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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Mikulas Patocka <mpatocka@redhat.com>,
        Will Deacon <will.deacon@arm.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.18 032/136] arm64: fix infinite stacktrace
Thread-Topic: [PATCH AUTOSEL 4.18 032/136] arm64: fix infinite stacktrace
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Date:   Mon, 17 Sep 2018 03:00:32 +0000
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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=3D952/1/4611686018427387904 sof=
tirq=3D1462/1462 fqs=3D355
[  908.797692]  2-...!: (1 GPs behind) idle=3Df42/1/4611686018427387904 sof=
tirq=3D1550/1551 fqs=3D355
[  908.799189]  (detected by 0, t=3D2109 jiffies, g=3D130, c=3D129, q=3D235=
)
[  908.800284] Task dump for CPU 1:
[  908.800871] kworker/1:1     R  running task        0    32      2 0x0000=
0022
[  908.802127] Workqueue: writecache-writeabck writecache_writeback [dm_wri=
tecache]
[  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 =3D READ_ONCE_NOCHECK(*(unsigned long *)(fp));
 	frame->pc =3D READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
=20
+	if (frame->fp <=3D fp)
+		return -EINVAL;
+
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 	if (tsk->ret_stack &&
 			(frame->pc =3D=3D (unsigned long)return_to_handler)) {
--=20
2.17.1