Messages in this thread | | | Date | Mon, 22 Jul 2019 05:07:58 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH v2 4/4] arm64: Remove unneeded rcu_read_lock from debug handlers |
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On Mon, Jul 22, 2019 at 04:49:11PM +0900, Masami Hiramatsu wrote: > Remove rcu_read_lock()/rcu_read_unlock() from debug exception > handlers since we are sure those are not preemptible and > interrupts are off. > > Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org> > Cc: Paul E. McKenney <paulmck@linux.ibm.com>
From an RCU viewpoint:
Acked-by: Paul E. McKenney <paulmck@linux.ibm.com>
> --- > arch/arm64/kernel/debug-monitors.c | 14 ++++++++------ > 1 file changed, 8 insertions(+), 6 deletions(-) > > diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c > index f8719bd30850..48222a4760c2 100644 > --- a/arch/arm64/kernel/debug-monitors.c > +++ b/arch/arm64/kernel/debug-monitors.c > @@ -207,16 +207,16 @@ static int call_step_hook(struct pt_regs *regs, unsigned int esr) > > list = user_mode(regs) ? &user_step_hook : &kernel_step_hook; > > - rcu_read_lock(); > - > + /* > + * Since single-step exception disables interrupt, this function is > + * entirely not preemptible, and we can use rcu list safely here. > + */ > list_for_each_entry_rcu(hook, list, node) { > retval = hook->fn(regs, esr); > if (retval == DBG_HOOK_HANDLED) > break; > } > > - rcu_read_unlock(); > - > return retval; > } > NOKPROBE_SYMBOL(call_step_hook); > @@ -305,14 +305,16 @@ static int call_break_hook(struct pt_regs *regs, unsigned int esr) > > list = user_mode(regs) ? &user_break_hook : &kernel_break_hook; > > - rcu_read_lock(); > + /* > + * Since brk exception disables interrupt, this function is > + * entirely not preemptible, and we can use rcu list safely here. > + */ > list_for_each_entry_rcu(hook, list, node) { > unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK; > > if ((comment & ~hook->mask) == hook->imm) > fn = hook->fn; > } > - rcu_read_unlock(); > > return fn ? fn(regs, esr) : DBG_HOOK_ERROR; > } >
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