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Subject: Re: [PATCH 3/4] kernel: add support for TIF_NOTIFY_SIGNAL
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     linux-kernel@vger.kernel.org, io-uring@vger.kernel.org,
        peterz@infradead.org, tglx@linutronix.de
References: <20201008152752.218889-1-axboe@kernel.dk>
 <20201008152752.218889-4-axboe@kernel.dk> <20201009144328.GB14523@redhat.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <e8319a4c-334a-e888-7d31-f43b4ae6822a@kernel.dk>
Date:   Fri, 9 Oct 2020 09:13:20 -0600
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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