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

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Message-ID: <20190607010128.GB24007@zipoli.concurrent-rt.com>
Date:   Fri, 7 Jun 2019 01:01:36 +0000
From:   Joe Korty <Joe.Korty@...current-rt.com>
To:     Nathan Chancellor <natechancellor@...il.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" 
        <clang-built-linux@...glegroups.com>
Subject: Re: [BUG 4.4.178] x86_64 compat mode futexes broken

On Thu, Jun 06, 2019 at 04:11:30PM -0700, Nathan Chancellor wrote:
> 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:

Hi Nathan,
I started with 4.4.179-rt181 and worked backwards from there.  Per your
suggestion, I tried 4.4.180 and it does work properly.

Thanks,
Joe




> 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