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    SubjectRe: [PATCH] sched: missing locking in sched_domains code
    On Mon, 28 Apr 2008 09:09:46 +0200 Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

    > On Sun, Apr 27, 2008 at 06:39:26PM -0700, Andrew Morton wrote:
    > > On Sun, 27 Apr 2008 23:12:24 +0200 Heiko Carstens <heiko.carstens@de.ibm.com> wrote:
    > > > Index: linux-2.6/kernel/cpuset.c
    > > > ===================================================================
    > > > --- linux-2.6.orig/kernel/cpuset.c
    > > > +++ linux-2.6/kernel/cpuset.c
    > > > @@ -684,7 +684,9 @@ restart:
    > > > rebuild:
    > > > /* Have scheduler rebuild sched domains */
    > > > get_online_cpus();
    > > > + mutex_lock(&sched_domains_mutex);
    > > > partition_sched_domains(ndoms, doms, dattr);
    > > > + mutex_unlock(&sched_domains_mutex);
    > > > put_online_cpus();
    > > >
    > >
    > > It seems a bit fragile to take this lock in the caller without even adding
    > > a comment at the callee site which documents the new locking rule.
    > >
    > > It would be more robust to take the lock within partition_sched_domains().
    > >
    > > partition_sched_domains() already covers itself with lock_doms_cur(). Can
    > > we take that in arch_reinit_sched_domains() rather than adding the new lock?
    >
    > I think you meant taking it in partition_sched_domains?

    What I meant was: rather than adding the new sched_domains_mutex, can we
    instead call lock_doms_cur() from arch_reinit_sched_domains() and
    sched_init_smp()? Borrow the existing lock?

    Whether that makes sense depends upon what lock_doms_cur() semantically
    *means*. As that appears to be somewhat of a secret, we get to decide ;)




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