Message-ID: <1503022785.28554.101.camel@gmail.com>
Subject: Re: [PATCHv3] arm:kexec: have own crash_smp_send_stop() for crash
 dump for nonpanic cores
From: Hoeun Ryu <hoeun.ryu@gmail.com>
To: Russell King <linux@armlinux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Laura Abbott <labbott@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Date: Fri, 18 Aug 2017 11:19:45 +0900
In-Reply-To: <1502155416-5735-1-git-send-email-hoeun.ryu@gmail.com>
References: <1502155416-5735-1-git-send-email-hoeun.ryu@gmail.com>
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Hello, All.

Would you please review this patch ?
I haven't had any respond to this patch.

Thank you.

On Tue, 2017-08-08 at 10:22 +0900, Hoeun Ryu wrote:
>  Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
> version in panic path) introduced crash_smp_send_stop() which is a weak
> function and can be overriden by architecture codes to fix the side effect
> caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
> notifiers" option).
> 
>  ARM architecture uses the weak version function and the problem is that
> the weak function simply calls smp_send_stop() which makes other CPUs
> offline and takes away the chance to save crash information for nonpanic
> CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
> option is enabled.
> 
>  Calling smp_call_function(machine_crash_nonpanic_core, NULL, false) in
> the function is useless because all nonpanic CPUs are already offline by
> smp_send_stop() in this case and smp_call_function() only works against
> online CPUs.
> 
>  The result is that /proc/vmcore is not available with the error messages;
> "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".
> 
>  crash_smp_send_stop() is implemented for ARM architecture to fix this
> problem and the function (strong symbol version) saves crash information
> for nonpanic CPUs using smp_call_function() and machine_crash_shutdown()
> tries to save crash information for nonpanic CPUs only when
> crash_kexec_post_notifiers kernel option is disabled.
> 
>  We might be able to implement the function like arm64 or x86 using a
> dedicated IPI (let's say IPI_CPU_CRASH_STOP), but we cannot implement this
> function like that because of the lack of IPI slots. Please see the commit
> e7273ff4 : (ARM: 8488/1: Make IPI_CPU_BACKTRACE a "non-secure" SGI)
> 
> Signed-off-by: Hoeun Ryu <hoeun.ryu@gmail.com>
> ---
>  v3:
>    - remove 'WARN_ON(num_online_cpus() > 1)' in machine_crash_shutdown().
>      it's a false check for the case when crash_kexec_post_notifiers
>      kernel option is disabled.
>  v2:
>    - calling crash_smp_send_stop() in machine_crash_shutdown() for the case
>      when crash_kexec_post_notifiers kernel option is disabled.
>    - fix commit messages for it.
> 
>  arch/arm/kernel/machine_kexec.c | 40 +++++++++++++++++++++++++++++-----------
>  1 file changed, 29 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
> index fe1419e..82ef7c7 100644
> --- a/arch/arm/kernel/machine_kexec.c
> +++ b/arch/arm/kernel/machine_kexec.c
> @@ -94,6 +94,34 @@ void machine_crash_nonpanic_core(void *unused)
>  		cpu_relax();
>  }
>  
> +void crash_smp_send_stop(void)
> +{
> +	static int cpus_stopped;
> +	unsigned long msecs;
> +
> +	/*
> +	 * This function can be called twice in panic path, but obviously
> +	 * we execute this only once.
> +	 */
> +	if (cpus_stopped)
> +		return;
> +
> +	cpus_stopped = 1;
> +
> +	if (num_online_cpus() == 1)
> +		return;
> +
> +	atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
> +	smp_call_function(machine_crash_nonpanic_core, NULL, false);
> +	msecs = 1000; /* Wait at most a second for the other cpus to stop */
> +	while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
> +		mdelay(1);
> +		msecs--;
> +	}
> +	if (atomic_read(&waiting_for_crash_ipi) > 0)
> +		pr_warn("Non-crashing CPUs did not react to IPI\n");
> +}
> +
>  static void machine_kexec_mask_interrupts(void)
>  {
>  	unsigned int i;
> @@ -119,19 +147,9 @@ static void machine_kexec_mask_interrupts(void)
>  
>  void machine_crash_shutdown(struct pt_regs *regs)
>  {
> -	unsigned long msecs;
> -
>  	local_irq_disable();
>  
> -	atomic_set(&waiting_for_crash_ipi, num_online_cpus() - 1);
> -	smp_call_function(machine_crash_nonpanic_core, NULL, false);
> -	msecs = 1000; /* Wait at most a second for the other cpus to stop */
> -	while ((atomic_read(&waiting_for_crash_ipi) > 0) && msecs) {
> -		mdelay(1);
> -		msecs--;
> -	}
> -	if (atomic_read(&waiting_for_crash_ipi) > 0)
> -		pr_warn("Non-crashing CPUs did not react to IPI\n");
> +	crash_smp_send_stop();
>  
>  	crash_save_cpu(regs, smp_processor_id());
>  	machine_kexec_mask_interrupts();