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[2/3] ceph: clean up locking annotation for ceph_get_snap_realm and __lookup_snap_realm

Message ID 20210603165231.110559-3-jlayton@kernel.org (mailing list archive)
State New, archived
Headers show
Series ceph: locking fixes for snaprealm handling | expand

Commit Message

Jeff Layton June 3, 2021, 4:52 p.m. UTC
They both say that the snap_rwsem must be held for write, but I don't
see any real reason for it, and it's not currently always called that
way.

The lookup is just walking the rbtree, so holding it for read should be
fine there. The "get" is bumping the refcount and (possibly) removing
it from the empty list. I see no need to hold the snap_rwsem for write
for that.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/ceph/snap.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Ilya Dryomov June 21, 2021, 8:48 p.m. UTC | #1
On Thu, Jun 3, 2021 at 6:52 PM Jeff Layton <jlayton@kernel.org> wrote:
>
> They both say that the snap_rwsem must be held for write, but I don't
> see any real reason for it, and it's not currently always called that
> way.
>
> The lookup is just walking the rbtree, so holding it for read should be
> fine there. The "get" is bumping the refcount and (possibly) removing
> it from the empty list. I see no need to hold the snap_rwsem for write
> for that.
>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>  fs/ceph/snap.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
> index bc6c33d485e6..f8cac2abab3f 100644
> --- a/fs/ceph/snap.c
> +++ b/fs/ceph/snap.c
> @@ -60,12 +60,12 @@
>  /*
>   * increase ref count for the realm
>   *
> - * caller must hold snap_rwsem for write.
> + * caller must hold snap_rwsem.
>   */
>  void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
>                          struct ceph_snap_realm *realm)
>  {
> -       lockdep_assert_held_write(&mdsc->snap_rwsem);
> +       lockdep_assert_held(&mdsc->snap_rwsem);
>
>         dout("get_realm %p %d -> %d\n", realm,
>              atomic_read(&realm->nref), atomic_read(&realm->nref)+1);
> @@ -139,7 +139,7 @@ static struct ceph_snap_realm *ceph_create_snap_realm(
>  /*
>   * lookup the realm rooted at @ino.
>   *
> - * caller must hold snap_rwsem for write.
> + * caller must hold snap_rwsem.
>   */
>  static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
>                                                    u64 ino)
> @@ -147,7 +147,7 @@ static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
>         struct rb_node *n = mdsc->snap_realms.rb_node;
>         struct ceph_snap_realm *r;
>
> -       lockdep_assert_held_write(&mdsc->snap_rwsem);
> +       lockdep_assert_held(&mdsc->snap_rwsem);
>
>         while (n) {
>                 r = rb_entry(n, struct ceph_snap_realm, node);
> --
> 2.31.1
>

Ah, since you are relaxing the requirement some of those lockdep
asserts from the previous patch aren't actually redundant.  This seems
fine to me: lookup definitely doesn't need the write lock and allowing
concurrent gets should be OK.  The write lock made some sense back when
get was an atomic_read followed by atomic_inc but not now.

Reviewed-by: Ilya Dryomov <idryomov@gmail.com>

Thanks,

                Ilya
diff mbox series

Patch

diff --git a/fs/ceph/snap.c b/fs/ceph/snap.c
index bc6c33d485e6..f8cac2abab3f 100644
--- a/fs/ceph/snap.c
+++ b/fs/ceph/snap.c
@@ -60,12 +60,12 @@ 
 /*
  * increase ref count for the realm
  *
- * caller must hold snap_rwsem for write.
+ * caller must hold snap_rwsem.
  */
 void ceph_get_snap_realm(struct ceph_mds_client *mdsc,
 			 struct ceph_snap_realm *realm)
 {
-	lockdep_assert_held_write(&mdsc->snap_rwsem);
+	lockdep_assert_held(&mdsc->snap_rwsem);
 
 	dout("get_realm %p %d -> %d\n", realm,
 	     atomic_read(&realm->nref), atomic_read(&realm->nref)+1);
@@ -139,7 +139,7 @@  static struct ceph_snap_realm *ceph_create_snap_realm(
 /*
  * lookup the realm rooted at @ino.
  *
- * caller must hold snap_rwsem for write.
+ * caller must hold snap_rwsem.
  */
 static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
 						   u64 ino)
@@ -147,7 +147,7 @@  static struct ceph_snap_realm *__lookup_snap_realm(struct ceph_mds_client *mdsc,
 	struct rb_node *n = mdsc->snap_realms.rb_node;
 	struct ceph_snap_realm *r;
 
-	lockdep_assert_held_write(&mdsc->snap_rwsem);
+	lockdep_assert_held(&mdsc->snap_rwsem);
 
 	while (n) {
 		r = rb_entry(n, struct ceph_snap_realm, node);