ceph: refactor wake_up_bit() pattern of calling

[ Upstream commit 53db6f2 ]

The wake_up_bit() is called in ceph_async_unlink_cb(),
wake_async_create_waiters(), and ceph_finish_async_create().
It makes sense to switch on clear_bit() function, because
it makes the code much cleaner and easier to understand.
More important rework is the adding of smp_mb__after_atomic()
memory barrier after the bit modification and before
wake_up_bit() call. It can prevent potential race condition
of accessing the modified bit in other threads. Luckily,
clear_and_wake_up_bit() already implements the required
functionality pattern:

static inline void clear_and_wake_up_bit(int bit, unsigned long *word)
{
	clear_bit_unlock(bit, word);
	/* See wake_up_bit() for which memory barrier you need to use. */
	smp_mb__after_atomic();
	wake_up_bit(word, bit);
}

Signed-off-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: dubeyko

fs/ceph/dir.c

@@ -1260,8 +1260,7 @@ static void ceph_async_unlink_cb(struct ceph_mds_client *mdsc,
 	spin_unlock(&fsc->async_unlink_conflict_lock);
 
 	spin_lock(&dentry->d_lock);
-	di->flags &= ~CEPH_DENTRY_ASYNC_UNLINK;
-	wake_up_bit(&di->flags, CEPH_DENTRY_ASYNC_UNLINK_BIT);
+	clear_and_wake_up_bit(CEPH_DENTRY_ASYNC_UNLINK_BIT, &di->flags);
 	spin_unlock(&dentry->d_lock);
 
 	synchronize_rcu();

fs/ceph/file.c

@@ -579,8 +579,7 @@ static void wake_async_create_waiters(struct inode *inode,
 
 	spin_lock(&ci->i_ceph_lock);
 	if (ci->i_ceph_flags & CEPH_I_ASYNC_CREATE) {
-		ci->i_ceph_flags &= ~CEPH_I_ASYNC_CREATE;
-		wake_up_bit(&ci->i_ceph_flags, CEPH_ASYNC_CREATE_BIT);
+		clear_and_wake_up_bit(CEPH_ASYNC_CREATE_BIT, &ci->i_ceph_flags);
 
 		if (ci->i_ceph_flags & CEPH_I_ASYNC_CHECK_CAPS) {
 			ci->i_ceph_flags &= ~CEPH_I_ASYNC_CHECK_CAPS;
@@ -762,8 +761,7 @@ static int ceph_finish_async_create(struct inode *dir, struct inode *inode,
 	}
 
 	spin_lock(&dentry->d_lock);
-	di->flags &= ~CEPH_DENTRY_ASYNC_CREATE;
-	wake_up_bit(&di->flags, CEPH_DENTRY_ASYNC_CREATE_BIT);
+	clear_and_wake_up_bit(CEPH_DENTRY_ASYNC_CREATE_BIT, &di->flags);
 	spin_unlock(&dentry->d_lock);
 
 	return ret;