Re: [PATCH 1/2] ftrace: Allow ftrace_replace_code() to be schedulable

[Anders Roxell]

On Wed, 5 Dec 2018 at 19:33, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx>
>
> The function ftrace_replace_code() is the ftrace engine that does the
> work to modify all the nops into the calls to the function callback in
> all the functions being traced.
>
> The generic version which is normally called from stop machine, but an
> architecture can implement a non stop machine version and still use the
> generic ftrace_replace_code(). When an architecture does this,
> ftrace_replace_code() may be called from a schedulable context, where
> it can allow the code to be preemptible, and schedule out.
>
> In order to allow an architecture to make ftrace_replace_code()
> schedulable, a new command flag is added called:
>
>  FTRACE_SCHEDULABLE
>
> Which can be or'd to the command that is passed to
> ftrace_modify_all_code() that calls ftrace_replace_code() and will have
> it call cond_resched() in the loop that modifies the nops into the
> calls to the ftrace trampolines.
>
> Link: http://lkml.kernel.org/r/20181204192903.8193-1-anders.roxell@xxxxxxxxxx
>
> Reported-by: Anders Roxell <anders.roxell@xxxxxxxxxx>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>

Tested-by: Anders Roxell <anders.roxell@xxxxxxxxxx>

Cheers,
Anders

> ---
>  include/linux/ftrace.h |  1 +
>  kernel/trace/ftrace.c  | 19 ++++++++++++++++---
>  2 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index dd16e8218db3..c281b16baef9 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -389,6 +389,7 @@ enum {
>         FTRACE_UPDATE_TRACE_FUNC        = (1 << 2),
>         FTRACE_START_FUNC_RET           = (1 << 3),
>         FTRACE_STOP_FUNC_RET            = (1 << 4),
> +       FTRACE_SCHEDULABLE              = (1 << 5),
>  };
>
>  /*
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 77734451cb05..74fdcacba514 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -77,6 +77,11 @@
>  #define ASSIGN_OPS_HASH(opsname, val)
>  #endif
>
> +enum {
> +       FTRACE_MODIFY_ENABLE_FL         = (1 << 0),
> +       FTRACE_MODIFY_SCHEDULABLE_FL    = (1 << 1),
> +};
> +
>  static struct ftrace_ops ftrace_list_end __read_mostly = {
>         .func           = ftrace_stub,
>         .flags          = FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_STUB,
> @@ -2415,10 +2420,12 @@ __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
>         return -1; /* unknow ftrace bug */
>  }
>
> -void __weak ftrace_replace_code(int enable)
> +void __weak ftrace_replace_code(int mod_flags)
>  {
>         struct dyn_ftrace *rec;
>         struct ftrace_page *pg;
> +       int enable = mod_flags & FTRACE_MODIFY_ENABLE_FL;
> +       int schedulable = mod_flags & FTRACE_MODIFY_SCHEDULABLE_FL;
>         int failed;
>
>         if (unlikely(ftrace_disabled))
> @@ -2435,6 +2442,8 @@ void __weak ftrace_replace_code(int enable)
>                         /* Stop processing */
>                         return;
>                 }
> +               if (schedulable)
> +                       cond_resched();
>         } while_for_each_ftrace_rec();
>  }
>
> @@ -2548,8 +2557,12 @@ int __weak ftrace_arch_code_modify_post_process(void)
>  void ftrace_modify_all_code(int command)
>  {
>         int update = command & FTRACE_UPDATE_TRACE_FUNC;
> +       int mod_flags = 0;
>         int err = 0;
>
> +       if (command & FTRACE_SCHEDULABLE)
> +               mod_flags = FTRACE_MODIFY_SCHEDULABLE_FL;
> +
>         /*
>          * If the ftrace_caller calls a ftrace_ops func directly,
>          * we need to make sure that it only traces functions it
> @@ -2567,9 +2580,9 @@ void ftrace_modify_all_code(int command)
>         }
>
>         if (command & FTRACE_UPDATE_CALLS)
> -               ftrace_replace_code(1);
> +               ftrace_replace_code(mod_flags | FTRACE_MODIFY_ENABLE_FL);
>         else if (command & FTRACE_DISABLE_CALLS)
> -               ftrace_replace_code(0);
> +               ftrace_replace_code(mod_flags);
>
>         if (update && ftrace_trace_function != ftrace_ops_list_func) {
>                 function_trace_op = set_function_trace_op;
> --
> 2.19.1
>
>