On Wed, Jun 04, 2014 at 03:18:45PM +0400, Kirill Tkhai wrote: > Hi, Peter, > > 04.06.2014, 14:41, "Peter Zijlstra" <[email protected]>: > > A while ago I did a similar patch for some debugging, but looking at it > > again today I realized we should probably fix this anyway. > > > > --- > > Subject: sched: Fix migration_cpu_stop() return value > > > > There are a number of migration_cpu_stop() users; and some actually care > > about the success of the migration. So report this. > > > > In particular migrate_task_to() as used from task_numa_migrate() > > actually tests this return value. > > > > Also change set_cpus_allowed_ptr() to propagate this return value, since > > it already returns other errors. > > > > Cc: Lai Jiangshan <[email protected]> > > Cc: Ingo Molnar <[email protected]> > > Signed-off-by: Peter Zijlstra <[email protected]> > > --- > > kernel/sched/core.c | 15 +++++++++++---- > > 1 file changed, 11 insertions(+), 4 deletions(-) > (snipped everything because of bad email editor) > > In set_cpus_allowed_ptr() p->on_rq branch can not fail. > > We've changed affinity and released rq's lock, so task can migrate > on allowed cpu only (even if migration_cpu_stop fails). > > And it's a little ambiguously how user should react on this EAGAIN.
Try again? So one reason it might fail is because the task got migrated in between the stop_cpu_call(migration_cpu_stop) call getting to __migrate_task(). Esp. if you look at migrate_task_to() its fairly easy to fail this. Currently it reports success, even though we completely failed to migrate. On -EAGAIN, re-evaluate the target and try again (later). Like for the numa case, we'll try again on the next task_numa_migrate() call if its still relevant. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
