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@xxxxxxxxxx>
>
> [ 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@xxxxxxxxxx>
> Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
> ---
> 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
>
