On Mon, Nov 06, 2023 at 01:12:07PM +0100, Stefan Wiehler wrote:
> rcutree_report_cpu_starting() must be called before
> clockevents_register_device() to avoid the following lockdep splat triggered by
> calling list_add() when CONFIG_PROVE_RCU_LIST=y:
>
> WARNING: suspicious RCU usage
> ...
> -----------------------------
> kernel/locking/lockdep.c:3680 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.
> ...
> Call Trace:
> [<ffffffff8012a434>] show_stack+0x64/0x158
> [<ffffffff80a93d98>] dump_stack_lvl+0x90/0xc4
> [<ffffffff801c9e9c>] __lock_acquire+0x1404/0x2940
> [<ffffffff801cbf3c>] lock_acquire+0x14c/0x448
> [<ffffffff80aa4260>] _raw_spin_lock_irqsave+0x50/0x88
> [<ffffffff8021e0c8>] clockevents_register_device+0x60/0x1e8
> [<ffffffff80130ff0>] r4k_clockevent_init+0x220/0x3a0
> [<ffffffff801339d0>] start_secondary+0x50/0x3b8
>
> raw_smp_processor_id() is required in order to avoid calling into lockdep
> before RCU has declared the CPU to be watched for readers.
>
> See also commit 29368e093921 ("x86/smpboot: Move rcu_cpu_starting() earlier"),
> commit de5d9dae150c ("s390/smp: move rcu_cpu_starting() earlier") and commit
> 99f070b62322 ("powerpc/smp: Call rcu_cpu_starting() earlier").
>
> Signed-off-by: Stefan Wiehler <stefan.wiehler@xxxxxxxxx>
> ---
> - Rename rcu_cpu_starting() to rcutree_report_cpu_starting() due to commit
> 448e9f34d91d ("rcu: Standardize explicit CPU-hotplug calls")
> ---
> arch/mips/kernel/smp.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
applied to mips-fixes.
Thomas.
--
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea. [ RFC1925, 2.3 ]
