Messages in this thread | | | Date | Thu, 2 Apr 2009 21:17:30 +0200 | From | Ingo Molnar <> | Subject | Re: [patch 04/18] x86, bts: wait until traced task has been scheduled out |
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* markus.t.metzger@intel.com <markus.t.metzger@intel.com> wrote:
> In order to stop branch tracing for a running task, we need to > first clear the branch tracing control bits before we may free the > tracing buffer. If the traced task is running, the cpu might still > trace that task after the branch trace control bits have cleared. > > Wait until the traced task has been scheduled out before > proceeding. > > A similar problem affects the task debug store context. We first > remove the context, then we need to wait until the task has been > scheduled out before we can free the context memory. > > > Reviewed-by: Oleg Nesterov <oleg@redhat.com> > Signed-off-by: Markus Metzger <markus.t.metzger@intel.com> > --- > arch/x86/kernel/ds.c | 40 40 + 0 - 0 ! > 1 file changed, 40 insertions(+) > > Index: b/arch/x86/kernel/ds.c > =================================================================== > --- a/arch/x86/kernel/ds.c > +++ b/arch/x86/kernel/ds.c > @@ -250,6 +250,40 @@ static DEFINE_PER_CPU(struct ds_context > #define system_context per_cpu(system_context_array, smp_processor_id()) > > > +/* > + * Wait for the traced task to unschedule. > + * > + * This guarantees that the bts trace configuration has been > + * synchronized with the cpu executing the task. > + */ > +static void wait_to_unschedule(struct task_struct *task) > +{
this should be in sched.c and task_is_running() should not be exported from there.
I.e. your original patch which i objected to is probably the right one, but should be named something like "task_wait_context_switch()" - which signals its purpose: that it is to wait for the task to context-switch at least once, so that its ptrace state is installed (or deinstalled) for sure.
Ingo
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