linux-kernel - Re: [PATCH 1/2 v2] futex: adjust a futex timeout with a per-timens offset

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Date:   Thu, 15 Oct 2020 17:02:54 +0100
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Andrei Vagin <avagin@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Cc:     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 v2] futex: adjust a futex timeout with a per-timens
 offset

On 10/15/20 5:00 PM, 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>

Reviewed-by: Dmitry Safonov <0x7f454c46@...il.com>

> ---
> 
> v2:
> * check FUTEX_CLOCK_REALTIME properly
> * fix futex_time32 too
> 
>  kernel/futex.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index a5876694a60e..32056d2d4171 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -39,6 +39,7 @@
>  #include <linux/freezer.h>
>  #include <linux/memblock.h>
>  #include <linux/fault-inject.h>
> +#include <linux/time_namespace.h>
>  
>  #include <asm/futex.h>
>  
> @@ -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 (!(op & FUTEX_CLOCK_REALTIME))
> +			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
>  		tp = &t;
>  	}
>  	/*
> @@ -3989,6 +3992,8 @@ SYSCALL_DEFINE6(futex_time32, 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 (!(op & FUTEX_CLOCK_REALTIME))
> +			t = timens_ktime_to_host(CLOCK_MONOTONIC, t);
>  		tp = &t;
>  	}
>  	if (cmd == FUTEX_REQUEUE || cmd == FUTEX_CMP_REQUEUE ||
>

Thanks,
         Dmitry