On Fri, Mar 06, 2020 at 04:25:27PM +0100, David Sterba wrote: > On Fri, Mar 06, 2020 at 07:30:24PM +0530, Madhuparna Bhowmik wrote: > > On Fri, Mar 06, 2020 at 03:16:53PM +0800, Qu Wenruo wrote: > > > > > > > > > On 2020/3/6 下午2:52, madhuparnabhowmik10@xxxxxxxxx wrote: > > > > From: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx> > > > > > > > > The space_info list is rcu protected. > > > > Hence, it should be traversed with rcu_read_lock held. > > > > > > > > Warning: > > > > [ 29.104591] ============================= > > > > [ 29.104756] WARNING: suspicious RCU usage > > > > [ 29.105046] 5.6.0-rc4-next-20200305 #1 Not tainted > > > > [ 29.105231] ----------------------------- > > > > [ 29.105401] fs/btrfs/block-group.c:2011 RCU-list traversed in non-reader section!! > > > > > > > > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx> > > > > Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@xxxxxxxxx> > > > > --- > > > > fs/btrfs/block-group.c | 4 +++- > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c > > > > index 404e050ce8ee..9cabeef66f5b 100644 > > > > --- a/fs/btrfs/block-group.c > > > > +++ b/fs/btrfs/block-group.c > > > > @@ -1987,6 +1987,7 @@ int btrfs_read_block_groups(struct btrfs_fs_info *info) > > > > > > This function is only triggered at mount time, where no other rcu > > > operation can happen. > > > > > Thanks Qu. > > > > Joel and Paul, what should we do in this case? > > Should we just pass cond = true or use list_for_each_entry instead? > > I think we can afford to add rcu lock/unlock, even if it's not strictly > necessary due to the single threaded context where the function is run. > There are some lightweight operations inside and inc_block_group starts > with two spin locks so there's nothing we'd be losing with disabled > preemption from the caller. I think use list_for_each_entry(). thanks, - Joel
