Re: [RFC PATCH 01/22] kernel/entry/common: Move syscall_enter_from_user_mode_work() out of header

[K Prateek Nayak <kprateek.nayak@amd.com>]

Hello Peter,

Thank you for taking a look.

On 2/20/2025 4:13 PM, Peter Zijlstra wrote:
> On Thu, Feb 20, 2025 at 09:32:36AM +0000, K Prateek Nayak wrote:
>> Retain the prototype of syscall_enter_from_user_mode_work() in
>> linux/entry-common.h and move the function definition to
>> kernel/entry/common.c in preparation to notify the scheduler of task
>> entering and exiting kernel mode for syscall. The two architectures that
>> use it directly (x86, s390) and the four that call it via
>> syscall_enter_from_user_mode() (x86, riscv, loongarch, s390) end up
>> selecting GENERIC_ENTRY, hence, no functional changes are intended.
>>
>> [..snip..]
>>
>> @@ -79,6 +79,16 @@ noinstr void syscall_enter_from_user_mode_prepare(struct pt_regs *regs)
>>   	instrumentation_end();
>>   }
>>   
>> +__always_inline long syscall_enter_from_user_mode_work(struct pt_regs *regs, long syscall)
>> +{
>> +	unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
>> +
>> +	if (work & SYSCALL_WORK_ENTER)
>> +		syscall = syscall_trace_enter(regs, syscall, work);
>> +
>> +	return syscall;
>> +}
>> +
>>   /* Workaround to allow gradual conversion of architecture code */
>>   void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
> 
> This breaks s390. While you retain an external linkage, the function
> looses the noinstr tag that's needed for correctness.
> 
> Also, extern __always_inline is flaky as heck. Please don't do this.

Noted! I'll try to find another way around this.

-- 
Thanks and Regards,
Prateek