From: Jens Axboe <[email protected]>
To: Bijan Mottahedeh <[email protected]>,
Pavel Begunkov <[email protected]>
Cc: [email protected], Minchan Kim <[email protected]>
Subject: Re: [RFC 1/1] io_uring: preserve work->mm since actual work processing may need it
Date: Fri, 10 Apr 2020 20:17:29 -0600 [thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
On 4/10/20 12:09 PM, Bijan Mottahedeh wrote:
> On 4/10/2020 10:51 AM, Pavel Begunkov wrote:
>> On 10/04/2020 19:54, Bijan Mottahedeh wrote:
>>>> As I see, this down_read() from the trace is
>>>> down_read(¤t->mm->mmap_sem), where current->mm is set by use_mm()
>>>> just several lines above your change. So, what do you mean by passing? I
>>>> don't see do_madvise() __explicitly__ accepting mm as an argument.
>>> I think the sequence is:
>>>
>>> io_madvise()
>>> -> do_madvise(NULL, req->work.mm, ma->addr, ma->len, ma->advice)
>>> ^^^^^^^^^^^^
>>> -> down_read(&mm->mmap_sem)
>>>
>>> I added an assert in do_madvise() for a NULL mm value and hit it running the test.
>>>
>>>> What tree do you use? Extra patches on top?
>>> I'm using next-20200409 with no patches.
>> I see, it came from 676a179 ("mm: pass task and mm to do_madvise"), which isn't
>> in Jen's tree.
>>
>> I don't think your patch will do, because it changes mm refcounting with extra
>> mmdrop() in io_req_work_drop_env(). That's assuming it worked well before.
>>
>> Better fix then is to make it ```do_madvise(NULL, current->mm, ...)```
>> as it actually was at some point in the mentioned patch (v5).
>>
> Ok. Jens had suggested to use req->work.mm in the patch comments so
> let's just get him to confirm:
>
> "I think we want to use req->work.mm here - it'll be the same as
> current->mm at this point, but it makes it clear that we're using a
> grabbed mm."
We should just use current->mm, as that matches at that point anyway
since IORING_OP_MADVISE had needs_mm set.
Minchan, can you please make that change?
--
Jens Axboe
next prev parent reply other threads:[~2020-04-11 2:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-09 22:03 [RFC 0/1] io_uring: preserve work->mm since actual work processing may need it Bijan Mottahedeh
2020-04-09 22:03 ` [RFC 1/1] " Bijan Mottahedeh
2020-04-10 8:47 ` Pavel Begunkov
2020-04-10 16:54 ` Bijan Mottahedeh
2020-04-10 17:51 ` Pavel Begunkov
2020-04-10 17:57 ` Pavel Begunkov
2020-04-10 19:09 ` Bijan Mottahedeh
2020-04-11 2:17 ` Jens Axboe [this message]
2020-04-16 20:24 ` Minchan Kim
2020-04-16 20:30 ` Jens Axboe
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
[email protected] \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox