linux-kernel - Re: [PATCH V2 2/4] LoongArch: Fix sleeping in atomic context for PREEMPT

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Message-ID: <20241120074049.hw2lHvyM@linutronix.de>
Date: Wed, 20 Nov 2024 08:40:49 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Huacai Chen <chenhuacai@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>, loongarch@...ts.linux.dev,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	linux-rt-devel@...ts.linux.dev, Xuerui Wang <kernel@...0n.name>,
	Jiaxun Yang <jiaxun.yang@...goat.com>, linux-kernel@...r.kernel.org,
	loongson-kernel@...ts.loongnix.cn
Subject: Re: [PATCH V2 2/4] LoongArch: Fix sleeping in atomic context for
 PREEMPT_RT

On 2024-11-17 13:40:15 [+0800], Huacai Chen wrote:
> Commit bab1c299f3945ffe79 ("LoongArch: Fix sleeping in atomic context in
> setup_tlb_handler()") changes the gfp flag from GFP_KERNEL to GFP_ATOMIC
> for alloc_pages_node(). However, for PREEMPT_RT kernels we can still get
> a "sleeping in atomic context" error:
> 
> [    0.372259] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
> [    0.372266] in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/1
> [    0.372268] preempt_count: 1, expected: 0
> [    0.372270] RCU nest depth: 1, expected: 1
> [    0.372272] 3 locks held by swapper/1/0:
> [    0.372274]  #0: 900000000c9f5e60 (&pcp->lock){+.+.}-{3:3}, at: get_page_from_freelist+0x524/0x1c60
> [    0.372294]  #1: 90000000087013b8 (rcu_read_lock){....}-{1:3}, at: rt_spin_trylock+0x50/0x140
> [    0.372305]  #2: 900000047fffd388 (&zone->lock){+.+.}-{3:3}, at: __rmqueue_pcplist+0x30c/0xea0
> [    0.372314] irq event stamp: 0
> [    0.372316] hardirqs last  enabled at (0): [<0000000000000000>] 0x0
> [    0.372322] hardirqs last disabled at (0): [<9000000005947320>] copy_process+0x9c0/0x26e0
> [    0.372329] softirqs last  enabled at (0): [<9000000005947320>] copy_process+0x9c0/0x26e0
> [    0.372335] softirqs last disabled at (0): [<0000000000000000>] 0x0
> [    0.372341] CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted 6.12.0-rc7+ #1891
> [    0.372346] Hardware name: Loongson Loongson-3A5000-7A1000-1w-CRB/Loongson-LS3A5000-7A1000-1w-CRB, BIOS vUDK2018-LoongArch-V2.0.0-prebeta9 10/21/2022
> [    0.372349] Stack : 0000000000000089 9000000005a0db9c 90000000071519c8 9000000100388000
> [    0.372486]         900000010038b890 0000000000000000 900000010038b898 9000000007e53788
> [    0.372492]         900000000815bcc8 900000000815bcc0 900000010038b700 0000000000000001
> [    0.372498]         0000000000000001 4b031894b9d6b725 00000000055ec000 9000000100338fc0
> [    0.372503]         00000000000000c4 0000000000000001 000000000000002d 0000000000000003
> [    0.372509]         0000000000000030 0000000000000003 00000000055ec000 0000000000000003
> [    0.372515]         900000000806d000 9000000007e53788 00000000000000b0 0000000000000004
> [    0.372521]         0000000000000000 0000000000000000 900000000c9f5f10 0000000000000000
> [    0.372526]         90000000076f12d8 9000000007e53788 9000000005924778 0000000000000000
> [    0.372532]         00000000000000b0 0000000000000004 0000000000000000 0000000000070000
> [    0.372537]         ...
> [    0.372540] Call Trace:
> [    0.372542] [<9000000005924778>] show_stack+0x38/0x180
> [    0.372548] [<90000000071519c4>] dump_stack_lvl+0x94/0xe4
> [    0.372555] [<900000000599b880>] __might_resched+0x1a0/0x260
> [    0.372561] [<90000000071675cc>] rt_spin_lock+0x4c/0x140
> [    0.372565] [<9000000005cbb768>] __rmqueue_pcplist+0x308/0xea0
> [    0.372570] [<9000000005cbed84>] get_page_from_freelist+0x564/0x1c60
> [    0.372575] [<9000000005cc0d98>] __alloc_pages_noprof+0x218/0x1820
> [    0.372580] [<900000000593b36c>] tlb_init+0x1ac/0x298
> [    0.372585] [<9000000005924b74>] per_cpu_trap_init+0x114/0x140
> [    0.372589] [<9000000005921964>] cpu_probe+0x4e4/0xa60
> [    0.372592] [<9000000005934874>] start_secondary+0x34/0xc0
> [    0.372599] [<900000000715615c>] smpboot_entry+0x64/0x6c
> 
> This is because in PREEMPT_RT kernels normal spinlocks are replaced by
> rt spinlocks and rt_spin_lock() will cause sleeping. Fix it by disabling
> NUMA optimization completely for PREEMPT_RT kernels.
> 
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>  arch/loongarch/mm/tlb.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/loongarch/mm/tlb.c b/arch/loongarch/mm/tlb.c
> index 5ac9beb5f093..3b427b319db2 100644
> --- a/arch/loongarch/mm/tlb.c
> +++ b/arch/loongarch/mm/tlb.c
> @@ -289,7 +289,7 @@ static void setup_tlb_handler(int cpu)
>  		/* Avoid lockdep warning */
>  		rcutree_report_cpu_starting(cpu);
>  
> -#ifdef CONFIG_NUMA
> +#if defined(CONFIG_NUMA) && !defined(CONFIG_PREEMPT_RT)
>  		vec_sz = sizeof(exception_handlers);

How does this work with NUMA and RT? You don't allocate memory and
everything is fine? Couldn't you pre-allocate the memory on the boot CPU
before kicking the CPU to boot? And then just assign the memory here.

>  		if (pcpu_handlers[cpu])

Sebastian