linux-kernel - Re: [BUG 4.4.178] x86_64 compat mode futexes broken

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Date:   Thu, 6 Jun 2019 16:11:30 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Joe Korty <Joe.Korty@...current-rt.com>
Cc:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alistair Strachan <astrachan@...gle.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com
Subject: Re: [BUG 4.4.178] x86_64 compat mode futexes broken

On Thu, Jun 06, 2019 at 09:11:43PM +0000, Joe Korty wrote:
> Starting with 4.4.178, the LTP test
> 
>   pthread_cond_wait/2-3
> 
> when compiled on x86_64 with 'gcc -m32', started failing.  It generates this log output:
> 
>   [16:18:38]Implementation supports the MONOTONIC CLOCK but option is disabled in test.           
>   [16:18:38]Test starting
>   [16:18:38] Process-shared primitive will be tested
>   [16:18:38] Alternative clock for cond will be tested
>   [16:18:38]Test 2-3.c FAILED: The child did not own the mutex inside the cleanup handler
> 

What is the exact build command + test case command? I'd like to
reproduce this myself.

> A git bisection between 4.4.177..178 shows that this commit is the culprit:
> 
>   Git-Commit: 79739ad2d0ac5787a15a1acf7caaf34cd95bbf3c
>   Author: Alistair Strachan <astrachan@...gle.com>
>   Subject: [PATCH] x86: vdso: Use $LD instead of $CC to link
> 

Have you tested 4.4.180? There were two subsequent fixes to this patch
in 4.4:

485d15db01ca ("kbuild: simplify ld-option implementation")
07d35512e494 ("x86/vdso: Pass --eh-frame-hdr to the linker")

> And, indeed, when I back this patch out of 4.4.178 proper, the above test
> passes again.
> 
> Please consider backing this patch out of linux-4.4.y, and from master, and from
> any other linux branch it has been backported to.
> 

So this is broken in mainline too?

> PS: In backing it out of 4.4.178, I first backed out
> 
>    7c45b45fd6e928c9ce275c32f6fa98d317e6f5ee
>    
> This is a follow-on vdso patch which collides with the
> patch we are interested in removing.  As it claims to be
> only removing redundant code, it probably should never
> have been backported in the first place.

While it is redundant for ld.bfd, it causes a build failure with the
release version of ld.lld:

https://github.com/ClangBuiltLinux/linux/issues/31

Cheers,
Nathan