[GIT PULL] io_uring followup fixes for 5.12-rc4

[GIT PULL] io_uring followup fixes for 5.12-rc4

[Jens Axboe]

Hi Linus,

Was planning on holding these for -rc5, but I think we may as well
flush them out. In this pull request:

- The SIGSTOP change from Eric, so we properly ignore that for
  PF_IO_WORKER threads.

- Disallow sending signals to PF_IO_WORKER threads in general, we're not
  interested in having them funnel back to the io_uring owning task.

- Stable fix from Stefan, ensuring we properly break links for short
  send/sendmsg recv/recvmsg if MSG_WAITALL is set.

- Catch and loop when needing to run task_work before a PF_IO_WORKER
  threads goes to sleep.

Please pull!


The following changes since commit de75a3d3f5a14c9ab3c4883de3471d3c92a8ee78:

  io_uring: don't leak creds on SQO attach error (2021-03-18 09:44:35 -0600)

are available in the Git repository at:

  git://git.kernel.dk/linux-block.git tags/io_uring-5.12-2021-03-21

for you to fetch changes up to 0031275d119efe16711cd93519b595e6f9b4b330:

  io_uring: call req_set_fail_links() on short send[msg]()/recv[msg]() with MSG_WAITALL (2021-03-21 09:41:14 -0600)

----------------------------------------------------------------
io_uring-5.12-2021-03-21

----------------------------------------------------------------
Eric W. Biederman (1):
      signal: don't allow STOP on PF_IO_WORKER threads

Jens Axboe (2):
      signal: don't allow sending any signals to PF_IO_WORKER threads
      io-wq: ensure task is running before processing task_work

Stefan Metzmacher (1):
      io_uring: call req_set_fail_links() on short send[msg]()/recv[msg]() with MSG_WAITALL

 fs/io-wq.c      |  8 ++++++--
 fs/io_uring.c   | 24 ++++++++++++++++++++----
 kernel/signal.c |  6 +++++-
 3 files changed, 31 insertions(+), 7 deletions(-)

-- 
Jens Axboe

Re: [GIT PULL] io_uring followup fixes for 5.12-rc4

[Linus Torvalds]

On Sun, Mar 21, 2021 at 9:38 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> - Catch and loop when needing to run task_work before a PF_IO_WORKER
>   threads goes to sleep.

Hmm. The patch looks fine, but it makes me wonder: why does that code
use test_tsk_thread_flag() and clear_tsk_thread_flag() on current?

It should just use test_thread_flag() and clear_thread_flag().

Now it looks up "current" - which goes through the thread info - and
then looks up the thread from that. It's all kinds of stupid.

It should just have used the thread_info from the beginning, which is
what test_thread_flag() and clear_thread_flag() do.

I see the same broken pattern in both fs/io-wq.c (which is where I
noticed it when looking at the patch) and in fs/io-uring.c.

Please don't do "*_tsk_thread_flag(current, x)", when just
"*_thread_flag(x)" is simpler, and more efficient.

In fact, you should avoid *_tsk_thread_flag() as much as possible in general.

Thread flags should be considered mostly private to that thread - the
exceptions are generally some very low-level system stuff, ie core
signal handling and things like that.

So please change things like

        if (test_tsk_thread_flag(current, TIF_NOTIFY_SIGNAL))

to

        if (test_thread_flag(TIF_NOTIFY_SIGNAL))

etc.

And yes, we have a design mistake in a closely related area:
"signal_pending()" should *not* take the task pointer either, and we
should have the "current thread" separate from "another thread".

Maybe the "signal_pending(current)" makes people think it's a good
idea to pass in "current" to the thread flag checkers. We would have
been better off with "{fatal_,}signal_pending(void)" for the current
task, and "tsk_(fatal_,}signal_pending(tsk)" for the (very few) cases
of checking another task.

Because it really is all kinds of stupid (yes, often historical -
going all the way back to when 'current' was the main model - but now
stupid) to look up "current" to then look up thread data, when these
days, when the basic pattern is

  #define current get_current()
  #define get_current() (current_thread_info()->task)

ioe, the *thread_info* is the primary and quick thing, and "current"
is the indirection, and so if you see code that basically does
"task_thread_info()" on "current", it is literally going back and
forth between the two.

And yes, on architectures that use "THREAD_INFO_IN_TASK" (which does
include x86), the back-and-forth ends up being a non-issue (because
it's just offsets into containing structs) and it doesn't really
matter. But conceptually, patterns like "test_tsk_thread_flag(current,
x)" really are wrong, and on some architectures it generates
potentially *much* worse code.

           Linus

Re: [GIT PULL] io_uring followup fixes for 5.12-rc4

[Jens Axboe]

On 3/21/21 1:57 PM, Linus Torvalds wrote:
> On Sun, Mar 21, 2021 at 9:38 AM Jens Axboe <axboe@kernel.dk> wrote:
>>
>> - Catch and loop when needing to run task_work before a PF_IO_WORKER
>>   threads goes to sleep.
> 
> Hmm. The patch looks fine, but it makes me wonder: why does that code
> use test_tsk_thread_flag() and clear_tsk_thread_flag() on current?
> 
> It should just use test_thread_flag() and clear_thread_flag().
> 
> Now it looks up "current" - which goes through the thread info - and
> then looks up the thread from that. It's all kinds of stupid.
> 
> It should just have used the thread_info from the beginning, which is
> what test_thread_flag() and clear_thread_flag() do.
> 
> I see the same broken pattern in both fs/io-wq.c (which is where I
> noticed it when looking at the patch) and in fs/io-uring.c.
> 
> Please don't do "*_tsk_thread_flag(current, x)", when just
> "*_thread_flag(x)" is simpler, and more efficient.
> 
> In fact, you should avoid *_tsk_thread_flag() as much as possible in general.
> 
> Thread flags should be considered mostly private to that thread - the
> exceptions are generally some very low-level system stuff, ie core
> signal handling and things like that.
> 
> So please change things like
> 
>         if (test_tsk_thread_flag(current, TIF_NOTIFY_SIGNAL))
> 
> to
> 
>         if (test_thread_flag(TIF_NOTIFY_SIGNAL))
> 
> etc.
> 
> And yes, we have a design mistake in a closely related area:
> "signal_pending()" should *not* take the task pointer either, and we
> should have the "current thread" separate from "another thread".
> 
> Maybe the "signal_pending(current)" makes people think it's a good
> idea to pass in "current" to the thread flag checkers. We would have
> been better off with "{fatal_,}signal_pending(void)" for the current
> task, and "tsk_(fatal_,}signal_pending(tsk)" for the (very few) cases
> of checking another task.
> 
> Because it really is all kinds of stupid (yes, often historical -
> going all the way back to when 'current' was the main model - but now
> stupid) to look up "current" to then look up thread data, when these
> days, when the basic pattern is
> 
>   #define current get_current()
>   #define get_current() (current_thread_info()->task)
> 
> ioe, the *thread_info* is the primary and quick thing, and "current"
> is the indirection, and so if you see code that basically does
> "task_thread_info()" on "current", it is literally going back and
> forth between the two.
> 
> And yes, on architectures that use "THREAD_INFO_IN_TASK" (which does
> include x86), the back-and-forth ends up being a non-issue (because
> it's just offsets into containing structs) and it doesn't really
> matter. But conceptually, patterns like "test_tsk_thread_flag(current,
> x)" really are wrong, and on some architectures it generates
> potentially *much* worse code.

Thanks, that's useful information, I guess it just ended up being used
by chance and I didn't realize it made a difference for some archs. I'll
change these, and I also think that io-wq should be a bit nicer and use
tracehook_notify_signal() if TIF_NOTIFY_SIGNAL is set. Doesn't matter
now, but very well might in the future when TIF_NOTIFY_SIGNAL gets
used for more than just task_work notifications.

-- 
Jens Axboe

Re: [GIT PULL] io_uring followup fixes for 5.12-rc4

[pr-tracker-bot]

The pull request you sent on Sun, 21 Mar 2021 10:38:04 -0600:

> git://git.kernel.dk/linux-block.git tags/io_uring-5.12-2021-03-21

has been merged into torvalds/linux.git:
https://git.kernel.org/torvalds/c/2c41fab1c60b02626c8153a1806a7a1e5d62aaf1

Thank you!

-- 
Deet-doot-dot, I am a bot.
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