Re: [PATCH] stop_machine: Mark functions as notrace

[Guo Ren]

Hi Zong & Atish,

In our 2 harts c910 chip, we found:

echo function > /sys/kernel/debug/tracing/current_tracer
echo function_graph > /sys/kernel/debug/tracing/current_tracer
echo function > /sys/kernel/debug/tracing/current_tracer
echo function_graph > /sys/kernel/debug/tracing/current_tracer

Then one core halted at stop_machine_yield:
arch_cpu_idle () at arch/riscv/kernel/process.c:39
39              local_irq_enable();
(gdb) i th
  Id   Target Id         Frame
* 1    Thread 1 (CPU#0)  arch_cpu_idle () at arch/riscv/kernel/process.c:39
  2    Thread 2 (CPU#1)  stop_machine_yield
(cpumask=0xffffffe001371fa8 <__cpu_online_mask>) at
./arch/riscv/include/asm/vdso/processor.h:12
(gdb) thread 2
[Switching to thread 2 (Thread 2)]
#0  stop_machine_yield (cpumask=0xffffffe001371fa8
<__cpu_online_mask>) at ./arch/riscv/include/asm/vdso/processor.h:12
12              __asm__ __volatile__ ("div %0, %0, zero" : "=r" (dummy));

With your patch, it's solved. For this patch, I'll give:
Tested by: Guo Ren <guoren@xxxxxxxxxx>

But that's not enough, we still need:

diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
index 226ccce..12b8808 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -376,7 +376,7 @@ EXPORT_SYMBOL(sbi_send_ipi);
  *
  * Return: None
  */
-void sbi_remote_fence_i(const unsigned long *hart_mask)
+void notrace sbi_remote_fence_i(const unsigned long *hart_mask)
 {
        __sbi_rfence(SBI_EXT_RFENCE_REMOTE_FENCE_I,
                     hart_mask, 0, 0, 0, 0);
diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
index 400b945d..9467d987 100644
--- a/arch/riscv/mm/cacheflush.c
+++ b/arch/riscv/mm/cacheflush.c
@@ -9,12 +9,12 @@

 #include <asm/sbi.h>

-static void ipi_remote_fence_i(void *info)
+static void notrace ipi_remote_fence_i(void *info)
 {
        return local_flush_icache_all();
 }

-void flush_icache_all(void)
+void notrace flush_icache_all(void)
 {
        if (IS_ENABLED(CONFIG_RISCV_SBI))
                sbi_remote_fence_i(NULL);

Because:
(gdb) bt
#0  flush_icache_all () at arch/riscv/mm/cacheflush.c:20
#1  0xffffffe00020473a in patch_text_nosync (addr=<optimized out>, insns=
    <optimized out>, len=<optimized out>) at arch/riscv/kernel/patch.c:96
#2  0xffffffe000206792 in ftrace_make_call (rec=<optimized out>,
addr=<optimized out>) at arch/riscv/kernel/ftrace.c:109
#3  0xffffffe0002c9be4 in __ftrace_replace_code (rec=0xffffffe01ae40020, e
    nable=true) at kernel/trace/ftrace.c:2503
#4  0xffffffe0002ca092 in ftrace_replace_code (mod_flags=<optimized
    out>) at kernel/trace/ftrace.c:2530
#5  0xffffffe0002ca24a in ftrace_modify_all_code (command=9) at kernel
   /trace/ftrace.c:2677
#6  0xffffffe0002ca2ee in __ftrace_modify_code (data=<optimized out>) at
   kernel/trace/ftrace.c:2703
#7  0xffffffe0002c1390 in multi_cpu_stop (data=0x0) at kernel/stop_machin
   e.c:224
#8  0xffffffe0002c0fbe in cpu_stopper_thread (cpu=<optimized out>) at kern
   el/stop_machine.c:491
#9  0xffffffe0002343be in smpboot_thread_fn (data=0x0) at kernel/smpboot.
   c:165
#10 0xffffffe00022f894 in kthread (_create=0xffffffe01af13040) at kern
   el/kthread.c:292
#11 0xffffffe000201fac in handle_exception () at arch/riscv/kernel/entry.S:236

On Wed, Oct 21, 2020 at 3:38 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
>
> Like the commit cb9d7fd51d9f ("watchdog: Mark watchdog touch functions
> as notrace"), some architectures assume that the stopped CPUs don't make
> function calls to traceable functions when they are in the stopped
> state. For example, it causes unexpected kernel crashed when switching
> tracer on RISC-V.
>
> The following patches added calls to these two functions, fix it by
> adding the notrace annotations.
>
> Fixes: 4ecf0a43e729 ("processor: get rid of cpu_relax_yield")
> Fixes: 366237e7b083 ("stop_machine: Provide RCU quiescent state in
> multi_cpu_stop()")
>
> Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
> ---
>  kernel/rcu/tree.c     | 2 +-
>  kernel/stop_machine.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 06895ef85d69..2a52f42f64b6 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -409,7 +409,7 @@ bool rcu_eqs_special_set(int cpu)
>   *
>   * The caller must have disabled interrupts and must not be idle.
>   */
> -void rcu_momentary_dyntick_idle(void)
> +notrace void rcu_momentary_dyntick_idle(void)
>  {
>         int special;
>
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index 865bb0228ab6..890b79cf0e7c 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -178,7 +178,7 @@ static void ack_state(struct multi_stop_data *msdata)
>                 set_state(msdata, msdata->state + 1);
>  }
>
> -void __weak stop_machine_yield(const struct cpumask *cpumask)
> +notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
>  {
>         cpu_relax();
>  }
> --
> 2.28.0
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/