linux-kernel - Re: [PATCH] mm/memory-failure: Use raw_spinlock_t in struct memory_failure

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Message-ID: <ZrJG6OtoQCUadS9L@jlelli-thinkpadt14gen4.remote.csb>
Date: Tue, 6 Aug 2024 17:53:12 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Waiman Long <longman@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Miaohe Lin <linmiaohe@...wei.com>,
	Naoya Horiguchi <nao.horiguchi@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Huang Ying <ying.huang@...el.com>,
	Len Brown <len.brown@...el.com>
Subject: Re: [PATCH] mm/memory-failure: Use raw_spinlock_t in struct
 memory_failure_cpu

Hi Waimain,

On 06/08/24 10:25, Waiman Long wrote:
> The memory_failure_cpu structure is a per-cpu structure. Access to its
> content requires the use of get_cpu_var() to lock in the current CPU
> and disable preemption. The use of a regular spinlock_t for locking
> purpose is fine for a non-RT kernel.
> 
> Since the integration of RT spinlock support into the v5.15 kernel,
> a spinlock_t in a RT kernel becomes a sleeping lock and taking a
> sleeping lock in a preemption disabled context is illegal resulting in
> the following kind of warning.
> 
>   [12135.732244] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
>   [12135.732248] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 270076, name: kworker/0:0
>   [12135.732252] preempt_count: 1, expected: 0
>   [12135.732255] RCU nest depth: 2, expected: 2
>     :
>   [12135.732420] Hardware name: Dell Inc. PowerEdge R640/0HG0J8, BIOS 2.10.2 02/24/2021
>   [12135.732423] Workqueue: kacpi_notify acpi_os_execute_deferred
>   [12135.732433] Call Trace:
>   [12135.732436]  <TASK>
>   [12135.732450]  dump_stack_lvl+0x57/0x81
>   [12135.732461]  __might_resched.cold+0xf4/0x12f
>   [12135.732479]  rt_spin_lock+0x4c/0x100
>   [12135.732491]  memory_failure_queue+0x40/0xe0
>   [12135.732503]  ghes_do_memory_failure+0x53/0x390
>   [12135.732516]  ghes_do_proc.constprop.0+0x229/0x3e0
>   [12135.732575]  ghes_proc+0xf9/0x1a0
>   [12135.732591]  ghes_notify_hed+0x6a/0x150
>   [12135.732602]  notifier_call_chain+0x43/0xb0
>   [12135.732626]  blocking_notifier_call_chain+0x43/0x60
>   [12135.732637]  acpi_ev_notify_dispatch+0x47/0x70
>   [12135.732648]  acpi_os_execute_deferred+0x13/0x20
>   [12135.732654]  process_one_work+0x41f/0x500
>   [12135.732695]  worker_thread+0x192/0x360
>   [12135.732715]  kthread+0x111/0x140
>   [12135.732733]  ret_from_fork+0x29/0x50
>   [12135.732779]  </TASK>
> 
> Fix it by using a raw_spinlock_t for locking instead.

IIUC this is executed to recover a fault condition already, so maybe
latencies are of no interest at that point, but I wonder if something
like 

https://elixir.bootlin.com/linux/v6.10.1/source/Documentation/locking/locktypes.rst#L434

would still work and save us from introducing a raw_spinlock?

Or maybe the critical section is anyway tiny and we don't care either?

Thanks,
Juri