btrfs: don't set lock_owner when locking extent buffer for reading

In 731044a98001 "btrfs: switch extent buffer tree lock to rw_semaphore"
the functions for tree read locking were rewritten, and in the process
the read lock functions started setting eb->lock_owner = current->pid.
Previously lock_owner was only set in tree write lock functions.

Read locks are shared, so they don't have exclusive ownership of the
underlying object, so setting lock_owner to any single value for a
read lock makes no sense.  It's mostly harmless because write locks
and read locks are mutually exclusive, and none of the existing code
in btrfs (btrfs_init_new_buffer and print_eb_refs_lock) cares what
nonsense is written in lock_owner when no writer is holding the lock.

KCSAN does care, and will complain about the data race incessantly.
Remove the assignments in the read lock functions because they're
useless noise.

Fixes: 731044a98001 ("btrfs: switch extent buffer tree lock to rw_semaphore")
CC: stable@vger.kernel.org # 5.15+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
index 313d9d685adb7af91b7e8a3674d2d142170716cf..33461b4f9c8b5c3023756f770fe7176f0a5f5103 100644 (file)
--- a/fs/btrfs/locking.c
+++ b/fs/btrfs/locking.c
@@ -45,7 +45,6 @@ void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting ne
                start_ns = ktime_get_ns();
 
        down_read_nested(&eb->lock, nest);
-       eb->lock_owner = current->pid;
        trace_btrfs_tree_read_lock(eb, start_ns);
 }
 
@@ -62,7 +61,6 @@ void btrfs_tree_read_lock(struct extent_buffer *eb)
 int btrfs_try_tree_read_lock(struct extent_buffer *eb)
 {
        if (down_read_trylock(&eb->lock)) {
-               eb->lock_owner = current->pid;
                trace_btrfs_try_tree_read_lock(eb);
                return 1;
        }
@@ -90,7 +88,6 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb)
 void btrfs_tree_read_unlock(struct extent_buffer *eb)
 {
        trace_btrfs_tree_read_unlock(eb);
-       eb->lock_owner = 0;
        up_read(&eb->lock);
 }