linux-kernel - Re: [PATCH RFC 1/1] futex: Create set_robust

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Message-Id: <df8896f8-3a19-4bde-86b3-8cb1172d0de7@app.fastmail.com>
Date: Fri, 25 Oct 2024 06:33:31 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: André Almeida <andrealmeid@...lia.com>
Cc: "Thomas Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...hat.com>,
 "Davidlohr Bueso" <dave@...olabs.net>, "Darren Hart" <dvhart@...radead.org>,
 "Peter Zijlstra" <peterz@...radead.org>, sonicadvance1@...il.com,
 linux-kernel@...r.kernel.org, kernel-dev@...lia.com,
 linux-api@...r.kernel.org
Subject: Re: [PATCH RFC 1/1] futex: Create set_robust_list2

On Thu, Oct 24, 2024, at 19:55, André Almeida wrote:
> Em 24/10/2024 15:03, André Almeida escreveu:
>> Em 24/10/2024 12:57, Arnd Bergmann escreveu:
>>> On Thu, Oct 24, 2024, at 14:57, André Almeida wrote:
>>>> This new syscall allows to set multiple list to the same process. There
>>>> are two list types: 32 and 64 bit lists.
>>> Assuming we want them to behave the same way, did you intend
>>> ROBUST_LIST_64BIT to refer to 64-bit pointers on 32-bit
>>> tasks, or should they use normal word-size pointers?
>> 
>> Oh right, I haven't covered that indeed. I think I would need to have 
>> something like:
>> 
>> static void exit_robust_list_64()
>> static void exit_robust_list_32()
>> 
>> And then each function would use explicit sizes for pointers. Also, I 
>> would rewrite the conditions to make that every combination of 64/32bit 
>> kernel/app calls the appropriated function.
>
> Something like this:
>
> #ifdef CONFIG_64BIT
> 	if (unlikely(tsk->robust_list)) {
> 		exit_robust_list_64bit(tsk, tsk->robust_list);
> 		tsk->robust_list = NULL;
> 	}
> #else
> 	if (unlikely(tsk->robust_list)) {
> 		exit_robust_list_32bit(tsk, tsk->robust_list);
> 		tsk->robust_list = NULL;
> 	}
> #endif
>
> #ifdef CONFIG_COMPAT
> 	if (unlikely(tsk->compat_robust_list)) {
> 		exit_robust_32bit(tsk, tsk->compat_robust_list);
> 		tsk->compat_robust_list = NULL;
> 	}
> #endif

This should work, but I wonder if it ends up simpler to
instead have tsk->robust_list64 and tsk->robust_list32
entries and just put the #ifdef CONFIG_64BIT around the code
accessing robust_list64.

     Arnd