linux-kernel - Re: [PATCHSET RFC v3 0/6] Add support for TIF_NOTIFY

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Message-ID: <3c3616f2-8801-1d42-6d7d-3dfbf977edb2@kernel.dk>
Date:   Tue, 13 Oct 2020 13:39:35 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Miroslav Benes <mbenes@...e.cz>
Cc:     Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
        io-uring@...r.kernel.org, peterz@...radead.org, tglx@...utronix.de,
        live-patching@...r.kernel.org
Subject: Re: [PATCHSET RFC v3 0/6] Add support for TIF_NOTIFY_SIGNAL

On 10/12/20 11:27 AM, Miroslav Benes wrote:
> On Sat, 10 Oct 2020, Jens Axboe wrote:
> 
>> On 10/9/20 9:21 AM, Jens Axboe wrote:
>>> On 10/9/20 2:01 AM, Miroslav Benes wrote:
>>>> On Thu, 8 Oct 2020, Oleg Nesterov wrote:
>>>>
>>>>> On 10/05, Jens Axboe wrote:
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> The goal is this patch series is to decouple TWA_SIGNAL based task_work
>>>>>> from real signals and signal delivery.
>>>>>
>>>>> I think TIF_NOTIFY_SIGNAL can have more users. Say, we can move
>>>>> try_to_freeze() from get_signal() to tracehook_notify_signal(), kill
>>>>> fake_signal_wake_up(), and remove freezing() from recalc_sigpending().
>>>>>
>>>>> Probably the same for TIF_PATCH_PENDING, klp_send_signals() can use
>>>>> set_notify_signal() rather than signal_wake_up().
>>>>
>>>> Yes, that was my impression from the patch set too, when I accidentally 
>>>> noticed it.
>>>>
>>>> Jens, could you CC our live patching ML when you submit v4, please? It 
>>>> would be a nice cleanup.
>>>
>>> Definitely, though it'd be v5 at this point. But we really need to get
>>> all archs supporting TIF_NOTIFY_SIGNAL first. Once we have that, there's
>>> a whole slew of cleanups that'll fall out naturally:
>>>
>>> - Removal of JOBCTL_TASK_WORK
>>> - Removal of special path for TWA_SIGNAL in task_work
>>> - TIF_PATCH_PENDING can be converted and then removed
>>> - try_to_freeze() cleanup that Oleg mentioned
>>>
>>> And probably more I'm not thinking of right now :-)
>>
>> Here's the current series, I took a stab at converting all archs to
>> support TIF_NOTIFY_SIGNAL so we have a base to build on top of. Most
>> of them were straight forward, but I need someone to fixup powerpc,
>> verify arm and s390.
>>
>> But it's a decent start I think, and means that we can drop various
>> bits as is done at the end of the series. I could swap things around
>> a bit and avoid having the intermediate step, but I envision that
>> getting this in all archs will take a bit longer than just signing off
>> on the generic/x86 bits. So probably best to keep the series as it is
>> for now, and work on getting the arch bits verified/fixed/tested.
>>
>> https://git.kernel.dk/cgit/linux-block/log/?h=tif-task_work
> 
> Thanks, Jens.
> 
> Crude diff for live patching on top of the series is below. Tested only on 
> x86_64, but it passes the tests without an issue.

Nice, thanks!

I'm continuing to hone the series, what's really missing so far is arch
review. Most conversions are straight forward, some I need folks to
definitely take a look at (arm, s390). powerpc is also a bit hair right
now, but I'm told that 5.10 will kill a TIF flag there, so that'll make
it trivial once I rebase on that.

Did a few more cleanups on top, series is in the same spot. I'll repost
once the merge window settles down.

-- 
Jens Axboe