From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
X86 ML <x86@kernel.org>, "Paul E. McKenney" <paulmck@kernel.org>,
Alexandre Chartre <alexandre.chartre@oracle.com>,
Frederic Weisbecker <frederic@kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Sean Christopherson <sean.j.christopherson@intel.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Joel Fernandes <joel@joelfernandes.org>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Juergen Gross <jgross@suse.com>, Brian Gerst <brgerst@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Will Deacon <will@kernel.org>,
Tom Lendacky <thomas.lendacky@amd.com>,
Wei Liu <wei.liu@kernel.org>,
Michael Kelley <mikelley@microsoft.com>,
Jason Chen CJ <jason.cj.chen@intel.com>,
Zhao Yakui <yakui.zhao@intel.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>
Subject: Re: [patch V9 04/39] x86/entry: Provide idtentry_entry/exit_cond_rcu()
Date: Tue, 26 May 2020 10:23:03 +0200 [thread overview]
Message-ID: <20200526082303.GB35238@gmail.com> (raw)
In-Reply-To: <20200521202117.181397835@linutronix.de>
* Thomas Gleixner <tglx@linutronix.de> wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
>
> After a lengthy discussion [1] it turned out that RCU does not need a full
> rcu_irq_enter/exit() when RCU is already watching. All it needs if
> NOHZ_FULL is active is to check whether the tick needs to be restarted.
>
> This allows to avoid a separate variant for the pagefault handler which
> cannot invoke rcu_irq_enter() on a kernel pagefault which might sleep.
>
> The cond_rcu argument is only temporary and will be removed once the
> existing users of idtentry_enter/exit() have been cleaned up. After that
> the code can be significantly simplified.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Link: [1] https://lkml.kernel.org/r/20200515235125.628629605@linutronix.de
> ---
> V9: Reworked to the new RCU mode
> ---
> arch/x86/entry/common.c | 84 ++++++++++++++++++++++++++++++----------
> arch/x86/include/asm/idtentry.h | 14 +++++-
> 2 files changed, 77 insertions(+), 21 deletions(-)
>
> --- a/arch/x86/entry/common.c
> +++ b/arch/x86/entry/common.c
> @@ -512,8 +512,10 @@ SYSCALL_DEFINE0(ni_syscall)
> }
>
> /**
> - * idtentry_enter - Handle state tracking on idtentry
> + * idtentry_enter_cond_rcu - Handle state tracking on idtentry with conditional
> + * RCU handling
> * @regs: Pointer to pt_regs of interrupted context
> + * @cond_rcu: Invoke rcu_irq_enter() only if RCU is not watching
> *
> * Invokes:
> * - lockdep irqflag state tracking as low level ASM entry disabled
> @@ -521,40 +523,81 @@ SYSCALL_DEFINE0(ni_syscall)
> *
> * - Context tracking if the exception hit user mode.
> *
> - * - RCU notification if the exception hit kernel mode.
> - *
> * - The hardirq tracer to keep the state consistent as low level ASM
> * entry disabled interrupts.
> + *
> + * For kernel mode entries RCU handling is done conditional. If RCU is
> + * watching then the only RCU requirement is to check whether the tick has
> + * to be restarted. If RCU is not watching then rcu_irq_enter() has to be
> + * invoked on entry and rcu_irq_exit() on exit.
> + *
> + * Avoiding the rcu_irq_enter/exit() calls is an optimization but also
> + * solves the problem of kernel mode pagefaults which can schedule, which
> + * is not possible after invoking rcu_irq_enter() without undoing it.
> + *
> + * For user mode entries enter_from_user_mode() must be invoked to
> + * establish the proper context for NOHZ_FULL. Otherwise scheduling on exit
> + * would not be possible.
> + *
> + * Returns: True if RCU has been adjusted on a kernel entry
> + * False otherwise
> + *
> + * The return value must be fed into the rcu_exit argument of
> + * idtentry_exit_cond_rcu().
> */
> -void noinstr idtentry_enter(struct pt_regs *regs)
> +bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs, bool cond_rcu)
> {
> if (user_mode(regs)) {
> enter_from_user_mode();
> } else {
> - lockdep_hardirqs_off(CALLER_ADDR0);
> - rcu_irq_enter();
> - instrumentation_begin();
> - trace_hardirqs_off_prepare();
> - instrumentation_end();
> + if (!cond_rcu || !__rcu_is_watching()) {
> + /*
> + * If RCU is not watching then the same careful
> + * sequence vs. lockdep and tracing is required
> + * as in enter_from_user_mode().
> + *
> + * This only happens for IRQs that hits the idle
> + * loop, i.e. if idle is not using MWAIT.
> + */
> + lockdep_hardirqs_off(CALLER_ADDR0);
> + rcu_irq_enter();
> + instrumentation_begin();
> + trace_hardirqs_off_prepare();
> + instrumentation_end();
> + return true;
> + } else {
> + /*
> + * If RCU is watching then RCU only wants to check
> + * whether it needs to restart the tick in NOHZ
> + * mode.
> + */
> + instrumentation_begin();
> + rcu_irq_enter_check_tick();
> + /* Use the combo lockdep/tracing function */
> + trace_hardirqs_off();
> + instrumentation_end();
> + }
> }
> + return false;
> }
Any objections to the simplified/flattened control flow below?
Thanks,
Ingo
common.c | 59 +++++++++++++++++++++++++++++++----------------------------
1 file changed, 31 insertions(+), 28 deletions(-)
Index: tip/arch/x86/entry/common.c
===================================================================
--- tip.orig/arch/x86/entry/common.c
+++ tip/arch/x86/entry/common.c
@@ -549,35 +549,38 @@ bool noinstr idtentry_enter_cond_rcu(str
{
if (user_mode(regs)) {
enter_from_user_mode();
- } else {
- if (!cond_rcu || !__rcu_is_watching()) {
- /*
- * If RCU is not watching then the same careful
- * sequence vs. lockdep and tracing is required
- * as in enter_from_user_mode().
- *
- * This only happens for IRQs that hit the idle
- * loop, i.e. if idle is not using MWAIT.
- */
- lockdep_hardirqs_off(CALLER_ADDR0);
- rcu_irq_enter();
- instrumentation_begin();
- trace_hardirqs_off_prepare();
- instrumentation_end();
- return true;
- } else {
- /*
- * If RCU is watching then RCU only wants to check
- * whether it needs to restart the tick in NOHZ
- * mode.
- */
- instrumentation_begin();
- rcu_irq_enter_check_tick();
- /* Use the combo lockdep/tracing function */
- trace_hardirqs_off();
- instrumentation_end();
- }
+ return false;
}
+
+ if (!cond_rcu || !__rcu_is_watching()) {
+ /*
+ * If RCU is not watching then the same careful
+ * sequence vs. lockdep and tracing is required
+ * as in enter_from_user_mode().
+ *
+ * This only happens for IRQs that hit the idle
+ * loop, i.e. if idle is not using MWAIT.
+ */
+ lockdep_hardirqs_off(CALLER_ADDR0);
+ rcu_irq_enter();
+ instrumentation_begin();
+ trace_hardirqs_off_prepare();
+ instrumentation_end();
+
+ return true;
+ }
+
+ /*
+ * If RCU is watching then RCU only wants to check
+ * whether it needs to restart the tick in NOHZ
+ * mode.
+ */
+ instrumentation_begin();
+ rcu_irq_enter_check_tick();
+ /* Use the combo lockdep/tracing function */
+ trace_hardirqs_off();
+ instrumentation_end();
+
return false;
}
next prev parent reply other threads:[~2020-05-26 8:23 UTC|newest]
Thread overview: 132+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-21 20:05 [patch V9 00/39] x86/entry: Rework leftovers (was part V) Thomas Gleixner
2020-05-21 20:05 ` [patch V9 01/39] nmi, tracing: Make hardware latency tracing noinstr safe Thomas Gleixner
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 02/39] rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter() Thomas Gleixner
2020-05-21 21:03 ` Paul E. McKenney
2020-05-21 21:25 ` Thomas Gleixner
2020-05-26 8:14 ` Ingo Molnar
2020-05-26 15:34 ` Paul E. McKenney
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Paul E. McKenney
2020-05-21 20:05 ` [patch V9 03/39] rcu: Provide rcu_irq_exit_check_preempt() Thomas Gleixner
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 04/39] x86/entry: Provide idtentry_entry/exit_cond_rcu() Thomas Gleixner
2020-05-21 21:06 ` Paul E. McKenney
2020-05-26 8:23 ` Ingo Molnar [this message]
2020-05-26 8:58 ` Thomas Gleixner
2020-05-21 20:05 ` [patch V9 05/39] x86/entry: Provide idtentry_enter/exit_user() Thomas Gleixner
2020-05-27 8:12 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 06/39] x86/idtentry: Switch to conditional RCU handling Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 07/39] x86/entry: Cleanup idtentry_enter/exit() leftovers Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry: Clean up " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 08/39] genirq: Provide irq_enter/exit_rcu() Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 09/39] genirq: Provide __irq_enter/exit_raw() Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry: Provide helpers for executing on the irqstack tip-bot2 for Thomas Gleixner
2020-06-05 17:18 ` [patch V9 10/39] x86/entry: Provide helpers for execute on irqstack Qian Cai
2020-06-05 17:36 ` Peter Zijlstra
2020-06-05 17:52 ` Qian Cai
2020-06-07 11:59 ` Thomas Gleixner
2020-06-07 18:27 ` Qian Cai
2020-06-08 16:01 ` Qian Cai
2020-06-08 22:20 ` Thomas Gleixner
2020-06-09 2:32 ` Qian Cai
2020-06-09 20:33 ` Thomas Gleixner
2020-06-09 20:50 ` Thomas Gleixner
2020-06-10 12:38 ` Qian Cai
2020-06-10 19:38 ` Thomas Gleixner
2020-06-13 13:55 ` Qian Cai
2020-06-13 14:03 ` Thomas Gleixner
2020-06-13 21:41 ` Qian Cai
2020-06-14 8:59 ` Thomas Gleixner
2020-05-21 20:05 ` [patch V9 11/39] x86/entry/64: Move do_softirq_own_stack() to C Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 12/39] x86/entry: Split out idtentry_exit_cond_resched() Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 13/39] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY Thomas Gleixner
2020-05-22 18:32 ` [patch V9-1 " Thomas Gleixner
2020-05-26 7:44 ` Jürgen Groß
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 14/39] x86/entry/64: Simplify idtentry_body Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 15/39] x86/entry: Switch page fault exception to IDTENTRY_RAW Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 16/39] x86/entry: Remove the transition leftovers Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 17/39] x86/entry: Change exit path of xen_failsafe_callback Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 18/39] x86/entry/64: Remove error_exit Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry/64: Remove error_exit() tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 19/39] x86/entry/32: Remove common_exception Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/entry/32: Remove common_exception() tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 20/39] x86/irq: Use generic irq_regs implementation Thomas Gleixner
2020-05-26 18:39 ` damian
2020-05-28 9:50 ` Thomas Gleixner
2020-05-28 20:20 ` damian
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 21/39] x86/irq: Convey vector as argument and not in ptregs Thomas Gleixner
2020-05-22 19:34 ` Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-08-24 17:29 ` [patch V9 21/39] " Alexander Graf
2020-08-25 10:28 ` Thomas Gleixner
2020-08-25 23:17 ` Alexander Graf
2020-08-25 23:41 ` Andy Lutomirski
2020-08-26 0:04 ` Alexander Graf
2020-08-26 1:03 ` Brian Gerst
2020-08-26 0:55 ` Thomas Gleixner
2020-05-21 20:05 ` [patch V9 22/39] x86/irq: Rework handle_irq() for 64bit Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] x86/irq: Rework handle_irq() for 64-bit tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 23/39] x86/entry: Add IRQENTRY_IRQ macro Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 24/39] x86/entry: Use idtentry for interrupts Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 25/39] x86/entry: Provide IDTENTRY_SYSVEC Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 26/39] x86/entry: Convert APIC interrupts to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 27/39] x86/entry: Convert SMP system vectors " Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 28/39] x86/entry: Convert various system vectors Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 29/39] x86/entry: Convert KVM vectors to IDTENTRY_SYSVEC* Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 30/39] x86/entry: Convert various hypervisor vectors to IDTENTRY_SYSVEC Thomas Gleixner
2020-05-26 9:29 ` Wei Liu
2020-05-27 1:46 ` Boqun Feng
2020-05-27 8:38 ` Wei Liu
2020-05-27 12:09 ` Wei Liu
2020-05-27 23:06 ` Boqun Feng
2020-05-27 12:30 ` Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 31/39] x86/entry: Convert XEN hypercall vector " Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 32/39] x86/entry: Convert reschedule interrupt to IDTENTRY_SYSVEC_SIMPLE Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 33/39] x86/entry: Remove the apic/BUILD interrupt leftovers Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 34/39] x86/entry/64: Remove IRQ stack switching ASM Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 35/39] x86/entry: Make enter_from_user_mode() static Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 36/39] x86/entry/32: Remove redundant irq disable code Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 37/39] x86/entry/64: Remove TRACE_IRQS_*_DEBUG Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 38/39] x86/entry: Move paranoid irq tracing out of ASM code Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-21 20:05 ` [patch V9 39/39] x86/entry: Remove the TRACE_IRQS cruft Thomas Gleixner
2020-05-27 8:11 ` [tip: x86/entry] " tip-bot2 for Thomas Gleixner
2020-05-22 7:20 ` [patch V9 00/39] x86/entry: Rework leftovers (was part V) Andrew Cooper
2020-05-22 21:17 ` Peter Zijlstra
2020-06-03 19:18 ` Andrew Cooper
2020-06-04 13:25 ` Peter Zijlstra
2020-06-04 13:29 ` Paolo Bonzini
2020-06-04 13:35 ` Peter Zijlstra
2020-06-04 15:42 ` Andy Lutomirski
2020-06-04 15:55 ` Peter Zijlstra
2020-05-22 14:26 ` Boris Ostrovsky
2020-05-22 17:47 ` Thomas Gleixner
2020-05-22 18:08 ` Thomas Gleixner
2020-05-26 4:33 ` Andy Lutomirski
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