On Mon, Sep 19, 2022 at 7:59 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Sun, Sep 18, 2022 at 11:52:41AM -0400, guoren@xxxxxxxxxx wrote: > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > > > When DEBUG_PREEMPT=y, > > exit_to_user_mode_prepare > > ->tick_nohz_user_enter_prepare > > ->tick_nohz_full_cpu(smp_processor_id()) > > ->smp_processor_id() > > ->debug_smp_processor_id() > > ->check preempt_count() then: > > > > [ 5.717610] BUG: using smp_processor_id() in preemptible [00000000] > > code: S20urandom/94 > > [ 5.718111] caller is debug_smp_processor_id+0x24/0x38 > > [ 5.718417] CPU: 1 PID: 94 Comm: S20urandom Not tainted > > 6.0.0-rc3-00010-gfd0a0d619c63-dirty #238 > > [ 5.718886] Hardware name: riscv-virtio,qemu (DT) > > [ 5.719136] Call Trace: > > [ 5.719281] [<ffffffff800055fc>] dump_backtrace+0x2c/0x3c > > [ 5.719566] [<ffffffff80ae6cb0>] show_stack+0x44/0x5c > > [ 5.720023] [<ffffffff80aee870>] dump_stack_lvl+0x74/0xa4 > > [ 5.720557] [<ffffffff80aee8bc>] dump_stack+0x1c/0x2c > > [ 5.721033] [<ffffffff80af65c0>] > > check_preemption_disabled+0x104/0x108 > > [ 5.721538] [<ffffffff80af65e8>] debug_smp_processor_id+0x24/0x38 > > [ 5.722001] [<ffffffff800aee30>] exit_to_user_mode_prepare+0x48/0x178 > > [ 5.722355] [<ffffffff80af5bf4>] irqentry_exit_to_user_mode+0x18/0x30 > > [ 5.722685] [<ffffffff80af5c70>] irqentry_exit+0x64/0xa4 > > [ 5.722953] [<ffffffff80af52f4>] do_page_fault+0x1d8/0x544 > > [ 5.723291] [<ffffffff80003310>] ret_from_exception+0x0/0xb8 > > > > (Above is found in riscv platform with generic_entry) > > > > The smp_processor_id() needs irqs disable or preempt_disable, so use > > preempt dis/in protecting the tick_nohz_user_enter_prepare(). > > > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx> > > --- > > kernel/entry/common.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/kernel/entry/common.c b/kernel/entry/common.c > > index 063068a9ea9b..36e4cd50531c 100644 > > --- a/kernel/entry/common.c > > +++ b/kernel/entry/common.c > > @@ -194,8 +194,10 @@ static void exit_to_user_mode_prepare(struct pt_regs *regs) > > > > lockdep_assert_irqs_disabled(); > > Observe ^^^^ Thanks! I would enable PROVE_LOCKING for test. > > > > > + preempt_disable(); > > /* Flush pending rcuog wakeup before the last need_resched() check */ > > tick_nohz_user_enter_prepare(); > > + preempt_enable(); > > This makes no sense; if IRQs are disabled, check_preemption_disabled() > should bail early per: > > if (irqs_disabled()) > goto out; Ditto. -- Best Regards Guo Ren
