From: "Paul E. McKenney" <paulmck@linux.ibm.com> To: Masami Hiramatsu <mhiramat@kernel.org> Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Naresh Kamboju <naresh.kamboju@linaro.org>, Dan Rue <dan.rue@linaro.org>, Matt Hart <matthew.hart@linaro.org>, Anders Roxell <anders.roxell@linaro.org>, Daniel Diaz <daniel.diaz@linaro.org> Subject: Re: [PATCH v2 4/4] arm64: Remove unneeded rcu_read_lock from debug handlers Date: Mon, 22 Jul 2019 05:07:58 -0700 [thread overview] Message-ID: <20190722120758.GB14271@linux.ibm.com> (raw) In-Reply-To: <156378175027.12011.5591853683946780785.stgit@devnote2> 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; > } >
WARNING: multiple messages have this Message-ID (diff)
From: "Paul E. McKenney" <paulmck@linux.ibm.com> To: Masami Hiramatsu <mhiramat@kernel.org> Cc: Dan Rue <dan.rue@linaro.org>, Daniel Diaz <daniel.diaz@linaro.org>, Anders Roxell <anders.roxell@linaro.org>, Catalin Marinas <catalin.marinas@arm.com>, Naresh Kamboju <naresh.kamboju@linaro.org>, Will Deacon <will.deacon@arm.com>, linux-kernel@vger.kernel.org, Matt Hart <matthew.hart@linaro.org>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 4/4] arm64: Remove unneeded rcu_read_lock from debug handlers Date: Mon, 22 Jul 2019 05:07:58 -0700 [thread overview] Message-ID: <20190722120758.GB14271@linux.ibm.com> (raw) In-Reply-To: <156378175027.12011.5591853683946780785.stgit@devnote2> 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; > } > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-07-22 12:08 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-07-22 7:48 [PATCH v2 0/4] arm64: kprobes: Fix some bugs in arm64 kprobes Masami Hiramatsu 2019-07-22 7:48 ` Masami Hiramatsu 2019-07-22 7:48 ` [PATCH v2 1/4] arm64: kprobes: Recover pstate.D in single-step exception handler Masami Hiramatsu 2019-07-22 7:48 ` Masami Hiramatsu 2019-07-23 16:03 ` James Morse 2019-07-23 16:03 ` James Morse 2019-07-24 13:09 ` Masami Hiramatsu 2019-07-24 13:09 ` Masami Hiramatsu 2019-07-22 7:48 ` [PATCH v2 2/4] arm64: unwind: Prohibit probing on return_address() Masami Hiramatsu 2019-07-22 7:48 ` Masami Hiramatsu 2019-07-23 16:04 ` James Morse 2019-07-23 16:04 ` James Morse 2019-07-24 7:39 ` Masami Hiramatsu 2019-07-24 7:39 ` Masami Hiramatsu 2019-07-22 7:48 ` [PATCH v2 3/4] arm64: Make debug exception handlers visible from RCU Masami Hiramatsu 2019-07-22 7:48 ` Masami Hiramatsu 2019-07-22 12:07 ` Paul E. McKenney 2019-07-22 12:07 ` Paul E. McKenney 2019-07-23 17:07 ` James Morse 2019-07-23 17:07 ` James Morse 2019-07-24 11:47 ` Masami Hiramatsu 2019-07-24 11:47 ` Masami Hiramatsu 2019-07-22 7:49 ` [PATCH v2 4/4] arm64: Remove unneeded rcu_read_lock from debug handlers Masami Hiramatsu 2019-07-22 7:49 ` Masami Hiramatsu 2019-07-22 12:07 ` Paul E. McKenney [this message] 2019-07-22 12:07 ` Paul E. McKenney
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