Re: [PATCH 3/4] kernel: add support for TIF_NOTIFY_SIGNAL

Jens Axboe
2020-10-09T15:13:30Z

On 10/9/20 8:43 AM, Oleg Nesterov wrote:
> Once again, I am fine with this patch, just a minor comment...
>
> On 10/08, Jens Axboe wrote:
>>
>> --- a/arch/x86/kernel/signal.c
>> +++ b/arch/x86/kernel/signal.c
>> @@ -808,7 +808,10 @@ void arch_do_signal(struct pt_regs *regs)
>> {
>> struct ksignal ksig;
>>
>> - if (get_signal(&ksig)) {
>> + if (test_thread_flag(TIF_NOTIFY_SIGNAL))
>> + tracehook_notify_signal();
>> +
>> + if (task_sigpending(current) && get_signal(&ksig)) {
>
> I suggested to change arch_do_signal() because somehow I like it this way ;)
>
> And because we can easily pass the "ti_work" mask to arch_do_signal() and
> avoid test_thread_flag/task_sigpending.
>
> Hmm. I just noticed that only x86 uses arch_do_signal(), so perhaps you can
> add this change to this patch right now? Up to you.

Sure, we can do that. Incremental on top then looks like the below. I don't
feel that strongly about it, but it is nice to avoid re-testing the flags.

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index cd140bbf8520..ec6490e53dc3 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -804,14 +804,14 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
* want to handle. Thus you cannot kill init even with a SIGKILL even by
* mistake.
*/
-void arch_do_signal(struct pt_regs *regs)
+void arch_do_signal(struct pt_regs *regs, unsigned long ti_work)
{
struct ksignal ksig;

- if (test_thread_flag(TIF_NOTIFY_SIGNAL))
+ if (ti_work & _TIF_NOTIFY_SIGNAL)
tracehook_notify_signal();

- if (task_sigpending(current) && get_signal(&ksig)) {
+ if ((ti_work & _TIF_SIGPENDING) && get_signal(&ksig)) {
/* Whee! Actually deliver the signal. */
handle_signal(&ksig, regs);
return;
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index f4234aaac36c..0360b7e4e39a 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -265,10 +265,11 @@ static __always_inline void arch_exit_to_user_mode(void) { }
/**
* arch_do_signal - Architecture specific signal delivery function
* @regs: Pointer to currents pt_regs
+ * @ti_work task thread info work flags
*
* Invoked from exit_to_user_mode_loop().
*/
-void arch_do_signal(struct pt_regs *regs);
+void arch_do_signal(struct pt_regs *regs, unsigned long ti_work);

/**
* arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 89a068252897..bd3cf6279e94 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -135,7 +135,7 @@ static __always_inline void exit_to_user_mode(void)
}

/* Workaround to allow gradual conversion of architecture code */
-void __weak arch_do_signal(struct pt_regs *regs) { }
+void __weak arch_do_signal(struct pt_regs *regs, unsigned long ti_work) { }

static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
unsigned long ti_work)
@@ -158,7 +158,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
klp_update_patch_state(current);

if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
- arch_do_signal(regs);
+ arch_do_signal(regs, ti_work);

if (ti_work & _TIF_NOTIFY_RESUME) {
tracehook_notify_resume(regs);

--
Jens Axboe