linux-kernel - Re: [PATCH RESEND v2] kexec/crash: no crash update when kexec in progress

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Message-ID: <ZuGnH5R+FOC481V3@MiWiFi-R3L-srv>
Date: Wed, 11 Sep 2024 22:20:15 +0800
From: Baoquan He <bhe@...hat.com>
To: Sourabh Jain <sourabhjain@...ux.ibm.com>
Cc: akpm@...ux-foundation.org, Hari Bathini <hbathini@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>, kexec@...ts.infradead.org,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	x86@...nel.org, Sachin P Bappalige <sachinpb@...ux.vnet.ibm.com>
Subject: Re: [PATCH RESEND v2] kexec/crash: no crash update when kexec in
 progress

On 09/11/24 at 04:51pm, Sourabh Jain wrote:
> The following errors are observed when kexec is done with SMT=off on
> powerpc.
> 
> [  358.458385] Removing IBM Power 842 compression device
> [  374.795734] kexec_core: Starting new kernel
> [  374.795748] kexec: Waking offline cpu 1.
> [  374.875695] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> [  374.935833] kexec: Waking offline cpu 2.
> [  375.015664] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> snip..
> [  375.515823] kexec: Waking offline cpu 6.
> [  375.635667] crash hp: kexec_trylock() failed, elfcorehdr may be inaccurate
> [  375.695836] kexec: Waking offline cpu 7.
> 
> To avoid kexec kernel boot failure on PowerPC, all the present CPUs that
> are offline are brought online during kexec. For more information, refer
> to commit e8e5c2155b00 ("powerpc/kexec: Fix orphaned offline CPUs across
> kexec"). Bringing the CPUs online triggers the crash hotplug handler,
> crash_handle_hotplug_event(), to update the kdump image. Since the
> system is on the kexec kernel boot path and the kexec lock is held, the
> crash_handle_hotplug_event() function fails to acquire the same lock to
> update the kdump image, resulting in the error messages mentioned above.
> 
> To fix this, return from crash_handle_hotplug_event() without printing
> the error message if kexec is in progress.
> 
> The same applies to the crash_check_hotplug_support() function. Return
> 0 if kexec is in progress because kernel is not in a position to update
> the kdump image.

LGTM, thanks.

Acked-by: Baoquan he <bhe@...hat.com>

> 
> Cc: Hari Bathini <hbathini@...ux.ibm.com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: kexec@...ts.infradead.org
> Cc: linuxppc-dev@...ts.ozlabs.org
> Cc: linux-kernel@...r.kernel.org
> Cc: x86@...nel.org
> Reported-by: Sachin P Bappalige <sachinpb@...ux.vnet.ibm.com>
> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> ---
> Changelog:
> 
> Since v1:
>  - Keep the kexec_in_progress check within kexec_trylock() - Baoquan He
>  - Include the reason why PowerPC brings offline CPUs online
>    during the kexec kernel boot path - Baoquan He
>  - Rebased on top of #next-20240910 to avoid conflict with the patch below
>    https://lore.kernel.org/all/20240812041651.703156-1-sourabhjain@linux.ibm.com/T/#u
> 
> V2 RESEND:
>  - Update linuxppc-dev mailing list address
> ---
>  kernel/crash_core.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index c1048893f4b6..078fe5bc5a74 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -505,7 +505,8 @@ int crash_check_hotplug_support(void)
>  	crash_hotplug_lock();
>  	/* Obtain lock while reading crash information */
>  	if (!kexec_trylock()) {
> -		pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
> +		if (!kexec_in_progress)
> +			pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
>  		crash_hotplug_unlock();
>  		return 0;
>  	}
> @@ -547,7 +548,8 @@ static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu,
>  	crash_hotplug_lock();
>  	/* Obtain lock while changing crash information */
>  	if (!kexec_trylock()) {
> -		pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
> +		if (!kexec_in_progress)
> +			pr_info("kexec_trylock() failed, kdump image may be inaccurate\n");
>  		crash_hotplug_unlock();
>  		return;
>  	}
> -- 
> 2.46.0
>