Re: [PATCH v2] arm64: Return early when break handler is found on linked-list
From: Will Deacon
Date: Thu Oct 24 2024 - 10:50:58 EST
On Thu, Oct 24, 2024 at 03:41:20AM +0000, Liao Chang wrote:
> The search for breakpoint handlers iterate through the entire
> linked list. Given that all registered hook has a valid fn field, and no
> registered hooks share the same mask and imm. This commit optimize the
> efficiency slightly by returning early as a matching handler is found.
>
> v2->v1:
> Remove all WARN_ON(!hook->fn) in v1 as Will suggested.
nit: Changelogs like ^^^ should go after the '---' line, otherwise they
end up in the git history.
> Signed-off-by: Liao Chang <liaochang1@xxxxxxxxxx>
> ---
> arch/arm64/kernel/debug-monitors.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
> index c60a4a90c6a5..58f047de3e1c 100644
> --- a/arch/arm64/kernel/debug-monitors.c
> +++ b/arch/arm64/kernel/debug-monitors.c
> @@ -303,7 +303,6 @@ static int call_break_hook(struct pt_regs *regs, unsigned long esr)
> {
> struct break_hook *hook;
> struct list_head *list;
> - int (*fn)(struct pt_regs *regs, unsigned long esr) = NULL;
>
> list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
>
> @@ -313,10 +312,10 @@ static int call_break_hook(struct pt_regs *regs, unsigned long esr)
> */
> list_for_each_entry_rcu(hook, list, node) {
> if ((esr_brk_comment(esr) & ~hook->mask) == hook->imm)
> - fn = hook->fn;
> + return hook->fn(regs, esr);
> }
>
> - return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
> + return DBG_HOOK_ERROR;
> }
> NOKPROBE_SYMBOL(call_break_hook);
Acked-by: Will Deacon <will@xxxxxxxxxx>
I assume Catalin will pick this one up (but he'll need to tweak the
commit message as per my comment above).
Will