(2013/11/14 19:41), Petr Mladek wrote:
> We would like to use text_poke_bp in ftrace. It might be called also during
> boot when there is only one CPU and we do not need to sync the others.
>
> The check is must to have because there are also disabled interrupts during
> the boot. Then the call would cause a deadlock, see the warning in
> "smp_call_function_many", kernel/smp.c:371.
>
> The change is inspired by the code in arch/x86/kernel/ftrace.c.
Looks good for me :)
Reviewed-by: Masami Hiramatsu <masami.hiramatsu...@hitachi.com>
>
> Signed-off-by: Petr Mladek <pmla...@suse.cz>
> ---
> arch/x86/kernel/alternative.c | 17 ++++++++++++++---
> 1 file changed, 14 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 2aebe54..125fb16 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -603,6 +603,17 @@ static void do_sync_core(void *info)
> sync_core();
> }
>
> +static void run_sync(void)
> +{
> + /*
> + * We do not need to sync other cores during boot when there is only one
> + * CPU enabled. In fact, we must not because there are also disabled
> + * interrupts. The call would fail because of a potential deadlock.
> + */
> + if (num_online_cpus() != 1)
> + on_each_cpu(do_sync_core, NULL, 1);
> +}
> +
> static bool bp_patching_in_progress;
> static void *bp_int3_handler, *bp_int3_addr;
>
> @@ -665,7 +676,7 @@ int text_poke_bp(void *addr, const void *opcode, size_t
> len, void *handler)
> if (unlikely(ret))
> goto fail;
>
> - on_each_cpu(do_sync_core, NULL, 1);
> + run_sync();
>
> if (len - sizeof(int3) > 0) {
> /* patch all but the first byte */
> @@ -678,14 +689,14 @@ int text_poke_bp(void *addr, const void *opcode, size_t
> len, void *handler)
> * not necessary and we'd be safe even without it. But
> * better safe than sorry (plus there's not only Intel).
> */
> - on_each_cpu(do_sync_core, NULL, 1);
> + run_sync();
> }
>
> /* patch the first byte */
> ret = text_poke(addr, opcode, sizeof(int3));
> BUG_ON(ret);
>
> - on_each_cpu(do_sync_core, NULL, 1);
> + run_sync();
>
> fail:
> bp_patching_in_progress = false;
>
--
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu...@hitachi.com
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