linux-kernel - Re: [PATCH 1/2] futex: adjust a futex timeout with a per-timens offset

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Date:   Fri, 16 Oct 2020 01:18:53 -0700
From:   Andrei Vagin <avagin@...il.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dmitry Safonov <0x7f454c46@...il.com>,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Shuah Khan <shuah@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH 1/2] futex: adjust a futex timeout with a per-timens
 offset

On Thu, Oct 15, 2020 at 04:13:42PM +0200, Thomas Gleixner wrote:
> On Thu, Oct 15 2020 at 14:26, Dmitry Safonov wrote:
> 
> > On 10/15/20 8:29 AM, Andrei Vagin wrote:
> >> For all commands except FUTEX_WAIT, timeout is interpreted as an
> >> absolute value. This absolute value is inside the task's time namespace
> >> and has to be converted to the host's time.
> >> 
> >> Cc: <stable@...r.kernel.org>
> >> Fixes: 5a590f35add9 ("posix-clocks: Wire up clock_gettime() with timens offsets")
> >> Reported-by: Hans van der Laan <j.h.vanderlaan@...dent.utwente.nl>
> >> Signed-off-by: Andrei Vagin <avagin@...il.com>[..]
> >> @@ -3797,6 +3798,8 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
> >>  		t = timespec64_to_ktime(ts);
> >>  		if (cmd == FUTEX_WAIT)
> >>  			t = ktime_add_safe(ktime_get(), t);
> >> +		else if (!(cmd & FUTEX_CLOCK_REALTIME))
> >> +			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
> >
> > Err, it probably should be
> > : else if (!(op & FUTEX_CLOCK_REALTIME))

Dmitry, thank you for catching this.

> 
> Duh, you are right. I stared at it for a while and did not spot it.
> 
> > And there's also
> > : SYSCALL_DEFINE6(futex_time32, ...)
> > which wants to be patched.
> 
> Indeed. I zapped the commits.

I sent a new version. This time, I extended the test to check
FUTEX_CLOCK_REALTIME and I compiled and run the compat version.
Everything works as it should be.

Thanks,
Andrei