linux-kernel - Re: [PATCH] powerpc/tools: drop `-o pipefail` in gcc check scripts

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Message-ID: <0ab92ae3-674f-445e-883c-0e511add85d2@redhat.com>
Date: Thu, 28 Aug 2025 09:32:18 -0400
From: Joe Lawrence <joe.lawrence@...hat.com>
To: Jan Stancek <jstancek@...hat.com>, maddy@...ux.ibm.com,
 mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org
Cc: npiggin@...il.com, christophe.leroy@...roup.eu,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/tools: drop `-o pipefail` in gcc check scripts

On 8/26/25 5:54 AM, Jan Stancek wrote:
> We've been observing rare non-deterministic kconfig failures during
> olddefconfig, where ARCH_USING_PATCHABLE_FUNCTION_ENTRY was getting
> disabled and with it number of other config options that depend on it.
> 
> The reason is that gcc-check-fpatchable-function-entry.sh can fail
> if `grep -q` (or scripts/dummy-tools/gcc) is fast enough to exit while
> there is still someone writing on other side of pipe. `pipefail`
> propagates that error up to kconfig.
> 
> This can be seen for example with:
>   # (set -e; set -o pipefail; yes | grep -q y); echo $?
>   141
> 
> or by running the actual check script in loop extensively:
>   ----------------------------- 8< -------------------------------
>   function kconfig()
>   {
>     for i in `seq 1 100`; do
>       arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh \
>         ./scripts/dummy-tools/gcc -mlittle-endian \
>         || { echo "Oops"; exit 1; }
>     done
>   }
> 
>   for ((i=0; i<$(nproc); i++)); do kconfig & done
>   wait; echo "Done"
>   ----------------------------- >8 -------------------------------
> 
> Fixes: 0f71dcfb4aef ("powerpc/ftrace: Add support for -fpatchable-function-entry")
> Fixes: b71c9ffb1405 ("powerpc: Add arch/powerpc/tools directory")
> Signed-off-by: Jan Stancek <jstancek@...hat.com>
> ---
>  arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh | 1 -
>  arch/powerpc/tools/gcc-check-mprofile-kernel.sh           | 1 -
>  2 files changed, 2 deletions(-)
> 
> diff --git a/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh b/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh
> index 06706903503b..baed467a016b 100755
> --- a/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh
> +++ b/arch/powerpc/tools/gcc-check-fpatchable-function-entry.sh
> @@ -2,7 +2,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  set -e
> -set -o pipefail
>  
>  # To debug, uncomment the following line
>  # set -x
> diff --git a/arch/powerpc/tools/gcc-check-mprofile-kernel.sh b/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
> index 73e331e7660e..6193b0ed0c77 100755
> --- a/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
> +++ b/arch/powerpc/tools/gcc-check-mprofile-kernel.sh
> @@ -2,7 +2,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
>  set -e
> -set -o pipefail
>  
>  # To debug, uncomment the following line
>  # set -x

Acked-by: Joe Lawrence <joe.lawrence@...hat.com>

This bug manifests when automated scripts expect to run a kernel build
after `make olddefconfig`.  I reported this to Jan when I found that
kpatch-build [1] instances were hanging (expecting to hear from a user
that would never answer :(

[1] https://github.com/dynup/kpatch/blob/master/kpatch-build/kpatch-build
-- 
Joe