lkml.org 
[lkml]   [2012]   [Jan]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] memcg: restore ss->id_lock to spinlock, using RCU for next
    On Thu, 19 Jan 2012, Eric Dumazet wrote:
    > 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.

    Okay, in that case I'd better split into three (idr, revert, remove lock).
    I'll send those three in a moment. I've also slipped an RCU comment from
    idr_find into idr_get_next, and put the Acks in all three.

    > >
    > > > 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.

    idr_get_next() was introduced for memcg, and has only one other user
    user in the tree (drivers/mtd/mtdcore.c, which uses a mutex to lock it).
    With the RCU fix, idr_get_next() becomes very much like idr_find().
    I'll leave any fiddling with their interfaces to you guys.

    Hugh
    \
     
     \ /
      Last update: 2012-01-19 21:49    [W:0.029 / U:148.900 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site