Re: Several tst-robust* tests time out with recent Linux kernel

[Peter Zijlstra]

On Tue, Nov 14, 2023 at 04:31:00PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 14, 2023 at 05:46:43PM +0800, Xi Ruoyao wrote:
> > On Tue, 2023-11-14 at 02:33 +0800, Xi Ruoyao wrote:
> > > Hi,
> > > 
> > > With Linux 6.7.0-rc1, several tst-robust* tests time out on x86_64:
> > > 
> > > FAIL: nptl/tst-robust1
> > > FAIL: nptl/tst-robust3
> > > FAIL: nptl/tst-robust4
> > > FAIL: nptl/tst-robust6
> > > FAIL: nptl/tst-robust7
> > > FAIL: nptl/tst-robust9
> > > 
> > > This does not happen with Linux 6.6.0.  Do you have some clue about
> > > it?
> > 
> > Bisected to the kernel commit:
> > 
> > commit 5694289ce183bc3336407a78c8c722a0b9208f9b (HEAD)
> > Author: peterz@xxxxxxxxxxxxx <peterz@xxxxxxxxxxxxx>
> > Date:   Thu Sep 21 12:45:08 2023 +0200
> > 
> >     futex: Flag conversion
> >     
> >     Futex has 3 sets of flags:
> >     
> >      - legacy futex op bits
> >      - futex2 flags
> >      - internal flags
> >     
> >     Add a few helpers to convert from the API flags into the internal
> >     flags.
> >     
> >     Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> >     Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> >     Reviewed-by: Andr<C3><A9> Almeida <andrealmeid@xxxxxxxxxx>
> >     Link: https://lore.kernel.org/r/20230921105247.722140574@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 
> I can confirm. I'm also going crazy trying to figure out how this
> happens.
> 
> The below is sufficient to make it unhappy...
> 
> /me most puzzled
> 
> ---
> diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
> index b5379c0e6d6d..1a1f9301251f 100644
> --- a/kernel/futex/futex.h
> +++ b/kernel/futex/futex.h
> @@ -17,7 +17,7 @@
>   * restarts.
>   */
>  #ifdef CONFIG_MMU
> -# define FLAGS_SHARED		0x01
> +# define FLAGS_SHARED		0x10
>  #else
>  /*
>   * NOMMU does not have per process address space. Let the compiler optimize

Just the above seems sufficient.