linux-kernel - RE: [PATCH 2/2] futex, x86/mce: Avoid double machine checks

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Message-ID: <4493a015ffcd4d82bbea7d1e5c2e73e4@intel.com>
Date:   Fri, 8 Jan 2021 23:08:58 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Borislav Petkov <bp@...en8.de>, "x86@...nel.org" <x86@...nel.org>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Darren Hart <dvhart@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: [PATCH 2/2] futex, x86/mce: Avoid double machine checks

> I think this is horrid; why can't we have it return something different
> then -EFAULT instead?

I did consider this ... but it appears that architectures aren't unified in the
return value from get_user()

Here's another function involved in the futex call chain leading to this:

static int get_futex_value_locked(u32 *dest, u32 __user *from)
{
        int ret;

        pagefault_disable();
        ret = __get_user(*dest, from);
        pagefault_enable();

        return ret ? -EFAULT : 0;
}

It seems like the expectation here is just "zero or not" and we
don't care what the "not" value is ... just turn it into -EFAULT.

-Tony