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Date:   Fri, 3 Jan 2020 16:16:07 -0800 (PST)
From:   Paul Walmsley <paul.walmsley@sifive.com>
To:     Zong Li <zong.li@sifive.com>
cc:     palmer@dabbelt.com, rostedt@goodmis.org, anup@brainfault.org,
        linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org
Subject: Re: [PATCH 2/2] clocksource/drivers/riscv: add notrace to
 riscv_sched_clock
In-Reply-To: <20191223084614.67126-3-zong.li@sifive.com>
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References: <20191223084614.67126-1-zong.li@sifive.com> <20191223084614.67126-3-zong.li@sifive.com>
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On Mon, 23 Dec 2019, Zong Li wrote:

> When enabling ftrace graph tracer, it gets the tracing clock in
> ftrace_push_return_trace. Eventually, it invokes the riscv_sched_clock to
> get the clock. If add mcount instrument in riscv_sched_clock, it will
> call ftrace_push_return_trace and cause infinite loop.
> 
> The result of failure as follow:
> 
> command: echo function_graph >current_tracer
> [   46.176787] Unable to handle kernel paging request at virtual address ffffffe04fb38c48
> [   46.177309] Oops [#1]
> [   46.177478] Modules linked in:
> [   46.177770] CPU: 0 PID: 256 Comm: $d Not tainted 5.5.0-rc1 #47
> [   46.177981] epc: ffffffe00035e59a ra : ffffffe00035e57e sp : ffffffe03a7569b0
> [   46.178216]  gp : ffffffe000d29b90 tp : ffffffe03a756180 t0 : ffffffe03a756968
> [   46.178430]  t1 : ffffffe00087f408 t2 : ffffffe03a7569a0 s0 : ffffffe03a7569f0
> [   46.178643]  s1 : ffffffe00087f408 a0 : 0000000ac054cda4 a1 : 000000000087f411
> [   46.178856]  a2 : 0000000ac054cda4 a3 : 0000000000373ca0 a4 : ffffffe04fb38c48
> [   46.179099]  a5 : 00000000153e22a8 a6 : 00000000005522ff a7 : 0000000000000005
> [   46.179338]  s2 : ffffffe03a756a90 s3 : ffffffe00032811c s4 : ffffffe03a756a58
> [   46.179570]  s5 : ffffffe000d29fe0 s6 : 0000000000000001 s7 : 0000000000000003
> [   46.179809]  s8 : 0000000000000003 s9 : 0000000000000002 s10: 0000000000000004
> [   46.180053]  s11: 0000000000000000 t3 : 0000003fc815749c t4 : 00000000000efc90
> [   46.180293]  t5 : ffffffe000d29658 t6 : 0000000000040000
> [   46.180482] status: 0000000000000100 badaddr: ffffffe04fb38c48 cause: 000000000000000f
> 
> Signed-off-by: Zong Li <zong.li@sifive.com>

Thanks; below is what's been queued for v5.5-rc.


- Paul


From: Zong Li <zong.li@sifive.com>
Date: Mon, 23 Dec 2019 16:46:14 +0800
Subject: [PATCH 1/2] clocksource/drivers/riscv: add notrace to
 riscv_sched_clock

When enabling ftrace graph tracer, it gets the tracing clock in
ftrace_push_return_trace().  Eventually, it invokes riscv_sched_clock()
to get the clock value.  If riscv_sched_clock() isn't marked with
'notrace', it will call ftrace_push_return_trace() and cause infinite
loop.

The result of failure as follow:

command: echo function_graph >current_tracer
[   46.176787] Unable to handle kernel paging request at virtual address ffffffe04fb38c48
[   46.177309] Oops [#1]
[   46.177478] Modules linked in:
[   46.177770] CPU: 0 PID: 256 Comm: $d Not tainted 5.5.0-rc1 #47
[   46.177981] epc: ffffffe00035e59a ra : ffffffe00035e57e sp : ffffffe03a7569b0
[   46.178216]  gp : ffffffe000d29b90 tp : ffffffe03a756180 t0 : ffffffe03a756968
[   46.178430]  t1 : ffffffe00087f408 t2 : ffffffe03a7569a0 s0 : ffffffe03a7569f0
[   46.178643]  s1 : ffffffe00087f408 a0 : 0000000ac054cda4 a1 : 000000000087f411
[   46.178856]  a2 : 0000000ac054cda4 a3 : 0000000000373ca0 a4 : ffffffe04fb38c48
[   46.179099]  a5 : 00000000153e22a8 a6 : 00000000005522ff a7 : 0000000000000005
[   46.179338]  s2 : ffffffe03a756a90 s3 : ffffffe00032811c s4 : ffffffe03a756a58
[   46.179570]  s5 : ffffffe000d29fe0 s6 : 0000000000000001 s7 : 0000000000000003
[   46.179809]  s8 : 0000000000000003 s9 : 0000000000000002 s10: 0000000000000004
[   46.180053]  s11: 0000000000000000 t3 : 0000003fc815749c t4 : 00000000000efc90
[   46.180293]  t5 : ffffffe000d29658 t6 : 0000000000040000
[   46.180482] status: 0000000000000100 badaddr: ffffffe04fb38c48 cause: 000000000000000f

Signed-off-by: Zong Li <zong.li@sifive.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
[paul.walmsley@sifive.com: cleaned up patch description]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
---
 drivers/clocksource/timer-riscv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/clocksource/timer-riscv.c b/drivers/clocksource/timer-riscv.c
index 4e54856ce2a5..c4f15c4068c0 100644
--- a/drivers/clocksource/timer-riscv.c
+++ b/drivers/clocksource/timer-riscv.c
@@ -56,7 +56,7 @@ static unsigned long long riscv_clocksource_rdtime(struct clocksource *cs)
 	return get_cycles64();
 }
 
-static u64 riscv_sched_clock(void)
+static u64 notrace riscv_sched_clock(void)
 {
 	return get_cycles64();
 }
-- 
2.24.0