Messages in this thread | | | Date | Thu, 6 May 2021 09:20:00 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH] RISC-V: Don't check text_mutex during stop_machine |
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On Thu, 6 May 2021 00:10:41 -0700 Palmer Dabbelt <palmer@dabbelt.com> wrote:
> diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c > index 7f1e5203de88..da2405652f1d 100644 > --- a/arch/riscv/kernel/ftrace.c > +++ b/arch/riscv/kernel/ftrace.c > @@ -11,6 +11,8 @@ > #include <asm/cacheflush.h> > #include <asm/patch.h> > > +int riscv_ftrace_in_stop_machine; > + > #ifdef CONFIG_DYNAMIC_FTRACE > int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) > { > @@ -232,3 +234,16 @@ int ftrace_disable_ftrace_graph_caller(void) > } > #endif /* CONFIG_DYNAMIC_FTRACE */ > #endif /* CONFIG_FUNCTION_GRAPH_TRACER */ > + > +void arch_ftrace_update_code(int command) > +{ > + /* > + * The code sequences we use for ftrace can't be patched while the > + * kernel is running, so we need to use stop_machine() to modify them > + * for now. This doesn't play nice with text_mutex, we use this flag > + * to elide the check. > + */ > + riscv_ftrace_in_stop_machine = true; > + ftrace_run_stop_machine(command); > + riscv_ftrace_in_stop_machine = false; > +} > diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c > index 0b552873a577..7983dba477f0 100644
This would work, but my suggestion was to do it without having to add this arch function. Because the caller of this is:
static void ftrace_run_update_code(int command) { int ret;
ret = ftrace_arch_code_modify_prepare(); FTRACE_WARN_ON(ret); if (ret) return;
/* * By default we use stop_machine() to modify the code. * But archs can do what ever they want as long as it * is safe. The stop_machine() is the safest, but also * produces the most overhead. */ arch_ftrace_update_code(command);
ret = ftrace_arch_code_modify_post_process(); FTRACE_WARN_ON(ret); }
Where you already have two hooks that you use to take the text_mutex before calling arch_ftrace_update_code().
In RISC-V those are:
int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) { mutex_lock(&text_mutex); return 0; }
int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) { mutex_unlock(&text_mutex); return 0; }
Where all you have to do is change them to:
int ftrace_arch_code_modify_prepare(void) __acquires(&text_mutex) { mutex_lock(&text_mutex); riscv_ftrace_in_stop_machine = true; return 0; }
int ftrace_arch_code_modify_post_process(void) __releases(&text_mutex) { riscv_ftrace_in_stop_machine = false; mutex_unlock(&text_mutex); return 0; }
And you have the exact same affect. Those functions are only used before calling the stop machine code you have.
-- Steve
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