[lkml]   [2007]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [RFC] cpuset update_cgroup_cpus_allowed
    David wrote:
    > Why can't you just add a helper function to sched.c:
    > void set_hotcpus_allowed(struct task_struct *task,
    > cpumask_t cpumask)
    > {
    > mutex_lock(&sched_hotcpu_mutex);
    > set_cpus_allowed(task, cpumask);
    > mutex_unlock(&sched_hotcpu_mutex);
    > }
    > And then change each task's cpus_allowed via that function instead of
    > set_cpus_allowed() directly?

    I guess this would avoid race conditions within the set_cpus_allowed()
    routine, between its code to read the cpu_online_map and set the tasks
    cpus_allowed ... though if that's useful, don't we really need to add
    locking/unlocking on sched_hotcpu_mutex right inside the
    set_cpus_allowed() routine, for all users of set_cpus_allowed ??

    But I don't see where the above code helps at all deal with the
    races I considered in my previous message:

    > My solution may be worse than that. Because set_cpus_allowed() will
    > fail if asked to set a non-overlapping cpumask, my solution could never
    > terminate. If asked to set a cpusets cpus to something that went off
    > line right then, this I'd guess this code could keep looping forever,
    > looking for cpumasks that didn't match, and then not noticing that it
    > was failing to set them so as they would match.

    These races involve reading the tasks cpuset cpus_allowed mask, reading
    the online map, and both reading and writing the tasks task_struct
    cpus_allowed. Unless one holds the relevant lock for the entire
    interval surrounding the critical accesses to these values, it won't do
    any good that I can see. Just briefly holding a lock around each
    separate access is useless.

    I won't rest till it's the best ...
    Programmer, Linux Scalability
    Paul Jackson <> 1.925.600.0401
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2007-10-16 11:19    [W:0.044 / U:6.720 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site