linux-kernel - Re: [PATCH] livepatch: klp_send_signal should treat PF_IO_WORKER like PF

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Date:   Wed, 24 Mar 2021 22:51:46 -0400
From:   Joe Lawrence <joe.lawrence@...hat.com>
To:     Dong Kai <dongkai11@...wei.com>, jpoimboe@...hat.com,
        jikos@...nel.org, mbenes@...e.cz, pmladek@...e.com
Cc:     axboe@...nel.dk, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] livepatch: klp_send_signal should treat PF_IO_WORKER like
 PF_KTHREAD

On 3/24/21 9:48 PM, Dong Kai wrote:
> commit 15b2219facad ("kernel: freezer should treat PF_IO_WORKER like
> PF_KTHREAD for freezing") is to fix the freezeing issue of IO threads

nit: s/freezeing/freezing

> by making the freezer not send them fake signals.
> 
> Here live patching consistency model call klp_send_signals to wake up
> all tasks by send fake signal to all non-kthread which only check the
> PF_KTHREAD flag, so it still send signal to io threads which may lead to
> freezeing issue of io threads.
> 
> Here we take the same fix action by treating PF_IO_WORKERS as PF_KTHREAD
> within klp_send_signal function.
> 
> Signed-off-by: Dong Kai <dongkai11@...wei.com>
> ---
> note:
> the io threads freeze issue links:
> [1] https://lore.kernel.org/io-uring/YEgnIp43%2F6kFn8GL@kevinlocke.name/
> [2] https://lore.kernel.org/io-uring/d7350ce7-17dc-75d7-611b-27ebf2cb539b@kernel.dk/
> 
>   kernel/livepatch/transition.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> index f6310f848f34..0e1c35c8f4b4 100644
> --- a/kernel/livepatch/transition.c
> +++ b/kernel/livepatch/transition.c
> @@ -358,7 +358,7 @@ static void klp_send_signals(void)
>   		 * Meanwhile the task could migrate itself and the action
>   		 * would be meaningless. It is not serious though.
>   		 */
> -		if (task->flags & PF_KTHREAD) {
> +		if (task->flags & (PF_KTHREAD | PF_IO_WORKER)) {
>   			/*
>   			 * Wake up a kthread which sleeps interruptedly and
>   			 * still has not been migrated.
> 

(PF_KTHREAD | PF_IO_WORKER) is open coded in soo many places maybe this 
is a silly question, but...

If the livepatch code could use fake_signal_wake_up(), we could 
consolidate the pattern in klp_send_signals() with the one in 
freeze_task().  Then there would only one place for wake up / fake 
signal logic.

I don't fully understand the differences in the freeze_task() version, 
so I only pose this as a question and not v2 request.

As it is, this change seems logical to me, so:
Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

Thanks,

-- Joe