linux-kernel - Re: [PATCH v2] mm/memory-failure: Use raw_spinlock_t in struct memory_failure

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Message-ID: <1ea73082-f8f0-6c6d-3c0c-9012520d1036@huawei.com>
Date: Wed, 7 Aug 2024 11:15:16 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Waiman Long <longman@...hat.com>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, Huang Ying
	<ying.huang@...el.com>, Len Brown <len.brown@...el.com>, Juri Lelli
	<juri.lelli@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Naoya
 Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2] mm/memory-failure: Use raw_spinlock_t in struct
 memory_failure_cpu

On 2024/8/7 0:41, 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. Also move the
> pr_err() out of the lock critical section to avoid indeterminate latency
> of this call.
> 
> Fixes: ea8f5fb8a71f ("HWPoison: add memory_failure_queue()")

We shouldn't have this problem before RT spinlock is supported? If so, this Fixes tag might be wrong.

> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  mm/memory-failure.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 581d3e5c9117..7aeb5198c2a0 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2417,7 +2417,7 @@ struct memory_failure_entry {
>  struct memory_failure_cpu {
>  	DECLARE_KFIFO(fifo, struct memory_failure_entry,
>  		      MEMORY_FAILURE_FIFO_SIZE);
> -	spinlock_t lock;
> +	raw_spinlock_t lock;
>  	struct work_struct work;
>  };
>  
> @@ -2443,19 +2443,21 @@ void memory_failure_queue(unsigned long pfn, int flags)
>  {
>  	struct memory_failure_cpu *mf_cpu;
>  	unsigned long proc_flags;
> +	bool buffer_overflow;
>  	struct memory_failure_entry entry = {
>  		.pfn =		pfn,
>  		.flags =	flags,
>  	};
>  
>  	mf_cpu = &get_cpu_var(memory_failure_cpu);
> -	spin_lock_irqsave(&mf_cpu->lock, proc_flags);
> -	if (kfifo_put(&mf_cpu->fifo, entry))
> +	raw_spin_lock_irqsave(&mf_cpu->lock, proc_flags);
> +	buffer_overflow = !kfifo_put(&mf_cpu->fifo, entry);
> +	if (!buffer_overflow)
>  		schedule_work_on(smp_processor_id(), &mf_cpu->work);
> -	else
> +	raw_spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
> +	if (buffer_overflow)
>  		pr_err("buffer overflow when queuing memory failure at %#lx\n",
>  		       pfn);

Should we put pr_err() further under put_cpu_var()?

> -	spin_unlock_irqrestore(&mf_cpu->lock, proc_flags)
>  	put_cpu_var(memory_failure_cpu);
>  }

Will below diff be more straightforward?

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index b68953dc9fad..be172cbc6ca9 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -2553,20 +2553,23 @@ void memory_failure_queue(unsigned long pfn, int flags)
 {
        struct memory_failure_cpu *mf_cpu;
        unsigned long proc_flags;
+       bool buffer_overflow = false;
        struct memory_failure_entry entry = {
                .pfn =          pfn,
                .flags =        flags,
        };

        mf_cpu = &get_cpu_var(memory_failure_cpu);
-       spin_lock_irqsave(&mf_cpu->lock, proc_flags);
+       raw_spin_lock_irqsave(&mf_cpu->lock, proc_flags);
        if (kfifo_put(&mf_cpu->fifo, entry))
                schedule_work_on(smp_processor_id(), &mf_cpu->work);
        else
+               buffer_overflow = true;
+       raw_spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
+       put_cpu_var(memory_failure_cpu);
+       if (buffer_overflow)
                pr_err("buffer overflow when queuing memory failure at %#lx\n",
                       pfn);
-       spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
-       put_cpu_var(memory_failure_cpu);
 }
 EXPORT_SYMBOL_GPL(memory_failure_queue);

But no strong opinion.

Thanks.
.