linux-kernel - Re: [PATCH 3/3] ptrace,syscall_user_dispatch: add a getter/setter for sud configuration

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Message-ID: <20230124164347.GA28280@redhat.com>
Date:   Tue, 24 Jan 2023 17:43:47 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Gregory Price <gregory.price@...verge.com>
Cc:     Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        krisman@...labora.com, tglx@...utronix.de, luto@...nel.org,
        peterz@...radead.org, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, adobriyan@...il.com, corbet@....net,
        shuah@...nel.org, avagin@...il.com
Subject: Re: [PATCH 3/3] ptrace,syscall_user_dispatch: add a getter/setter
 for sud configuration

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.