Re: [LKP] Re: [mm/vunmap] e47110e905: WARNING:at_mm/vmalloc.c:#__vunmap

From: Xing Zhengjun
Date: Wed Apr 28 2021 - 04:32:48 EST

Hi Linus,

On 4/24/2021 1:18 AM, Linus Torvalds wrote:
On Thu, Apr 22, 2021 at 11:15 PM kernel test robot
<oliver.sang@xxxxxxxxx> wrote:

commit: e47110e90584a22e9980510b00d0dfad3a83354e ("mm/vunmap: add cond_resched() in vunmap_pmd_range")

Funky. That commit doesn't seem to have anything to do with the oops.

The oops is odd too:

[ 198.731223] WARNING: CPU: 0 PID: 1948 at mm/vmalloc.c:2247 __vunmap (kbuild/src/consumer/mm/vmalloc.c:2247 (discriminator 1))

That's the warning for an unaligned vunmap():

2247 if (WARN(!PAGE_ALIGNED(addr), "Trying to vfree() bad
address (%p)\n",
2248 addr))
2249 return;

[ 198.744933] Call Trace:
[ 198.745229] free_module (kbuild/src/consumer/kernel/module.c:2251)

2248 /* This may be empty, but that's OK */
2249 module_arch_freeing_init(mod);
2250 module_memfree(mod->init_layout.base);

We add debug code to print logs when mod->init_layout.base is NULL, after more than 100 times test, we find that when mod->init_layout.base is NULL, no align warning happened. From the descriptions of vfree, if @addr is NULL, no operation is performed. So when the warning happened, the mod->init_layout.base is not a NULL.

void vfree(const void *addr)



if (!addr)


static void __vfree(const void *addr)
if (unlikely(in_interrupt()))
__vunmap(addr, 1);

2251 kfree(mod->args);

That's the "module_memfree()" - the return address points to the
return point, which is the next line.

And as far as I can tell, the only thing that assigns anything but
NULL to that init_layout.base is

ptr = module_alloc(mod->init_layout.size);

which uses __vmalloc_node_range() for the allocation.

So absolutely nothing in this report makes sense to me. I suspect it's
some odd memory corruption.

Oliver - how reliable is that bisection?

Does anybody else see what might be up?

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Zhengjun Xing