lkml.org 
[lkml]   [2012]   [Jan]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] memcg: restore ss->id_lock to spinlock, using RCU for next
From
Date
Le jeudi 19 janvier 2012 à 04:28 -0800, Tejun Heo a écrit :
> Hello,
>
> On Wed, Jan 18, 2012 at 11:33 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > Interesting, but should be a patch on its own.
>
> Yeap, agreed.
>
> > Maybe other idr users can benefit from your idea as well, if patch is
> > labeled "idr: allow idr_get_next() from rcu_read_lock" or something...
> >
> > I suggest introducing idr_get_next_rcu() helper to make the check about
> > rcu cleaner.
> >
> > idr_get_next_rcu(...)
> > {
> > WARN_ON_ONCE(!rcu_read_lock_held());
> > return idr_get_next(...);
> > }
>
> Hmmm... I don't know. Does having a separate set of interface help
> much? It's easy to avoid/miss the test by using the other one. If we
> really worry about it, maybe indicating which locking is to be used
> during init is better? We can remember the lockdep map and trigger
> WARN_ON_ONCE() if neither the lock or RCU read lock is held.


There is a rcu_dereference_raw(ptr) in idr_get_next()

This could be changed to rcu_dereference_check(ptr, condition) to get
lockdep support for free :)

[ condition would be the appropriate
lockdep_is_held(&the_lock_protecting_my_idr) or 'I use the rcu variant'
and I hold rcu_read_lock ]

This would need to add a 'condition' parameter to idr_gen_next(), but we
have very few users in kernel at this moment.



--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2012-01-19 14:33    [W:0.081 / U:1.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site