Date:   Tue, 24 Jan 2023 17:43:47 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Gregory Price <gregory.price@memverge.com>
Cc:     Gregory Price <gourry.memverge@gmail.com>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        krisman@collabora.com, tglx@linutronix.de, luto@kernel.org,
        peterz@infradead.org, ebiederm@xmission.com,
        akpm@linux-foundation.org, adobriyan@gmail.com, corbet@lwn.net,
        shuah@kernel.org, avagin@gmail.com
Subject: Re: [PATCH 3/3] ptrace,syscall_user_dispatch: add a getter/setter
 for sud configuration
Message-ID: <20230124164347.GA28280@redhat.com>
References: <20230123032942.18263-1-gregory.price@memverge.com>
 <20230123032942.18263-4-gregory.price@memverge.com>
 <20230123154101.GA6268@redhat.com>
 <Y87OEdDXwZG8pmmE@memverge.com>
 <20230123195228.GD6268@redhat.com>
 <Y9AAcuomaVM2JRCA@memverge.com>
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I won't really argue, but...

On 01/24, Gregory Price wrote:
>
> On Mon, Jan 23, 2023 at 08:52:29PM +0100, Oleg Nesterov wrote:
> > On 01/23, Gregory Price wrote:
> > >
> > > So i think dropping 2/3 in the list is good.  If you concur i'll do
> > > that.
> >
> > Well I obviously think that 2/3 should be dropped ;)
> >
> > As for 1/3 and 3/3, feel free to add my reviewed-by.
> >
> > Oleg.
> >
>
> I'm actually going to walk my agreement back.
>
> After one more review, the need for the proc/status entry is not to
> decide whether to dump SUD settings, but for use in deciding whether to
> set the SUSPEND_SYSCALL_DISPATCH option from patch 1/3.

Rather than read /proc/pid/status, CRIU can just do
PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG unconditionally
and check syscall_user_dispatch_config.mode ?

Why do want to expose SYSCALL_USER_DISPATCH in /proc/status? If this task
is not stopped you can't trust this value anyway. If it is stopped, I don't
think ptrace(PTRACE_GET_SYSCALL_USER_DISPATCH_CONFIG) is slower than reading
/proc.

but perhaps I missed something?

Oleg.