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SubjectRe: [PATCH 3/3] arm64: ftrace: add cond_resched() to func ftrace_make_(call|nop)
On Fri, 30 Nov 2018 16:09:56 +0100
Anders Roxell <anders.roxell@linaro.org> wrote:

> Both of those functions end up calling ftrace_modify_code(), which is
> expensive because it changes the page tables and flush caches.
> Microseconds add up because this is called in a loop for each dyn_ftrace
> record, and this triggers the softlockup watchdog unless we let it sleep
> occasionally.
> Rework so that we call cond_resched() before going into the
> ftrace_modify_code() function.
>
> Co-developed-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Anders Roxell <anders.roxell@linaro.org>

I'm fine with this patch, but I'm not placing an ack on this patch
just because I don't know the repercussions of such a change. I'll let
you folks take full responsibility ;-)

-- Steve


> ---
> arch/arm64/kernel/ftrace.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
> index de1a397d2d3f..9da38da58df7 100644
> --- a/arch/arm64/kernel/ftrace.c
> +++ b/arch/arm64/kernel/ftrace.c
> @@ -130,6 +130,11 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> old = aarch64_insn_gen_nop();
> new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
>
> + /* This function can take a long time when sanitizers are enabled, so
> + * lets make sure we allow RCU processing.
> + */
> + cond_resched();
> +
> return ftrace_modify_code(pc, old, new, true);
> }
>
> @@ -188,6 +193,11 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
>
> new = aarch64_insn_gen_nop();
>
> + /* This function can take a long time when sanitizers are enabled, so
> + * lets make sure we allow RCU processing.
> + */
> + cond_resched();
> +
> return ftrace_modify_code(pc, old, new, validate);
> }
>

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