On Wed, Apr 04, 2012 at 10:04:12PM -0400, Bobby Powers wrote:
> spin_is_locked always returns 0 on non-SMP systems, which causes btrfs
> to fail the mount. There is documentation pending as to why checking
> for spin_is_locked is a bad idea:
>
> https://lkml.org/lkml/2012/3/27/413
>
> The suggested lockdep_assert_held() is not appropriate in this case,
> as what get_restripe_target() is checking for is that either
> volume_mutex is held or balance_lock is held. Luckily
> lockdep_assert_held() is a simple macro:
>
> WARN_ON(debug_locks && !lockdep_is_held(l))
>
> We can mimic the structure in get_restripe_target(), but we need to
> make sure lockdep_is_held() is defined for the !LOCKDEP case.
>
> CC: Ilya Dryomov <idryo...@gmail.com>
> CC: Chris Mason <chris.ma...@oracle.com>
> CC: Andi Kleen <a...@linux.intel.com>
> CC: Jeff Mahoney <je...@suse.de>
> CC: Ingo Molnar <mi...@redhat.com>
> CC: linux-ker...@vger.kernel.org
> Signed-off-by: Bobby Powers <bobbypow...@gmail.com>
> ---
> fs/btrfs/extent-tree.c | 5 +++--
> include/linux/lockdep.h | 1 +
> 2 files changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index a844204..4d13eb1 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -24,6 +24,7 @@
> #include <linux/kthread.h>
> #include <linux/slab.h>
> #include <linux/ratelimit.h>
> +#include <linux/lockdep.h>
> #include "compat.h"
> #include "hash.h"
> #include "ctree.h"
> @@ -3158,8 +3159,8 @@ static u64 get_restripe_target(struct btrfs_fs_info
> *fs_info, u64 flags)
> struct btrfs_balance_control *bctl = fs_info->balance_ctl;
> u64 target = 0;
>
> - BUG_ON(!mutex_is_locked(&fs_info->volume_mutex) &&
> - !spin_is_locked(&fs_info->balance_lock));
> + BUG_ON(debug_locks && !lockdep_is_held(&fs_info->volume_mutex) &&
> + !lockdep_is_held(&fs_info->balance_lock));
>
> if (!bctl)
> return 0;
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index d36619e..94c0edb 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -392,6 +392,7 @@ struct lock_class_key { };
>
> #define lockdep_depth(tsk) (0)
>
> +#define lockdep_is_held(l) (0)
> #define lockdep_assert_held(l) do { } while (0)
>
> #define lockdep_recursing(tsk) (0)
> --
> 1.7.10.rc3.3.g19a6c
OK, Mitch's report prompted me to actually take a look. This patch is
wrong: by defining lockdep_is_held(l) to 0 in !LOCKDEP case you
effectively mimic the behaviour of spin_is_locked() which is what
getting us in the first place.
get_restripe_target() interface is WIP so I will replace BUG_ON with a
comment and send a patch through btrfs tree.
Thanks,
Ilya
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