[PATCH 5.4 2/9] x86/smpboot: Move rcu_cpu_starting() earlier

Greg Kroah-Hartman
2022-12-15T18:11:19Z

From: Paul E. McKenney <paulmck@kernel.org>

commit 29368e09392123800e5e2bf0f3eda91f16972e52 upstream.

The call to rcu_cpu_starting() in mtrr_ap_init() is not early enough
in the CPU-hotplug onlining process, which results in lockdep splats
as follows:

=============================
WARNING: suspicious RCU usage
5.9.0+ #268 Not tainted
-----------------------------
kernel/kprobes.c:300 RCU-list traversed in non-reader section!!

other info that might help us debug this:

RCU used illegally from offline CPU!
rcu_scheduler_active = 1, debug_locks = 1
no locks held by swapper/1/0.

stack backtrace:
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 5.9.0+ #268
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.10.2-1ubuntu1 04/01/2014
Call Trace:
dump_stack+0x77/0x97
__is_insn_slot_addr+0x15d/0x170
kernel_text_address+0xba/0xe0
? get_stack_info+0x22/0xa0
__kernel_text_address+0x9/0x30
show_trace_log_lvl+0x17d/0x380
? dump_stack+0x77/0x97
dump_stack+0x77/0x97
__lock_acquire+0xdf7/0x1bf0
lock_acquire+0x258/0x3d0
? vprintk_emit+0x6d/0x2c0
_raw_spin_lock+0x27/0x40
? vprintk_emit+0x6d/0x2c0
vprintk_emit+0x6d/0x2c0
printk+0x4d/0x69
start_secondary+0x1c/0x100
secondary_startup_64_no_verify+0xb8/0xbb

This is avoided by moving the call to rcu_cpu_starting up near
the beginning of the start_secondary() function. Note that the
raw_smp_processor_id() is required in order to avoid calling into lockdep
before RCU has declared the CPU to be watched for readers.

Link: https://lore.kernel.org/lkml/160223032121.7002.1269740091547117869.tip-bot2@tip-bot2/
Reported-by: Qian Cai <cai@redhat.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kernel/cpu/mtrr/mtrr.c | 2 --
arch/x86/kernel/smpboot.c | 1 +
2 files changed, 1 insertion(+), 2 deletions(-)

--- a/arch/x86/kernel/cpu/mtrr/mtrr.c
+++ b/arch/x86/kernel/cpu/mtrr/mtrr.c
@@ -794,8 +794,6 @@ void mtrr_ap_init(void)
if (!use_intel() || mtrr_aps_delayed_init)
return;

- rcu_cpu_starting(smp_processor_id());
-
/*
* Ideally we should hold mtrr_mutex here to avoid mtrr entries
* changed, but this routine will be called in cpu boot time,
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -224,6 +224,7 @@ static void notrace start_secondary(void
#endif
load_current_idt();
cpu_init();
+ rcu_cpu_starting(raw_smp_processor_id());
x86_cpuinit.early_percpu_clock_init();
preempt_disable();
smp_callin();