There are a few tracepoints in the interrupt code path, which is before
irq_enter(), or after irq_exit(), like
trace_irq_entry()/trace_irq_exit() in do_IRQ(),
trace_timer_interrupt_entry()/trace_timer_interrupt_exit() in
timer_interrupt().
If the interrupt is from idle(), and because tracepoint contains RCU
read-side critical section, we could see following suspicious RCU usage
reported:
[ 145.127743] ===============================
[ 145.127747] [ INFO: suspicious RCU usage. ]
[ 145.127752] 3.6.0-rc3+ #1 Not tainted
[ 145.127755] -------------------------------
[ 145.127759] /root/.workdir/linux/arch/powerpc/include/asm/trace.h:33
suspicious rcu_dereference_check() usage!
[ 145.127765]
[ 145.127765] other info that might help us debug this:
[ 145.127765]
[ 145.127771]
[ 145.127771] RCU used illegally from idle CPU!
[ 145.127771] rcu_scheduler_active = 1, debug_locks = 0
[ 145.127777] RCU used illegally from extended quiescent state!
[ 145.127781] no locks held by swapper/0/0.
[ 145.127785]
[ 145.127785] stack backtrace:
[ 145.127789] Call Trace:
[ 145.127796] [c00000000108b530] [c000000000013c40] .show_stack
+0x70/0x1c0 (unreliable)
[ 145.127806] [c00000000108b5e0]
[c0000000000f59d8] .lockdep_rcu_suspicious+0x118/0x150
[ 145.127813] [c00000000108b680] [c00000000000fc58] .do_IRQ+0x498/0x500
[ 145.127820] [c00000000108b750] [c000000000003950]
hardware_interrupt_common+0x150/0x180
[ 145.127828] --- Exception: 501 at .plpar_hcall_norets+0x84/0xd4
[ 145.127828] LR = .check_and_cede_processor+0x38/0x70
[ 145.127836] [c00000000108bab0] [c0000000000665dc] .shared_cede_loop
+0x5c/0x100
[ 145.127844] [c00000000108bb70] [c000000000588ab0] .cpuidle_enter
+0x30/0x50
[ 145.127850] [c00000000108bbe0]
[c000000000588b0c] .cpuidle_enter_state+0x3c/0xb0
[ 145.127857] [c00000000108bc60] [c000000000589730] .cpuidle_idle_call
+0x150/0x6c0
[ 145.127863] [c00000000108bd30] [c000000000058440] .pSeries_idle
+0x10/0x40
[ 145.127870] [c00000000108bda0] [c00000000001683c] .cpu_idle
+0x18c/0x2d0
[ 145.127876] [c00000000108be60] [c00000000000b434] .rest_init
+0x124/0x1b0
[ 145.127884] [c00000000108bef0] [c0000000009d0d28] .start_kernel
+0x568/0x588
[ 145.127890] [c00000000108bf90] [c000000000009660] .start_here_common
+0x20/0x40
This is because the RCU usage in interrupt context should be used in
area marked by rcu_irq_enter()/rcu_irq_exit(), called in
irq_enter()/irq_exit() respectively.
Could we add a new tracepoint trace_***_rcuirq, like trace_***_rcuidle
to avoid the report? like the code attached below.
Or could we just move these tracepoints inside the
irq_enter()/irq_exit() area? (Seems not good for the timer_interrupt
case).
Thanks, Zhong
Signed-off-by: Li Zhong <zh...@linux.vnet.ibm.com>
---
arch/powerpc/kernel/irq.c | 4 ++--
arch/powerpc/kernel/time.c | 4 ++--
include/linux/tracepoint.h | 10 ++++++++++
3 files changed, 14 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index 1f017bb..f0ac4e7 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -489,7 +489,7 @@ void do_IRQ(struct pt_regs *regs)
struct pt_regs *old_regs = set_irq_regs(regs);
unsigned int irq;
- trace_irq_entry(regs);
+ trace_irq_entry_rcuirq(regs);
irq_enter();
@@ -514,7 +514,7 @@ void do_IRQ(struct pt_regs *regs)
irq_exit();
set_irq_regs(old_regs);
- trace_irq_exit(regs);
+ trace_irq_exit_rcuirq(regs);
}
void __init init_IRQ(void)
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index e49e931..cbd6607 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -493,7 +493,7 @@ void timer_interrupt(struct pt_regs * regs)
*/
may_hard_irq_enable();
- trace_timer_interrupt_entry(regs);
+ trace_timer_interrupt_entry_rcuirq(regs);
__get_cpu_var(irq_stat).timer_irqs++;
@@ -532,7 +532,7 @@ void timer_interrupt(struct pt_regs * regs)
irq_exit();
set_irq_regs(old_regs);
- trace_timer_interrupt_exit(regs);
+ trace_timer_interrupt_exit_rcuirq(regs);
}
/*
diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 802de56..f7672d5 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -161,6 +161,16 @@ static inline void tracepoint_synchronize_unregister(void)
rcu_idle_exit(), \
rcu_idle_enter()); \
} \
+ static inline void trace_##name##_rcuirq(proto) \
+ { \
+ if (static_key_false(&__tracepoint_##name.key)) \
+ __DO_TRACE(&__tracepoint_##name, \
+ TP_PROTO(data_proto), \
+ TP_ARGS(data_args), \
+ TP_CONDITION(cond), \
+ rcu_irq_enter(), \
+ rcu_irq_exit()); \
+ } \
static inline int \
register_trace_##name(void (*probe)(data_proto), void *data) \
{ \
--
1.7.1
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