Messages in this thread | | | Date | Fri, 6 Apr 2012 23:05:55 +0300 | From | Ilya Dryomov <> | Subject | Re: [PATCH v2] Btrfs, lockdep: get_restripe_target: use lockdep in BUG_ON |
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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 <idryomov@gmail.com> > CC: Chris Mason <chris.mason@oracle.com> > CC: Andi Kleen <ak@linux.intel.com> > CC: Jeff Mahoney <jeffm@suse.de> > CC: Ingo Molnar <mingo@redhat.com> > CC: linux-kernel@vger.kernel.org > Signed-off-by: Bobby Powers <bobbypowers@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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