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Date:   Tue, 18 Sep 2018 06:55:34 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@redhat.com>
To:     Sasha Levin <Alexander.Levin@microsoft.com>
cc:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH AUTOSEL 4.18 032/136] arm64: fix infinite stacktrace
In-Reply-To: <20180917030006.245495-32-alexander.levin@microsoft.com>
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References: <20180917030006.245495-1-alexander.levin@microsoft.com> <20180917030006.245495-32-alexander.levin@microsoft.com>
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This patch is not correct, because the stacktrace is supposed to work 
around discontiguous interrupt stacks.

You should replace 'frame->fp <= fp' with 'frame->fp == fp'.

Mikulas


On Mon, 17 Sep 2018, Sasha Levin wrote:

> From: Mikulas Patocka <mpatocka@redhat.com>
> 
> [ Upstream commit 7e7df71fd57ff2894d96abb0080922bf39460a79 ]
> 
> I've got this infinite stacktrace when debugging another problem:
> [  908.795225] INFO: rcu_preempt detected stalls on CPUs/tasks:
> [  908.796176]  1-...!: (1 GPs behind) idle=952/1/4611686018427387904 softirq=1462/1462 fqs=355
> [  908.797692]  2-...!: (1 GPs behind) idle=f42/1/4611686018427387904 softirq=1550/1551 fqs=355
> [  908.799189]  (detected by 0, t=2109 jiffies, g=130, c=129, q=235)
> [  908.800284] Task dump for CPU 1:
> [  908.800871] kworker/1:1     R  running task        0    32      2 0x00000022
> [  908.802127] Workqueue: writecache-writeabck writecache_writeback [dm_writecache]
> [  908.820285] Call trace:
> [  908.824785]  __switch_to+0x68/0x90
> [  908.837661]  0xfffffe00603afd90
> [  908.844119]  0xfffffe00603afd90
> [  908.850091]  0xfffffe00603afd90
> [  908.854285]  0xfffffe00603afd90
> [  908.863538]  0xfffffe00603afd90
> [  908.865523]  0xfffffe00603afd90
> 
> The machine just locked up and kept on printing the same line over and
> over again. This patch fixes it.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> ---
>  arch/arm64/kernel/stacktrace.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c
> index d5718a060672..e160ca123da3 100644
> --- a/arch/arm64/kernel/stacktrace.c
> +++ b/arch/arm64/kernel/stacktrace.c
> @@ -56,6 +56,9 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
>  	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
>  	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
>  
> +	if (frame->fp <= fp)
> +		return -EINVAL;
> +
>  #ifdef CONFIG_FUNCTION_GRAPH_TRACER
>  	if (tsk->ret_stack &&
>  			(frame->pc == (unsigned long)return_to_handler)) {
> -- 
> 2.17.1
>