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Message-Id: <20221117123324.c3cdad45b3204d57b5f7bc3d@linux-foundation.org>
Date: Thu, 17 Nov 2022 12:33:24 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Zqiang <qiang1.zhang@...el.com>
Cc: paulmck@...nel.org, thunder.leizhen@...wei.com,
frederic@...nel.org, joel@...lfernandes.org, rcu@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: Make vmalloc_dump_obj() call in a preemptible
context
On Thu, 17 Nov 2022 19:25:20 +0800 Zqiang <qiang1.zhang@...el.com> wrote:
> Currently, the mem_dump_obj() is invoked in call_rcu(), the
> call_rcu() is maybe invoked in non-preemptive code segment,
> for object allocated from vmalloc(), the following scenarios
> may occur:
>
> CPU 0
> tasks context
> spin_lock(&vmap_area_lock)
> Interrupt context
> call_rcu()
> mem_dump_obj
> vmalloc_dump_obj
> spin_lock(&vmap_area_lock) <--deadlock
>
> and for PREEMPT-RT kernel, the spinlock will convert to sleepable
> lock, so the vmap_area_lock spinlock not allowed to get in non-preemptive
> code segment. therefore, this commit make the vmalloc_dump_obj() call in
> a preemptible context.
>
> ...
>
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -1128,7 +1128,9 @@ void mem_dump_obj(void *object)
> return;
>
> if (virt_addr_valid(object))
> - type = "non-slab/vmalloc memory";
> + type = "non-slab memory";
> + else if (is_vmalloc_addr(object))
> + type = "vmalloc memory";
> else if (object == NULL)
> type = "NULL pointer";
> else if (object == ZERO_SIZE_PTR)
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index ccaa461998f3..018e417b12d6 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -4034,6 +4034,10 @@ bool vmalloc_dump_obj(void *object)
> struct vm_struct *vm;
> void *objp = (void *)PAGE_ALIGN((unsigned long)object);
>
> + if (!is_vmalloc_addr(objp) || ((IS_ENABLED(CONFIG_PREEMPT_RT) &&
> + !preemptible()) || in_interrupt()))
> + return false;
> +
> vm = find_vm_area(objp);
> if (!vm)
> return false;
I suggest this be restructured so we can comment each test:
/* comment goes here */
if (!is_vmalloc_addr(objp))
return false;
/* comment goes here */
if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible())
return false;
/* comment goes here */
if (in_interrupt()))
return false;
Where each comment carefully explains why we're performing the test.
It will generate the same code.
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