From: peterz@infradead.org
To: Guenter Roeck <linux@roeck-us.net>
Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, will@kernel.org,
npiggin@gmail.com, elver@google.com, jgross@suse.com,
paulmck@kernel.org, rostedt@goodmis.org, rjw@rjwysocki.net,
joel@joelfernandes.org, svens@linux.ibm.com, tglx@linutronix.de
Subject: Re: [PATCH v2 11/11] lockdep,trace: Expose tracepoints
Date: Wed, 2 Sep 2020 09:24:32 +0200 [thread overview]
Message-ID: <20200902072432.GI2674@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200902035146.GA45826@roeck-us.net>
On Tue, Sep 01, 2020 at 08:51:46PM -0700, Guenter Roeck wrote:
> On Fri, Aug 21, 2020 at 10:47:49AM +0200, Peter Zijlstra wrote:
> > The lockdep tracepoints are under the lockdep recursion counter, this
> > has a bunch of nasty side effects:
> >
> > - TRACE_IRQFLAGS doesn't work across the entire tracepoint
> >
> > - RCU-lockdep doesn't see the tracepoints either, hiding numerous
> > "suspicious RCU usage" warnings.
> >
> > Pull the trace_lock_*() tracepoints completely out from under the
> > lockdep recursion handling and completely rely on the trace level
> > recusion handling -- also, tracing *SHOULD* not be taking locks in any
> > case.
> >
>
> Wonder what is worse - the problem or its fix. This patch results in
> a number of WARNING backtraces for several archtectures/platforms.
> Reverting it fixes the problems.
Without all this there was a recursion that could crash. But yes,
tedious.
OTOH the warnings are about real bugs that were pre-existing, we now see
them and can fix them.
I'll reply to ARM separately, but let's have a peek at s390.
> s390:
>
> [ 19.490586] =============================
> [ 19.490752] WARNING: suspicious RCU usage
> [ 19.490921] 5.9.0-rc3 #1 Not tainted
> [ 19.491086] -----------------------------
> [ 19.491253] include/trace/events/lock.h:37 suspicious rcu_dereference_check() usage!
> [ 19.493147] [<00000000001d5de2>] lock_acquire+0x41a/0x498
> [ 19.493320] [<0000000000103b72>] enabled_wait+0xca/0x198
> [ 19.493493] [<0000000000103f80>] arch_cpu_idle+0x20/0x38
Does this help?
---
diff --git a/arch/s390/kernel/idle.c b/arch/s390/kernel/idle.c
index c73f50649e7e..f7f1e64e0d98 100644
--- a/arch/s390/kernel/idle.c
+++ b/arch/s390/kernel/idle.c
@@ -39,14 +39,13 @@ void enabled_wait(void)
local_irq_restore(flags);
/* Account time spent with enabled wait psw loaded as idle time. */
- /* XXX seqcount has tracepoints that require RCU */
- write_seqcount_begin(&idle->seqcount);
+ raw_write_seqcount_begin(&idle->seqcount);
idle_time = idle->clock_idle_exit - idle->clock_idle_enter;
idle->clock_idle_enter = idle->clock_idle_exit = 0ULL;
idle->idle_time += idle_time;
idle->idle_count++;
account_idle_time(cputime_to_nsecs(idle_time));
- write_seqcount_end(&idle->seqcount);
+ raw_write_seqcount_end(&idle->seqcount);
}
NOKPROBE_SYMBOL(enabled_wait);
next prev parent reply other threads:[~2020-09-02 7:25 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-21 8:47 [PATCH v2 00/11] TRACE_IRQFLAGS wreckage Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 01/11] lockdep: Use raw_cpu_*() for per-cpu variables Peter Zijlstra
2020-08-27 1:05 ` Joel Fernandes
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 02/11] cpuidle: Fixup IRQ state Peter Zijlstra
2020-08-21 17:36 ` Rafael J. Wysocki
2020-08-27 1:06 ` Joel Fernandes
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 03/11] sched,idle,rcu: Push rcu_idle deeper into the idle path Peter Zijlstra
2020-08-27 1:18 ` Joel Fernandes
2020-08-27 1:24 ` Joel Fernandes
2020-08-27 7:47 ` peterz
2020-08-27 7:53 ` Thomas Gleixner
2020-08-27 22:30 ` Joel Fernandes
2020-09-02 7:08 ` peterz
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 04/11] cpuidle: Make CPUIDLE_FLAG_TLB_FLUSHED generic Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 05/11] cpuidle: Move trace_cpu_idle() into generic code Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 06/11] x86/entry: Remove unused THUNKs Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 07/11] locking/lockdep: Cleanup Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 08/11] nds32: Implement arch_irqs_disabled() Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 09/11] arm64: " Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-08-21 8:47 ` [PATCH v2 10/11] lockdep: Only trace IRQ edges Peter Zijlstra
2020-08-26 0:47 ` Thomas Gleixner
2020-09-02 4:21 ` Guenter Roeck
2020-09-02 9:09 ` peterz
2020-09-02 9:12 ` peterz
2020-09-02 13:48 ` Guenter Roeck
2020-09-08 14:22 ` peterz
2020-09-08 14:40 ` Guenter Roeck
2020-09-08 15:41 ` [PATCH] sparc64: Fix irqtrace warnings on Ultra-S peterz
2020-08-21 8:47 ` [PATCH v2 11/11] lockdep,trace: Expose tracepoints Peter Zijlstra
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2020-09-02 3:51 ` [PATCH v2 11/11] " Guenter Roeck
2020-09-02 7:24 ` peterz [this message]
2020-09-02 13:21 ` Guenter Roeck
2020-09-02 8:56 ` peterz
2020-09-02 13:57 ` Guenter Roeck
2020-09-03 14:00 ` peterz
2020-09-03 14:13 ` peterz
2020-09-03 15:19 ` Guenter Roeck
2020-09-03 15:36 ` peterz
2020-09-03 15:54 ` Paul E. McKenney
2020-09-03 18:11 ` Guenter Roeck
2020-08-21 12:58 ` [PATCH v2 00/11] TRACE_IRQFLAGS wreckage peterz
2020-08-26 10:16 ` [PATCH v2 12/11] mips: Implement arch_irqs_disabled() peterz
2020-08-27 7:54 ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
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