From: Masami Hiramatsu <mhiramat@kernel.org>
To: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>
Cc: Dan Rue <dan.rue@linaro.org>,
Daniel Diaz <daniel.diaz@linaro.org>,
Anders Roxell <anders.roxell@linaro.org>,
Naresh Kamboju <naresh.kamboju@linaro.org>,
linux-kernel@vger.kernel.org, Matt Hart <matthew.hart@linaro.org>,
"Paul E . McKenney" <paulmck@linux.ibm.com>,
linux-arm-kernel@lists.infradead.org, mhiramat@kernel.org
Subject: [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception
Date: Thu, 18 Jul 2019 14:43:58 +0900 [thread overview]
Message-ID: <156342863822.8565.7624877983728871995.stgit@devnote2> (raw)
In-Reply-To: <156342860634.8565.14804606041960884732.stgit@devnote2>
Remove rcu_read_lock()/rcu_read_unlock() from debug exception
handlers since the software breakpoint can be hit on idle task.
Actually, we don't need it because those handlers run in exception
context where the interrupts are disabled. This means those are never
preempted.
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
---
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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next prev parent reply other threads:[~2019-07-18 5:44 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-18 5:43 [PATCH 0/3] arm64: kprobes: Fix some bugs in arm64 kprobes Masami Hiramatsu
2019-07-18 5:43 ` [PATCH 1/3] arm64: kprobes: Recover pstate.D in single-step exception handler Masami Hiramatsu
2019-07-19 10:07 ` James Morse
2019-07-20 6:22 ` Masami Hiramatsu
2019-07-18 5:43 ` [PATCH 2/3] arm64: unwind: Prohibit probing on return_address() Masami Hiramatsu
2019-07-18 5:43 ` Masami Hiramatsu [this message]
2019-07-18 6:22 ` [PATCH 3/3] arm64: debug: Remove rcu_read_lock from debug exception Paul E. McKenney
2019-07-18 9:20 ` Mark Rutland
2019-07-18 14:31 ` Masami Hiramatsu
2019-07-19 8:42 ` James Morse
2019-07-20 7:32 ` Masami Hiramatsu
2019-07-21 1:50 ` Masami Hiramatsu
2019-07-19 9:59 ` Mark Rutland
2019-07-20 7:54 ` Masami Hiramatsu
2019-07-24 10:45 ` Mark Rutland
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