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SubjectRe: [PATCH tracing/kprobes] kprobes: Disable booster when CONFIG_PREEMPT=y
* Masami Hiramatsu (mhiramat@redhat.com) wrote:
> Disable kprobe booster when CONFIG_PREEMPT=y, because it can't ensure
> that all kernel threads preempted on kprobe's boosted slot run out from
> the slot even using freeze_processes().
>
> The booster on preemptive kernel will be resumed if synchronize_tasks()
> or something like that is introduced.


Yes, given that the freezer does not deal with non-freezable tasks (as
you pointed out in a different thread), I think we cannot rely on it
with CONFIG_PREEMPT.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

>
> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Jim Keniston <jkenisto@us.ibm.com>
> CC: Mathieu Desnoyers <compudj@krystal.dyndns.org>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> ---
>
> arch/ia64/kernel/kprobes.c | 2 +-
> arch/x86/kernel/kprobes.c | 2 +-
> kernel/kprobes.c | 29 ++---------------------------
> 3 files changed, 4 insertions(+), 29 deletions(-)
>
> diff --git a/arch/ia64/kernel/kprobes.c b/arch/ia64/kernel/kprobes.c
> index 9adac44..7026b29 100644
> --- a/arch/ia64/kernel/kprobes.c
> +++ b/arch/ia64/kernel/kprobes.c
> @@ -870,7 +870,7 @@ static int __kprobes pre_kprobes_handler(struct die_args *args)
> return 1;
>
> ss_probe:
> -#if !defined(CONFIG_PREEMPT) || defined(CONFIG_FREEZER)
> +#if !defined(CONFIG_PREEMPT)
> if (p->ainsn.inst_flag == INST_FLAG_BOOSTABLE && !p->post_handler) {
> /* Boost up -- we can execute copied instructions directly */
> ia64_psr(regs)->ri = p->ainsn.slot;
> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
> index 5b8c750..9453815 100644
> --- a/arch/x86/kernel/kprobes.c
> +++ b/arch/x86/kernel/kprobes.c
> @@ -429,7 +429,7 @@ void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
> static void __kprobes setup_singlestep(struct kprobe *p, struct pt_regs *regs,
> struct kprobe_ctlblk *kcb)
> {
> -#if !defined(CONFIG_PREEMPT) || defined(CONFIG_FREEZER)
> +#if !defined(CONFIG_PREEMPT)
> if (p->ainsn.boostable == 1 && !p->post_handler) {
> /* Boost up -- we can execute copied instructions directly */
> reset_current_kprobe();
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index b7df302..9907a03 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -124,30 +124,6 @@ static LIST_HEAD(kprobe_insn_pages);
> static int kprobe_garbage_slots;
> static int collect_garbage_slots(void);
>
> -static int __kprobes check_safety(void)
> -{
> - int ret = 0;
> -#if defined(CONFIG_PREEMPT) && defined(CONFIG_FREEZER)
> - ret = freeze_processes();
> - if (ret == 0) {
> - struct task_struct *p, *q;
> - do_each_thread(p, q) {
> - if (p != current && p->state == TASK_RUNNING &&
> - p->pid != 0) {
> - printk("Check failed: %s is running\n",p->comm);
> - ret = -1;
> - goto loop_end;
> - }
> - } while_each_thread(p, q);
> - }
> -loop_end:
> - thaw_processes();
> -#else
> - synchronize_sched();
> -#endif
> - return ret;
> -}
> -
> /**
> * __get_insn_slot() - Find a slot on an executable page for an instruction.
> * We allocate an executable page if there's no room on existing ones.
> @@ -235,9 +211,8 @@ static int __kprobes collect_garbage_slots(void)
> {
> struct kprobe_insn_page *kip, *next;
>
> - /* Ensure no-one is preepmted on the garbages */
> - if (check_safety())
> - return -EAGAIN;
> + /* Ensure no-one is interrupted on the garbages */
> + synchronize_sched();
>
> list_for_each_entry_safe(kip, next, &kprobe_insn_pages, list) {
> int i;
>
>
> --
> Masami Hiramatsu
>
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
>
> e-mail: mhiramat@redhat.com
>

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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