arm64: Remove unneeded rcu_read_lock from debug handlers

Remove rcu_read_lock()/rcu_read_unlock() from debug exception
handlers since we are sure those are not preemptible and
interrupts are off.

Acked-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/kernel/debug-monitors.c b/arch/arm64/kernel/debug-monitors.c
index f8719bd..48222a4 100644 (file)
--- 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;
 }