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Date:   Fri, 25 Feb 2022 08:10:00 +0800
From:   Changbin Du <changbin.du@gmail.com>
To:     Changbin Du <changbin.du@gmail.com>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4] riscv: fix oops caused by irqsoff latency tracer
Message-ID: <20220225001000.ccxaotz6v64ldlap@mail.google.com>
References: <20220213081845.9864-1-changbin.du@gmail.com>
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In-Reply-To: <20220213081845.9864-1-changbin.du@gmail.com>
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hello, kindly ping for review status. :)

On Sun, Feb 13, 2022 at 04:18:45PM +0800, Changbin Du wrote:
> The trace_hardirqs_{on,off}() require the caller to setup frame pointer
> properly. This because these two functions use macro 'CALLER_ADDR1' (aka.
> __builtin_return_address(1)) to acquire caller info. If the $fp is used
> for other purpose, the code generated this macro (as below) could trigger
> memory access fault.
> 
>    0xffffffff8011510e <+80>:    ld      a1,-16(s0)
>    0xffffffff80115112 <+84>:    ld      s2,-8(a1)  # <-- paging fault here
> 
> The oops message during booting if compiled with 'irqoff' tracer enabled:
> [    0.039615][    T0] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000f8
> [    0.041925][    T0] Oops [#1]
> [    0.042063][    T0] Modules linked in:
> [    0.042864][    T0] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.17.0-rc1-00233-g9a20c48d1ed2 #29
> [    0.043568][    T0] Hardware name: riscv-virtio,qemu (DT)
> [    0.044343][    T0] epc : trace_hardirqs_on+0x56/0xe2
> [    0.044601][    T0]  ra : restore_all+0x12/0x6e
> [    0.044721][    T0] epc : ffffffff80126a5c ra : ffffffff80003b94 sp : ffffffff81403db0
> [    0.044801][    T0]  gp : ffffffff8163acd8 tp : ffffffff81414880 t0 : 0000000000000020
> [    0.044882][    T0]  t1 : 0098968000000000 t2 : 0000000000000000 s0 : ffffffff81403de0
> [    0.044967][    T0]  s1 : 0000000000000000 a0 : 0000000000000001 a1 : 0000000000000100
> [    0.045046][    T0]  a2 : 0000000000000000 a3 : 0000000000000000 a4 : 0000000000000000
> [    0.045124][    T0]  a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000054494d45
> [    0.045210][    T0]  s2 : ffffffff80003b94 s3 : ffffffff81a8f1b0 s4 : ffffffff80e27b50
> [    0.045289][    T0]  s5 : ffffffff81414880 s6 : ffffffff8160fa00 s7 : 00000000800120e8
> [    0.045389][    T0]  s8 : 0000000080013100 s9 : 000000000000007f s10: 0000000000000000
> [    0.045474][    T0]  s11: 0000000000000000 t3 : 7fffffffffffffff t4 : 0000000000000000
> [    0.045548][    T0]  t5 : 0000000000000000 t6 : ffffffff814aa368
> [    0.045620][    T0] status: 0000000200000100 badaddr: 00000000000000f8 cause: 000000000000000d
> [    0.046402][    T0] [<ffffffff80003b94>] restore_all+0x12/0x6e
> 
> This because the $fp(aka. $s0) register is not used as frame pointer in the
> assembly entry code.
> 
> 	resume_kernel:
> 		REG_L s0, TASK_TI_PREEMPT_COUNT(tp)
> 		bnez s0, restore_all
> 		REG_L s0, TASK_TI_FLAGS(tp)
>                 andi s0, s0, _TIF_NEED_RESCHED
>                 beqz s0, restore_all
>                 call preempt_schedule_irq
>                 j restore_all
> 
> To fix above issue, here we add one extra level wrapper for function
> trace_hardirqs_{on,off}() so they can be safely called by low level entry
> code.
> 
> Signed-off-by: Changbin Du <changbin.du@gmail.com>
> 
> ---
> v4: update explanation.
> v3: fix warning reported by documentation system.
> v2: fix compile warning.
> ---
>  arch/riscv/kernel/Makefile    |  2 ++
>  arch/riscv/kernel/entry.S     | 10 +++++-----
>  arch/riscv/kernel/trace_irq.c | 27 +++++++++++++++++++++++++++
>  arch/riscv/kernel/trace_irq.h | 11 +++++++++++
>  4 files changed, 45 insertions(+), 5 deletions(-)
>  create mode 100644 arch/riscv/kernel/trace_irq.c
>  create mode 100644 arch/riscv/kernel/trace_irq.h
> 
> diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
> index 612556faa527..ffc87e76b1dd 100644
> --- a/arch/riscv/kernel/Makefile
> +++ b/arch/riscv/kernel/Makefile
> @@ -51,6 +51,8 @@ obj-$(CONFIG_MODULE_SECTIONS)	+= module-sections.o
>  obj-$(CONFIG_FUNCTION_TRACER)	+= mcount.o ftrace.o
>  obj-$(CONFIG_DYNAMIC_FTRACE)	+= mcount-dyn.o
>  
> +obj-$(CONFIG_TRACE_IRQFLAGS)	+= trace_irq.o
> +
>  obj-$(CONFIG_RISCV_BASE_PMU)	+= perf_event.o
>  obj-$(CONFIG_PERF_EVENTS)	+= perf_callchain.o
>  obj-$(CONFIG_HAVE_PERF_REGS)	+= perf_regs.o
> diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
> index ed29e9c8f660..d6a46ed0bf05 100644
> --- a/arch/riscv/kernel/entry.S
> +++ b/arch/riscv/kernel/entry.S
> @@ -108,7 +108,7 @@ _save_context:
>  .option pop
>  
>  #ifdef CONFIG_TRACE_IRQFLAGS
> -	call trace_hardirqs_off
> +	call __trace_hardirqs_off
>  #endif
>  
>  #ifdef CONFIG_CONTEXT_TRACKING
> @@ -143,7 +143,7 @@ skip_context_tracking:
>  	li t0, EXC_BREAKPOINT
>  	beq s4, t0, 1f
>  #ifdef CONFIG_TRACE_IRQFLAGS
> -	call trace_hardirqs_on
> +	call __trace_hardirqs_on
>  #endif
>  	csrs CSR_STATUS, SR_IE
>  
> @@ -234,7 +234,7 @@ ret_from_exception:
>  	REG_L s0, PT_STATUS(sp)
>  	csrc CSR_STATUS, SR_IE
>  #ifdef CONFIG_TRACE_IRQFLAGS
> -	call trace_hardirqs_off
> +	call __trace_hardirqs_off
>  #endif
>  #ifdef CONFIG_RISCV_M_MODE
>  	/* the MPP value is too large to be used as an immediate arg for addi */
> @@ -270,10 +270,10 @@ restore_all:
>  	REG_L s1, PT_STATUS(sp)
>  	andi t0, s1, SR_PIE
>  	beqz t0, 1f
> -	call trace_hardirqs_on
> +	call __trace_hardirqs_on
>  	j 2f
>  1:
> -	call trace_hardirqs_off
> +	call __trace_hardirqs_off
>  2:
>  #endif
>  	REG_L a0, PT_STATUS(sp)
> diff --git a/arch/riscv/kernel/trace_irq.c b/arch/riscv/kernel/trace_irq.c
> new file mode 100644
> index 000000000000..095ac976d7da
> --- /dev/null
> +++ b/arch/riscv/kernel/trace_irq.c
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Changbin Du <changbin.du@gmail.com>
> + */
> +
> +#include <linux/irqflags.h>
> +#include <linux/kprobes.h>
> +#include "trace_irq.h"
> +
> +/*
> + * trace_hardirqs_on/off require the caller to setup frame pointer properly.
> + * Otherwise, CALLER_ADDR1 might trigger an pagging exception in kernel.
> + * Here we add one extra level so they can be safely called by low
> + * level entry code which $fp is used for other purpose.
> + */
> +
> +void __trace_hardirqs_on(void)
> +{
> +	trace_hardirqs_on();
> +}
> +NOKPROBE_SYMBOL(__trace_hardirqs_on);
> +
> +void __trace_hardirqs_off(void)
> +{
> +	trace_hardirqs_off();
> +}
> +NOKPROBE_SYMBOL(__trace_hardirqs_off);
> diff --git a/arch/riscv/kernel/trace_irq.h b/arch/riscv/kernel/trace_irq.h
> new file mode 100644
> index 000000000000..99fe67377e5e
> --- /dev/null
> +++ b/arch/riscv/kernel/trace_irq.h
> @@ -0,0 +1,11 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2022 Changbin Du <changbin.du@gmail.com>
> + */
> +#ifndef __TRACE_IRQ_H
> +#define __TRACE_IRQ_H
> +
> +void __trace_hardirqs_on(void);
> +void __trace_hardirqs_off(void);
> +
> +#endif /* __TRACE_IRQ_H */
> -- 
> 2.32.0
> 

-- 
Cheers,
Changbin Du