btrfs: avoid monopolizing a core when activating a swap file

commit 2c8507c63f5498d4ee4af404a8e44ceae4345056 upstream.

This commit re-attempts the backport of the change to the linux-5.15.y
branch. Commit 214d92f0a465 ("btrfs: avoid monopolizing a core when
activating a swap file") on this branch was reverted.

During swap activation we iterate over the extents of a file and we can
have many thousands of them, so we can end up in a busy loop monopolizing
a core. Avoid this by doing a voluntary reschedule after processing each
extent.

CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8f048e517e656ed1b2b123531f867e23a5a9bde1..d6e43c94436d4ab0c9b23b6dee2e97b1c111ab43 100644 (file)
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -11031,6 +11031,8 @@ static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
                }
 
                start += len;
+
+               cond_resched();
        }
 
        if (bsi.block_len)