquire sleeping locks at
locks_{insert,remove}_global_locks().

We can however wrap all fcl_lock acquisitions with percpu_down_read
such that all invocations of locks_{insert,remove}_global_locks() have
that read lock held.

This allows us to replace the lg_global part of the lglock with the
write side of the rwsem.

In the absense of writers, percpu_{down,up}_read() are free of atomic
instructions. This further avoids the very long preempt-disable
regions caused by lglock on larger machines.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Cc: der.herr@hofr.at
Cc: paulmck@linux.vnet.ibm.com
Cc: riel@redhat.com
Cc: tj@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 11d9684c

fs/locks.c

+21 −0
Original line number Diff line number Diff line
@@ -164,6 +164,7 @@ int lease_break_time = 45; 
 */

DEFINE_STATIC_LGLOCK(file_lock_lglock);

static DEFINE_PER_CPU(struct hlist_head, file_lock_list);

DEFINE_STATIC_PERCPU_RWSEM(file_rwsem);



/*

 * The blocked_hash is used to find POSIX lock loops for deadlock detection.
@@ -587,6 +588,8 @@ static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2) 
/* Must be called with the flc_lock held! */

static void locks_insert_global_locks(struct file_lock *fl)

{

	percpu_rwsem_assert_held(&file_rwsem);



	lg_local_lock(&file_lock_lglock);

	fl->fl_link_cpu = smp_processor_id();

	hlist_add_head(&fl->fl_link, this_cpu_ptr(&file_lock_list));
@@ -596,6 +599,8 @@ static void locks_insert_global_locks(struct file_lock *fl) 
/* Must be called with the flc_lock held! */

static void locks_delete_global_locks(struct file_lock *fl)

{

	percpu_rwsem_assert_held(&file_rwsem);



	/*

	 * Avoid taking lock if already unhashed. This is safe since this check

	 * is done while holding the flc_lock, and new insertions into the list
@@ -915,6 +920,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request) 
			return -ENOMEM;

	}



	percpu_down_read(&file_rwsem);

	spin_lock(&ctx->flc_lock);

	if (request->fl_flags & FL_ACCESS)

		goto find_conflict;
@@ -955,6 +961,7 @@ static int flock_lock_inode(struct inode *inode, struct file_lock *request) 


out:

	spin_unlock(&ctx->flc_lock);

	percpu_up_read(&file_rwsem);

	if (new_fl)

		locks_free_lock(new_fl);

	locks_dispose_list(&dispose);
@@ -991,6 +998,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request, 
		new_fl2 = locks_alloc_lock();

	}



	percpu_down_read(&file_rwsem);

	spin_lock(&ctx->flc_lock);

	/*

	 * New lock request. Walk all POSIX locks and look for conflicts. If
@@ -1162,6 +1170,7 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request, 
	}

 out:

	spin_unlock(&ctx->flc_lock);

	percpu_up_read(&file_rwsem);

	/*

	 * Free any unused locks.

	 */
@@ -1436,6 +1445,7 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type) 
		return error;

	}



	percpu_down_read(&file_rwsem);

	spin_lock(&ctx->flc_lock);



	time_out_leases(inode, &dispose);
@@ -1487,9 +1497,13 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type) 
	locks_insert_block(fl, new_fl);

	trace_break_lease_block(inode, new_fl);

	spin_unlock(&ctx->flc_lock);

	percpu_up_read(&file_rwsem);



	locks_dispose_list(&dispose);

	error = wait_event_interruptible_timeout(new_fl->fl_wait,

						!new_fl->fl_next, break_time);



	percpu_down_read(&file_rwsem);

	spin_lock(&ctx->flc_lock);

	trace_break_lease_unblock(inode, new_fl);

	locks_delete_block(new_fl);
@@ -1506,6 +1520,7 @@ int __break_lease(struct inode *inode, unsigned int mode, unsigned int type) 
	}

out:

	spin_unlock(&ctx->flc_lock);

	percpu_up_read(&file_rwsem);

	locks_dispose_list(&dispose);

	locks_free_lock(new_fl);

	return error;
@@ -1660,6 +1675,7 @@ generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **pr 
		return -EINVAL;

	}



	percpu_down_read(&file_rwsem);

	spin_lock(&ctx->flc_lock);

	time_out_leases(inode, &dispose);

	error = check_conflicting_open(dentry, arg, lease->fl_flags);
@@ -1730,6 +1746,7 @@ 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(&file_rwsem);

	locks_dispose_list(&dispose);

	if (is_deleg)

		inode_unlock(inode);
@@ -1752,6 +1769,7 @@ static int generic_delete_lease(struct file *filp, void *owner) 
		return error;

	}



	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 &&
@@ -1764,6 +1782,7 @@ 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(&file_rwsem);

	locks_dispose_list(&dispose);

	return error;

}
@@ -2703,6 +2722,7 @@ static void *locks_start(struct seq_file *f, loff_t *pos) 
	struct locks_iterator *iter = f->private;



	iter->li_pos = *pos + 1;

	percpu_down_write(&file_rwsem);

	lg_global_lock(&file_lock_lglock);

	spin_lock(&blocked_lock_lock);

	return seq_hlist_start_percpu(&file_lock_list, &iter->li_cpu, *pos);
@@ -2721,6 +2741,7 @@ static void locks_stop(struct seq_file *f, void *v) 
{

	spin_unlock(&blocked_lock_lock);

	lg_global_unlock(&file_lock_lglock);

	percpu_up_write(&file_rwsem);

}



static const struct seq_operations locks_seq_operations = {