On Fri, Oct 20, 2017 at 08:43:39AM +0900, Masami Hiramatsu wrote: > We want to wait for all potentially preempted kprobes trampoline > execution to have completed. This guarantees that any freed > trampoline memory is not in use by any task in the system anymore. > synchronize_rcu_tasks() gives such a guarantee, so use it. > Also, this guarantees to wait for all potentially preempted tasks > on the instructions which will be replaced with a jump. > > Since this becomes a problem only when CONFIG_PREEMPT=y, enable > CONFIG_TASKS_RCU=y for synchronize_rcu_tasks() in that case. > > Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
;-) Acked-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > --- > arch/Kconfig | 2 +- > kernel/kprobes.c | 14 ++++++++------ > 2 files changed, 9 insertions(+), 7 deletions(-) > > diff --git a/arch/Kconfig b/arch/Kconfig > index d789a89cb32c..7e67191a4961 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -90,7 +90,7 @@ config STATIC_KEYS_SELFTEST > config OPTPROBES > def_bool y > depends on KPROBES && HAVE_OPTPROBES > - depends on !PREEMPT > + select TASKS_RCU if PREEMPT > > config KPROBES_ON_FTRACE > def_bool y > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 15fba7fe57c8..a8fc1492b308 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -573,13 +573,15 @@ static void kprobe_optimizer(struct work_struct *work) > do_unoptimize_kprobes(); > > /* > - * Step 2: Wait for quiesence period to ensure all running interrupts > - * are done. Because optprobe may modify multiple instructions > - * there is a chance that Nth instruction is interrupted. In that > - * case, running interrupt can return to 2nd-Nth byte of jump > - * instruction. This wait is for avoiding it. > + * Step 2: Wait for quiesence period to ensure all potentially > + * preempted tasks to have normally scheduled. Because optprobe > + * may modify multiple instructions, there is a chance that Nth > + * instruction is preempted. In that case, such tasks can return > + * to 2nd-Nth byte of jump instruction. This wait is for avoiding it. > + * Note that on non-preemptive kernel, this is transparently converted > + * to synchronoze_sched() to wait for all interrupts to have completed. > */ > - synchronize_sched(); > + synchronize_rcu_tasks(); > > /* Step 3: Optimize kprobes after quiesence period */ > do_optimize_kprobes(); >
