From: Joel Fernandes <joelaf@google.com>
To: linux-kernel@vger.kernel.org
Cc: Joel Fernandes <joelaf@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
Peter Zilstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Tom Zanussi <tom.zanussi@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>
Subject: [PATCH v1 2/2] tracepoint: Prevent false-positive lockdep warnings
Date: Tue, 13 Mar 2018 14:43:27 -0700 [thread overview]
Message-ID: <20180313214327.37475-3-joelaf@google.com> (raw)
In-Reply-To: <20180313214327.37475-1-joelaf@google.com>
Since the last patch, lockdep hooks for irqs on/off will use the
tracepoint infrastructure. This can however cause false lockdep
warnings triggered by RCU code that does lockdep asserts.
There are 2 cases:
1) trace_hardirqs_off calls the lockdep_hardirqs_off hook, however
this call happens only after rcu_irq_enter_irqsoff. Due to this,
the lockdep assert that happens in the RCU path will think that
IRQs are kept on and will print a warning.
[ 0.001000] ------------[ cut here ]------------
[ 0.001000] IRQs not disabled as expected
[ 0.001000] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:1039
rcu_irq_enter+0x56/0x5d
[ 0.001000] Call Trace:
[ 0.001000] rcu_irq_enter_irqson+0x21/0x47
[ 0.001000] trace_hardirqs_off+0x53/0xcc
[ 0.001000] __down_trylock_console_sem+0x27/0x9d
[ 0.001000] console_trylock+0x10/0x50
[ 0.001000] vprintk_emit+0x2a8/0x400
[ 0.001000] printk+0x43/0x4b
[ 0.001000] lockdep_init+0x38/0xe3
[ 0.001000] start_kernel+0x326/0x446
[ 0.001000] secondary_startup_64+0xa5/0xb0
2) trace_hardirqs_on calls the lockdep_hardirqs_on hook, however
interrupts are enabled only after trace_hardirqs_on. In the meanwhile
lockdep falsely sets its state to hardirqs are enabled. For this reason,
rcu_irq_enter_irqson prints the following false warning claiming IRQs
are not disabled:
[ 0.001000] ------------[ cut here ]------------
[ 0.001000] IRQs not disabled as expected
[ 0.001000] WARNING: CPU: 0 PID: 0 at kernel/rcu/tree.c:886
rcu_irq_exit+0x56/0x5d
[ 0.001000] Call Trace:
[ 0.001000] rcu_irq_exit_irqson+0x21/0x47
[ 0.001000] trace_hardirqs_on+0xb9/0xd7
[ 0.001000] vprintk_emit+0x287/0x400
[ 0.001000] printk+0x43/0x4b
[ 0.001000] lockdep_init+0x38/0xe3
[ 0.001000] start_kernel+0x326/0x446
[ 0.001000] secondary_startup_64+0xa5/0xb0
To fix it, just disable lockdep checks before and enable it after
rcu_irq_exit_irqson.
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zilstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Joel Fernandes <joelaf@google.com>
---
include/linux/tracepoint.h | 23 +++++++++++++++++++++--
1 file changed, 21 insertions(+), 2 deletions(-)
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index c94f466d57ef..81eac3562787 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -137,8 +137,17 @@ extern void syscall_unregfunc(void);
\
if (!(cond)) \
return; \
- if (rcucheck) \
+ \
+ /* \
+ * lockdep hook for irqsoff may run only after \
+ * rcu_irq_enter_irqson so in the meanwhile don't do \
+ * lockdep checks to prevent false lockdep warnings \
+ */ \
+ if (rcucheck) { \
+ lockdep_off(); \
rcu_irq_enter_irqson(); \
+ lockdep_on(); \
+ } \
rcu_read_lock_sched_notrace(); \
it_func_ptr = rcu_dereference_sched((tp)->funcs); \
if (it_func_ptr) { \
@@ -149,8 +158,18 @@ extern void syscall_unregfunc(void);
} while ((++it_func_ptr)->func); \
} \
rcu_read_unlock_sched_notrace(); \
- if (rcucheck) \
+ \
+ /* \
+ * Turn off lockdep before calling rcu_irq_exit_irqson \
+ * since the lockdep irqson hook may have just run \
+ * but irqs are only after trace_hardirqs_off returns. \
+ * This can cause false lockdep warnings. \
+ */ \
+ if (rcucheck) { \
+ lockdep_off(); \
rcu_irq_exit_irqson(); \
+ lockdep_on(); \
+ } \
} while (0)
#ifndef MODULE
--
2.16.2.660.g709887971b-goog
prev parent reply other threads:[~2018-03-13 21:44 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-13 21:43 [PATCH v1 0/2] Improve preemptirq tracepoint usage Joel Fernandes
2018-03-13 21:43 ` [PATCH v1 1/2] tracing: Improve design of preemptirq tracepoints and its users Joel Fernandes
2018-03-15 19:51 ` kbuild test robot
2018-03-15 20:19 ` Joel Fernandes
2018-03-16 3:13 ` kbuild test robot
2018-03-16 3:28 ` Joel Fernandes
2018-03-16 8:22 ` [tracing] b648360016: WARNING:at_kernel/locking/lockdep.c:#check_flags kernel test robot
2018-03-13 21:43 ` Joel Fernandes [this message]
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