linux-kernel - Re: in_compat_syscall() returns from kernel thread for X86

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Message-ID: <20181018024943.GD32577@ZenIV.linux.org.uk>
Date:   Thu, 18 Oct 2018 03:49:43 +0100
From:   Al Viro <viro@...IV.linux.org.uk>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     NeilBrown <neilb@...e.com>, Peter Zijlstra <peterz@...radead.org>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Andrew Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-tip-commits@...r.kernel.org, jsimmons@...radead.org
Subject: Re: in_compat_syscall() returns from kernel thread for X86_32.

On Wed, Oct 17, 2018 at 07:37:42PM -0700, Andy Lutomirski wrote:

> I could get on board with:
> 
> ({WARN_ON_ONCE(current->flags & PF_KTHREAD); true})
> 
> The point of these accessors is to be used *in a syscall*.
> 
> What on Earth is Lustre doing that makes it have this problem?

	Plays with timestamps from a kernel thread, perhaps?
See the old .su joke about adenoidectomy with rectal access
for possible reasons for doing it that way...