Re: [PATCH v4] riscv: fix oops caused by irqsoff latency tracer

Changbin Du
2022-02-25T00:10:29Z

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

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