From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: tglx@linutronix.de, mingo@kernel.org, will@kernel.org,
x86@kernel.org, linux-kernel@vger.kernel.org, elver@google.com,
paulmck@kernel.org, rjw@rjwysocki.net
Subject: Re: [RFC][PATCH 2/3] locking,entry: #PF vs TRACE_IRQFLAGS
Date: Fri, 7 Aug 2020 16:21:48 -0400 [thread overview]
Message-ID: <20200807162148.48d96247@oasis.local.home> (raw)
In-Reply-To: <20200807193018.060388629@infradead.org>
On Fri, 07 Aug 2020 21:23:38 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> Much of the complexity in irqenter_{enter,exit}() is due to #PF being
> the sole exception that can schedule from kernel context.
>
> One additional wrinkle with #PF is that it is non-maskable, it can
> happen _anywhere_. Due to this, and the wonders of tracing, we can get
> the 'normal' NMI nesting vs TRACE_IRQFLAGS:
>
> local_irq_disable()
> raw_local_irq_disable();
> trace_hardirqs_off();
>
> local_irq_enable();
Do you mean to have that ';' there? That is, it the below is called
from local_irq_enable(), right? A ';' means that local_irq_enable()
is completed.
> trace_hardirqs_on();
> <#PF>
> trace_hardirqs_off()
> ...
> if (!regs_irqs_disabled(regs)
regs has it disabled, so this is false, right?
> trace_hardirqs_on();
> </#PF>
I missed the '/' in the above. At first I thought this was another page
fault :-/
> // WHOOPS -- lockdep thinks IRQs are disabled again!
> raw_local_irqs_enable();
>
> Rework irqenter_{enter,exit}() to save/restore the software state.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> include/linux/entry-common.h | 1
> kernel/entry/common.c | 52 ++++++++++++++++++++-----------------------
> 2 files changed, 26 insertions(+), 27 deletions(-)
>
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -310,6 +310,7 @@ void irqentry_exit_to_user_mode(struct p
> #ifndef irqentry_state
> typedef struct irqentry_state {
> bool exit_rcu;
> + bool irqs_enabled;
Instead of passing a structure around, should we look at converting
"irqentry_state" into a flags field?
-- Steve
> } irqentry_state_t;
> #endif
>
next prev parent reply other threads:[~2020-08-07 20:21 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-07 19:23 [RFC][PATCH 0/3] Tracing, Idle, RCU and such goodness Peter Zijlstra
2020-08-07 19:23 ` [RFC][PATCH 1/3] sched,idle,rcu: Push rcu_idle deeper into the idle path Peter Zijlstra
2020-08-07 19:23 ` [RFC][PATCH 2/3] locking,entry: #PF vs TRACE_IRQFLAGS Peter Zijlstra
2020-08-07 20:21 ` Steven Rostedt [this message]
2020-08-10 11:57 ` peterz
2020-08-10 12:05 ` David Laight
2020-08-10 13:49 ` peterz
2020-08-07 19:23 ` [RFC][PATCH 3/3] lockdep,trace: Expose tracepoints Peter Zijlstra
2020-08-07 20:34 ` Steven Rostedt
2020-08-10 12:26 ` [RFC][PATCH v1.1 " peterz
2020-08-10 9:55 ` [RFC][PATCH 0/3] Tracing, Idle, RCU and such goodness Marco Elver
2020-08-10 12:11 ` peterz
2020-08-11 16:08 ` Paul E. McKenney
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