linux-kernel - Re: [PATCH] io_thread/x86: don't reset 'cs', 'ss', 'ds' and 'es' registers for io

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Message-ID: <5026f7eb-9cf3-065d-009d-fe0fd3e94c2b@kernel.dk>
Date:   Tue, 25 May 2021 13:52:24 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Olivier Langlois <olivier@...llion01.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Stefan Metzmacher <metze@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        io-uring <io-uring@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH] io_thread/x86: don't reset 'cs', 'ss', 'ds' and 'es'
 registers for io_threads

On 5/25/21 1:39 PM, Olivier Langlois wrote:
> On Fri, 2021-05-21 at 03:31 -0400, Olivier Langlois wrote:
>>
>> However, I can reproduce it at will with my real program. So as Linus
>> has suggested, I'll investigate by searching where the PF_IO_WORKER is
>> used.
>>
>> I'll keep the list updated if I discover something.
>>
> I think that I am about to stumble into the key to unravel the mystery
> of my core dump generation issue. I am going ask you a quick question
> and it is very likely to trigger an ahah moment...
> 
> To what value is the task_struct mm field is set to for the io-wkr
> threads?
> 
> If I look in the create_io_thread() function, I can see that CLONE_VM
> isn't set...

It definitely should be, what kernel are you looking at? If CLONE_VM
wasn't set, we'd have various issues with requests accessing user mm.

-- 
Jens Axboe