On 19.04.2018 19:33, David Sterba wrote:
> The device replace is paused by unmount or read only remount, and
> resumed on next mount or write remount.
>
> The exclusive status should be checked properly as it's a global
> invariant and we must not allow 2 operations run. In this case, the
> balance can be also paused and resumed under same conditions. It's
> always checked first so dev-replace could see the EXCL_OP already taken,
> BUT, the ioctl would never let start both at the same time.
>
> Replace the WARN_ON with message and return 0, indicating no error as
> this is purely theoretical and the user will be informed. Resolving that
> manually should be possible by waiting for the other operation to finish
> or cancel the paused state.
>
> Signed-off-by: David Sterba <dste...@suse.com>
Reviewed-by: Nikolay Borisov <nbori...@suse.com>
> ---
> fs/btrfs/dev-replace.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index 7a87ffad041e..346bd460f8e7 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -908,7 +908,17 @@ int btrfs_resume_dev_replace_async(struct btrfs_fs_info
> *fs_info)
> }
> btrfs_dev_replace_write_unlock(dev_replace);
>
> - WARN_ON(test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags));
> + /*
> + * This could collide with a paused balance, but the exclusive op logic
> + * should never allow both to start and pause. We don't want to allow
> + * dev-replace to start anyway.
> + */
> + if (test_and_set_bit(BTRFS_FS_EXCL_OP, &fs_info->flags)) {
> + btrfs_info(fs_info,
> + "cannot resume dev-replace, other exclusive operation running");
> + return 0;
> + }
> +
> task = kthread_run(btrfs_dev_replace_kthread, fs_info, "btrfs-devrepl");
> return PTR_ERR_OR_ZERO(task);
> }
>
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