On Fri, Oct 05, 2018 at 08:45:40PM -0700, Paul E. McKenney wrote: > On Fri, Oct 05, 2018 at 07:46:28PM -0400, Theodore Y. Ts'o wrote: > > On Fri, Oct 05, 2018 at 04:18:09PM -0700, Joel Fernandes (Google) wrote: > > > > > > Here are this week's rcu doc updates based on combing through whatisRCU and > > > checklists. Hopefully you agree with them. I left several old _bh and _sched > > > API references as is, since I don't think its a good idea to remove them till > > > the APIs themselves are removed, however I did remove several of them as well > > > (like in the first patch in this series) since I feel its better to "encourage" > > > new users not to use the old API. > > > > Hi Joel, > > > > As it so happens, I just recently wrote my first RCU patch[1] (file > > systems, especially on-disk data structures, generally tend not to be > > good candidates for RCU semantics). > > > > [1] http://patchwork.ozlabs.org/patch/979779/ > > Very cool! > > One question... In the following hunk: > > ------------------------------------------------------------------------ > > @@ -5353,9 +5362,13 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data) > #ifdef CONFIG_QUOTA > sbi->s_jquota_fmt = old_opts.s_jquota_fmt; > for (i = 0; i < EXT4_MAXQUOTAS; i++) { > - kfree(sbi->s_qf_names[i]); > - sbi->s_qf_names[i] = old_opts.s_qf_names[i]; Could you annotate this pointer (sbi->s_qf_names) with __rcu so it can be checked by sparse for proper usage? Its also point #16 in the checklist.txt RCU document. I enclosed a diff to do this below. I also saw a bunch of places in super.c where the pointer isn't accessed from an rcu read section or rcu_dereference, but it was a quick look so sorry if I missed something. If its true, then are you planning to convert these to use rcu_dereference and wrapped by an rcu_read_lock/unlock as well? > + to_free[i] = rcu_dereference_protected(sbi->s_qf_names[i], > + &sb->s_umount); Also should this be the following? to_free[i] = rcu_dereference_protected(sbi->s_qf_names[i], lockdep_is_held(&sb->s_umount)); > + rcu_assign_pointer(sbi->s_qf_names[i], old_opts.s_qf_names[i]); > } > + for (i = 0; i < EXT4_MAXQUOTAS; i++) > + kfree(to_free[i]); > + synchronize_rcu(); I had same concern as Paul here about synchronize_rcu done before the kfree. thanks, - Joel diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 5863fd22e90b..eec1b3090d04 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c @@ -5083,7 +5083,7 @@ struct ext4_mount_options { u32 s_min_batch_time, s_max_batch_time; #ifdef CONFIG_QUOTA int s_jquota_fmt; - char *s_qf_names[EXT4_MAXQUOTAS]; + char __rcu *s_qf_names[EXT4_MAXQUOTAS]; #endif };
