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Subject[PATCH] tracing: Add back in rcu_irq_enter/exit_irqson() for rcuidle tracepoints
On Wed, 5 Sep 2018 05:59:41 -0700
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com> wrote:

> On Wed, Sep 05, 2018 at 10:22:54AM +0200, Borislav Petkov wrote:
> > On Tue, Sep 04, 2018 at 01:53:21PM -0700, Paul E. McKenney wrote:
> > > I must defer to Borislav on this one. Assuming it has the desired
> > > effect, I am good with it.
> >
> > It did survive a bunch of reboots (the WARN would fire after boot
> > finishes, normally) so I guess we can run with it and see how it works
> > out in the next couple of weeks.
> >
> > Thanks guys!
>
> Woo-hoo!!! Thank you for testing this!
>

Here's the official patch if you want to add an Ack/review/tested-by:

-- Steve

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

Borislav reported the following splat:

=============================
WARNING: suspicious RCU usage
4.19.0-rc1+ #1 Not tainted
-----------------------------
./include/linux/rcupdate.h:631 rcu_read_lock() used illegally while idle!
other info that might help us debug this:

RCU used illegally from idle CPU!
rcu_scheduler_active = 2, debug_locks = 1
RCU used illegally from extended quiescent state!
1 lock held by swapper/0/0:
#0: 000000004557ee0e (rcu_read_lock){....}, at: perf_event_output_forward+0x0/0x130

stack backtrace:
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.19.0-rc1+ #1
Hardware name: LENOVO 2320CTO/2320CTO, BIOS G2ET86WW (2.06 ) 11/13/2012
Call Trace:
dump_stack+0x85/0xcb
perf_event_output_forward+0xf6/0x130
__perf_event_overflow+0x52/0xe0
perf_swevent_overflow+0x91/0xb0
perf_tp_event+0x11a/0x350
? find_held_lock+0x2d/0x90
? __lock_acquire+0x2ce/0x1350
? __lock_acquire+0x2ce/0x1350
? retint_kernel+0x2d/0x2d
? find_held_lock+0x2d/0x90
? tick_nohz_get_sleep_length+0x83/0xb0
? perf_trace_cpu+0xbb/0xd0
? perf_trace_buf_alloc+0x5a/0xa0
perf_trace_cpu+0xbb/0xd0
cpuidle_enter_state+0x185/0x340
do_idle+0x1eb/0x260
cpu_startup_entry+0x5f/0x70
start_kernel+0x49b/0x4a6
secondary_startup_64+0xa4/0xb0

This is due to the tracepoints moving to SRCU usage which does not require
RCU to be "watching". But perf uses these tracepoints with RCU and expects
it to be. Hence, we still need to add in the rcu_irq_enter/exit_irqson()
calls for "rcuidle" tracepoints. This is a temporary fix until we have SRCU
working in NMI context, and then perf can be converted to use that instead
of normal RCU.

Link: http://lkml.kernel.org/r/20180904162611.6a120068@gandalf.local.home

Cc: x86-ml <x86@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Reported-by: Borislav Petkov <bp@alien8.de>
Fixes: e6753f23d961d ("tracepoint: Make rcuidle tracepoint callers use SRCU")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
include/linux/tracepoint.h | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
index 7f2e16e76ac4..041f7e56a289 100644
--- a/include/linux/tracepoint.h
+++ b/include/linux/tracepoint.h
@@ -158,8 +158,10 @@ extern void syscall_unregfunc(void);
* For rcuidle callers, use srcu since sched-rcu \
* doesn't work from the idle path. \
*/ \
- if (rcuidle) \
+ if (rcuidle) { \
idx = srcu_read_lock_notrace(&tracepoint_srcu); \
+ rcu_irq_enter_irqson(); \
+ } \
\
it_func_ptr = rcu_dereference_raw((tp)->funcs); \
\
@@ -171,8 +173,10 @@ extern void syscall_unregfunc(void);
} while ((++it_func_ptr)->func); \
} \
\
- if (rcuidle) \
+ if (rcuidle) { \
+ rcu_irq_exit_irqson(); \
srcu_read_unlock_notrace(&tracepoint_srcu, idx);\
+ } \
\
preempt_enable_notrace(); \
} while (0)
--
2.13.6
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