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Message-ID: <5813b8c5-ae3e-87fd-fccc-94c9cd08816d@arm.com>
Date: Fri, 10 Feb 2023 17:42:52 +0000
From: James Morse <james.morse@....com>
To: Pierre Gondois <pierre.gondois@....com>,
linux-kernel@...r.kernel.org
Cc: Will Deacon <will@...nel.org>, Huacai Chen <chenhuacai@...nel.org>,
John Garry <john.garry@...wei.com>,
Shaokun Zhang <zhangshaokun@...ilicon.com>,
WANG Xuerui <git@...0n.name>, Qi Liu <liuqi115@...wei.com>,
Bharat Bhushan <bbhushan2@...vell.com>,
Huang Ying <ying.huang@...el.com>,
Bibo Mao <maobibo@...ngson.cn>,
"Jason A. Donenfeld" <Jason@...c4.com>,
Daniel Lezcano <daniel.lezcano@...aro.org>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] firmware: arm_sdei: Fix sleep from invalid context BUG
Hi Pierre,
Sorry its taken so long for me to catch up with this ...
On 18/10/2022 14:04, Pierre Gondois wrote:
> On an Ampere Altra,
> Running a preemp_rt kernel based on v5.19-rc3-rt5 on an
> Ampere Altra triggers:
> [ 15.683141] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
> [ 15.683154] in_atomic(): 0, irqs_disabled(): 128, non_block: 0, pid: 24, name: cpuhp/0
> [ 15.683157] preempt_count: 0, expected: 0
> [ 15.683159] RCU nest depth: 0, expected: 0
> [ 15.683163] 3 locks held by cpuhp/0/24:
> [ 15.683167] #0: ffffda30217c70d0 (cpu_hotplug_lock){++++}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
> [ 15.683201] #1: ffffda30217c7120 (cpuhp_state-up){+.+.}-{0:0}, at: cpuhp_thread_fun+0x5c/0x248
> [ 15.683205] #2: ffffda3021c711f0 (sdei_list_lock){....}-{3:3}, at: sdei_cpuhp_up+0x3c/0x130
> [ 15.683224] irq event stamp: 36
> [ 15.683226] hardirqs last enabled at (35): [<ffffda301e85b7bc>] finish_task_switch+0xb4/0x2b0
> [ 15.683236] hardirqs last disabled at (36): [<ffffda301e812fec>] cpuhp_thread_fun+0x21c/0x248
> [ 15.683238] softirqs last enabled at (0): [<ffffda301e80b184>] copy_process+0x63c/0x1ac0
> [ 15.683245] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [ 15.683258] CPU: 0 PID: 24 Comm: cpuhp/0 Not tainted 5.19.0-rc3-rt5-[...]
> [ 15.683265] Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18
> [ 15.683268] Call trace:
> [ 15.683271] dump_backtrace+0x114/0x120
> [ 15.683277] show_stack+0x20/0x70
> [ 15.683279] dump_stack_lvl+0x9c/0xd8
> [ 15.683288] dump_stack+0x18/0x34
> [ 15.683289] __might_resched+0x188/0x228
> [ 15.683292] rt_spin_lock+0x70/0x120
> [ 15.683301] sdei_cpuhp_up+0x3c/0x130
> [ 15.683303] cpuhp_invoke_callback+0x250/0xf08
> [ 15.683305] cpuhp_thread_fun+0x120/0x248
> [ 15.683308] smpboot_thread_fn+0x280/0x320
> [ 15.683315] kthread+0x130/0x140
> [ 15.683321] ret_from_fork+0x10/0x20
> sdei_cpuhp_up() is called in the STARTING hotplug section,
> which runs whith interrupts disabled. Move CPUHP_AP_ARM_SDEI_
> state to the _ONLINE section to execute the cpuhp cb with
> preemption enabled.
The background to this is SDEI got its own cpuhp slot because 'perf NMI' support
was one of the use-cases, but this got superseded by pNMI. Without an interaction with
perf, the slot doesn't need to be that early.
> Some SDEI calls (e.g. SDEI_1_0_FN_SDEI_PE_MASK) take actions on the
> calling CPU. It is checked that preemption is disabled for them.
> _ONLINE cpuhp cb are executed in the 'per CPU hotplug thread'.
> Preemption is enabled in those threads, but their cpumask is limited
> to 1 CPU.
> Move 'WARN_ON_ONCE(preemptible())' statements so that SDEI cpuhp cb
> don't trigger them. This means that no check will be done for some
> cases, e.g. sdei_mask_local_cpu() invocations.
(these things are documentation anyway)
> Also add a check for the SDEI_1_0_FN_SDEI_PRIVATE_RESET SDEI call
> which acts on the calling CPU.
> diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
> index 1e1a51510e83..9b03e164a37a 100644
> --- a/drivers/firmware/arm_sdei.c
> +++ b/drivers/firmware/arm_sdei.c
> @@ -401,6 +399,8 @@ int sdei_event_enable(u32 event_num)
> int err = -EINVAL;
> struct sdei_event *event;
>
> + WARN_ON_ONCE(preemptible());
> +
> mutex_lock(&sdei_events_lock);
> event = sdei_event_find(event_num);
> if (!event) {
This doesn't look right. How can this code take a mutex if its in a non-preemptable context?
> @@ -492,6 +490,7 @@ int sdei_event_unregister(u32 event_num)
> struct sdei_event *event;
>
> WARN_ON(in_nmi());
> + WARN_ON_ONCE(preemptible());
>
> mutex_lock(&sdei_events_lock);
> event = sdei_event_find(event_num);
Same again.
> @@ -576,6 +573,7 @@ int sdei_event_register(u32 event_num, sdei_event_callback *cb, void *arg)
> struct sdei_event *event;
>
> WARN_ON(in_nmi());
> + WARN_ON_ONCE(preemptible());
>
> mutex_lock(&sdei_events_lock);
> if (sdei_event_find(event_num)) {
Same again.
I think you've copied these here because they called _local_event_unregister(), but they
did that via on_each_cpu(), which is what made _local_event_unregister() non-preemtable.
You can just remove these three, the original warnings were mostly documentation, and to
catch myself out. (before RT moved the goal posts).
With that:
Reviewed-by: James Morse <james.morse@....com>
(could you trim the [timestamps] out of the commit log?)
> @@ -765,7 +765,7 @@ static int sdei_device_freeze(struct device *dev)
> int err;
>
> /* unregister private events */
> - cpuhp_remove_state(CPUHP_AP_ARM_SDEI_STARTING);
> + cpuhp_remove_state(CPUHP_AP_ARM_SDEI_ONLINE);
Is there any mileage in making this CPUHP_AP_ONLINE_DYN ?
Perf really was the only reason that this needed to happen in any particular order.
Thanks,
James
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