linux-kernel - Re: [PATCH v2] memcg: Remove the lockdep assert from __mod_objcg

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Date: Tue, 28 May 2024 17:08:56 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: "Vlastimil Babka (SUSE)" <vbabka@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] memcg: Remove the lockdep assert from
 __mod_objcg_mlstate().

On 2024-05-28 07:59:57 [-0700], Shakeel Butt wrote:
> One question on VM_WARN_ON_IRQS_ENABLED() in __mod_memcg_lruvec_state().
> On a PREEMPT_RT kernel with CONFIG_DEBUG_VM, will that
> VM_WARN_ON_IRQS_ENABLED() cause a splat or VM_WARN_ON_IRQS_ENABLED is
> special on PREEMPT_RT kernels?

we have the following in the header file:

| #ifdef CONFIG_DEBUG_VM_IRQSOFF
| #define VM_WARN_ON_IRQS_ENABLED() WARN_ON_ONCE(!irqs_disabled())
| #else
| #define VM_WARN_ON_IRQS_ENABLED() do { } while (0)
| #endif

and this in Kconfig:
| config DEBUG_VM_IRQSOFF
|         def_bool DEBUG_VM && !PREEMPT_RT
|

which means on PREEMPT_RT we end up with "do {…"

Sebastian