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Date:   Mon, 22 May 2023 19:47:58 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     Mike Christie <michael.christie@oracle.com>
Cc:     linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk,
        ebiederm@xmission.com, torvalds@linux-foundation.org,
        linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, mst@redhat.com,
        sgarzare@redhat.com, jasowang@redhat.com, stefanha@redhat.com,
        brauner@kernel.org
Subject: Re: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps
 regression
Message-ID: <20230522174757.GC22159@redhat.com>
References: <20230522025124.5863-1-michael.christie@oracle.com>
 <20230522025124.5863-4-michael.christie@oracle.com>
 <20230522123029.GA22159@redhat.com>
 <cfca7764-d210-6df9-e182-2c093101c6cf@oracle.com>
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On 05/22, Mike Christie wrote:
>
> On 5/22/23 7:30 AM, Oleg Nesterov wrote:
> >> +			/*
> >> +			 * When we get a SIGKILL our release function will
> >> +			 * be called. That will stop new IOs from being queued
> >> +			 * and check for outstanding cmd responses. It will then
> >> +			 * call vhost_task_stop to tell us to return and exit.
> >> +			 */
> >
> > But who will call the release function / vhost_task_stop() and when this
> > will happen after this thread gets SIGKILL ?
>
> When we get a SIGKILL, the thread that owns the device/vhost_task will
> also exit since it's the same thread group and it does:
>
> do_exit -> exit_files -> put_files_struct -> close_files -> fput

Ah. thanks. I confused CLONE_FS in vhost_task_create() with CLONE_FILES.

> > Also. Suppose that vhost_worker() dequeues SIGKILL and clears TIF_SIGPENDING.
> >
> > SIGSTOP, PTRACE_INTERRUPT, freezer can come and set TIF_SIGPENDING again.
> > In this case the main for (;;) loop will spin without sleeping until
> > vhost_task_should_stop() becomes true?
>
> I see. So I either have to be able to call get_signal after SIGKILL or
> at this time work like a kthread and ignore signals like a
>
> if (dead && signal_pending())
> 	flush_signals()
> ?

Right now I think that "int dead" should die, and you should simply do
get_signal() + clear(SIGPENDING) if signal_pending() == T , but let me
think tomorrow.

Oleg.