Re: [PATCH 11/11] btrfs: use non-RCU list traversal in write_all_supers callees

[David Sterba <dsterba@suse.cz>]

On Thu, Nov 02, 2017 at 11:49:15AM +0200, Nikolay Borisov wrote:
> 
> 
> On 31.10.2017 19:44, David Sterba wrote:
> > We take the fs_devices::device_list_mutex mutex in write_all_supers
> > which will prevent any add/del changes to the device list. Therefore we
> > don't need to use the RCU variant list_for_each_entry_rcu in any of the
> > called functions.
> > 
> > Signed-off-by: David Sterba <dsterba@suse.com>
> > ---
> >  fs/btrfs/disk-io.c | 9 +++++----
> >  1 file changed, 5 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > index efce9a2fa9be..042cf46e4cd0 100644
> > --- a/fs/btrfs/disk-io.c
> > +++ b/fs/btrfs/disk-io.c
> > @@ -3396,9 +3396,10 @@ static int barrier_all_devices(struct btrfs_fs_info *info)
> >  	int errors_wait = 0;
> >  	blk_status_t ret;
> >  
> > +	WARN_ON(!mutex_is_locked(&info->fs_devices->device_list_mutex));
> 
> Don't we want lockdep_assert_held ? I'm assuming enough testing with
> lockdep on is performed so it will be caught in time if this invariant
> is broken.

Yes, lockdep_assert_held should enough, this is a development-time
warning. Will be fixed.