From: Guo Ren <guoren@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: arnd@arndb.de, palmer@rivosinc.com, tglx@linutronix.de,
luto@kernel.org, conor.dooley@microchip.com, heiko@sntech.de,
jszhang@kernel.org, lazyparser@gmail.com, falcon@tinylab.org,
chenhuacai@kernel.org, apatel@ventanamicro.com,
atishp@atishpatra.org, palmer@dabbelt.com,
paul.walmsley@sifive.com, mark.rutland@arm.com,
zouyipeng@huawei.com, bigeasy@linutronix.de,
David.Laight@aculab.com, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
Guo Ren <guoren@linux.alibaba.com>
Subject: Re: [PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning
Date: Tue, 20 Sep 2022 09:45:02 +0800 [thread overview]
Message-ID: <CAJF2gTQxfuHVe=drT3tMCK4prULR5iPS6F++HTokswjD2yRZZQ@mail.gmail.com> (raw)
In-Reply-To: <YyhZfUi17TEaOLWv@hirez.programming.kicks-ass.net>
On Mon, Sep 19, 2022 at 7:59 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Sun, Sep 18, 2022 at 11:52:41AM -0400, guoren@kernel.org wrote:
> > From: Guo Ren <guoren@linux.alibaba.com>
> >
> > 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@linux.alibaba.com>
> > Signed-off-by: Guo Ren <guoren@kernel.org>
> > ---
> > 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
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next prev parent reply other threads:[~2022-09-20 1:45 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-18 15:52 [PATCH V5 00/11] riscv: Add GENERIC_ENTRY support and related features guoren
2022-09-18 15:52 ` [PATCH V5 01/11] riscv: elf_kexec: Fixup compile warning guoren
2022-09-18 15:52 ` [PATCH V5 02/11] riscv: compat_syscall_table: " guoren
2022-09-18 15:52 ` [PATCH V5 03/11] riscv: ptrace: Remove duplicate operation guoren
2022-09-18 15:52 ` [PATCH V5 04/11] compiler_types.h: Add __noinstr_section() for noinstr guoren
2022-09-18 15:52 ` [PATCH V5 05/11] riscv: traps: Add noinstr to prevent instrumentation inserted guoren
2022-09-18 15:52 ` [PATCH V5 06/11] entry: Prevent DEBUG_PREEMPT warning guoren
2022-09-19 11:58 ` Peter Zijlstra
2022-09-20 1:45 ` Guo Ren [this message]
2022-09-30 12:27 ` Guo Ren
2022-09-18 15:52 ` [PATCH V5 07/11] riscv: convert to generic entry guoren
2022-09-19 13:34 ` Peter Zijlstra
2022-09-20 6:36 ` Guo Ren
2022-09-20 7:22 ` Peter Zijlstra
2022-09-30 11:28 ` Guo Ren
2022-09-18 15:52 ` [PATCH V5 08/11] riscv: Support HAVE_IRQ_EXIT_ON_IRQ_STACK guoren
2022-09-19 13:45 ` Peter Zijlstra
2022-09-20 6:08 ` Guo Ren
2022-09-20 7:27 ` Peter Zijlstra
2022-09-20 7:34 ` Peter Zijlstra
2022-09-21 6:16 ` Guo Ren
2022-09-21 8:34 ` Chen Zhongjin
2022-09-21 9:53 ` Guo Ren
2022-09-21 11:56 ` Chen Zhongjin
2022-09-22 1:26 ` Guo Ren
2022-09-18 15:52 ` [PATCH V5 09/11] riscv: Support HAVE_SOFTIRQ_ON_OWN_STACK guoren
2022-09-20 0:11 ` Guo Ren
2022-09-18 15:52 ` [PATCH V5 10/11] riscv: Add config of thread stack size guoren
2022-09-18 15:52 ` [PATCH V5 11/11] riscv: Add support for STACKLEAK gcc plugin guoren
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