Subject: Re: struct dev_pagemap corruption

From: Jerome Glisse <[email-masked]>
Date: Fri, 5 Apr 2019 09:53:24 -0400

On Fri, Apr 05, 2019 at 10:10:22AM +0530, Anshuman Khandual wrote:
> Hello,
> 
> On arm64 platform "struct dev_pagemap" is getting corrupted during ZONE_DEVICE
> unmapping path through device_destroy(). Its device memory range end address
> (pgmap->res.end) which is getting corrupted in this particular case. AFAICS
> pgmap which gets initialized by the driver and mapped with devm_memremap_pages()
> should retain it's values during the unmapping path as well. Is this assumption
> right ?
> 
> [   62.779412] Call trace:
> [   62.779808]  dump_backtrace+0x0/0x118
> [   62.780460]  show_stack+0x14/0x20
> [   62.781204]  dump_stack+0xa8/0xcc
> [   62.781941]  devm_memremap_pages_release+0x24/0x1d8
> [   62.783021]  devm_action_release+0x10/0x18
> [   62.783911]  release_nodes+0x1b0/0x220
> [   62.784732]  devres_release_all+0x34/0x50
> [   62.785623]  device_release+0x24/0x90
> [   62.786454]  kobject_put+0x74/0xe8
> [   62.787214]  device_destroy+0x48/0x58
> [   62.788041]  zone_device_public_altmap_init+0x404/0x42c [zone_device_public_altmap]
> [   62.789675]  do_one_initcall+0x74/0x190
> [   62.790528]  do_init_module+0x50/0x1c0
> [   62.791346]  load_module+0x1be4/0x2140
> [   62.792192]  __se_sys_finit_module+0xb8/0xc8
> [   62.793128]  __arm64_sys_finit_module+0x18/0x20
> [   62.794128]  el0_svc_handler+0x88/0x100
> [   62.794989]  el0_svc+0x8/0xc
> 
> The problem can be traced down here.
> 
> diff --git a/drivers/base/devres.c b/drivers/base/devres.c
> index e038e2b3b7ea..2a410c88c596 100644
> --- a/drivers/base/devres.c
> +++ b/drivers/base/devres.c
> @@ -33,7 +33,7 @@ struct devres {
>          * Thus we use ARCH_KMALLOC_MINALIGN here and get exactly the same
>          * buffer alignment as if it was allocated by plain kmalloc().
>          */
> -       u8 __aligned(ARCH_KMALLOC_MINALIGN) data[];
> +       u8 __aligned(__alignof__(unsigned long long)) data[];
>  };

I doubt that pgmap->res.end get corrupted during device_destroy() but given
that the above changes fix the issue it kind of boggle the mind. If i where
to debug this i would probably run a kernel with qemu -s to get a gdbserver
and then attach gdb and set breakpoint on devm_memremap_pages() then when
that trigger i would set memory watch on the pgmap->res.end (there use to be
way to use memory as pmem through kernel boot option).

A printk alternative solution is, assuming you only have one pgmap, add a
global static struct pgmap *debug_pgmap = NULL; in memremap.c set that in
devm_memremap_pages() and add an helper function:

void debug_pgmap(const char *file, unsigned line)
{
    printk(... file, line);
    printk(... debug_pmap->res.end);
}

In a header:
#define DEBUG_PGMAP debug_pgmap(__FILE__, __LINE__);

Then sprinkle DEBUG_PGMAP within device_destroy(), device_unregister(),
device_release() and see when it get corrupted.

gdb would be faster but sometime i got issue with memory watchpoint and virt.

Cheers,
Jérôme

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