linux-kernel - Re: futex timeout not working? (bisected)

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Date:	Fri, 16 Oct 2015 13:50:03 +0200
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Stefan Liebler <stli@...ux.vnet.ibm.com>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: futex timeout not working? (bisected)

On Fri, Oct 16, 2015 at 12:54:51PM +0200, Heiko Carstens wrote:
> > > So you are saying this works on x86 and it must be some s390 specific bug?
> > 
> > Looks like. I have no idea why that would break on s390. Did you try
> > to revert the commit on top of tree?
> 
> Reverting the patch isn't easy due to all the dependencies the code has in
> the meantime. However the following code snippet does logically revert the
> patch and it works again:
> 
> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
> index 3739ac6aa473..c97dd1cc9bd5 100644
> --- a/kernel/time/timekeeping.c
> +++ b/kernel/time/timekeeping.c
> @@ -1953,12 +1953,10 @@ ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
>  		nsecs = timekeeping_get_ns(&tk->tkr_mono);
>  		base = ktime_add_ns(base, nsecs);
>  
> -		if (*cwsseq != tk->clock_was_set_seq) {
> -			*cwsseq = tk->clock_was_set_seq;
> -			*offs_real = tk->offs_real;
> -			*offs_boot = tk->offs_boot;
> -			*offs_tai = tk->offs_tai;
> -		}
> +		*cwsseq = tk->clock_was_set_seq;
> +		*offs_real = tk->offs_real;
> +		*offs_boot = tk->offs_boot;
> +		*offs_tai = tk->offs_tai;

Adding the patch below also "fixes" this. Right now I don't see why this
could architecture specific. Hmm.

diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 3739ac6aa473..75771b15647c 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1835,7 +1835,7 @@ void update_wall_time(void)
 	 * memcpy under the tk_core.seq against one before we start
 	 * updating.
 	 */
-	timekeeping_update(tk, clock_set);
+	timekeeping_update(tk, clock_set | TK_CLOCK_WAS_SET);
 	memcpy(real_tk, tk, sizeof(*tk));
 	/* The memcpy must come last. Do not put anything here! */
 	write_seqcount_end(&tk_core.seq);

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