linux-kernel - Re: 32-bit Amlogic (ARM) SoC: kernel BUG in kfree()

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Date:   Thu, 21 Mar 2019 14:44:01 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, akpm@...ux-foundation.org,
        mhocko@...e.com, rppt@...ux.ibm.com,
        linux-amlogic@...ts.infradead.org, liang.yang@...ogic.com,
        linux@...linux.org.uk, linux-mtd@...ts.infradead.org
Subject: Re: 32-bit Amlogic (ARM) SoC: kernel BUG in kfree()

On Thu, Mar 21, 2019 at 09:17:34PM +0100, Martin Blumenstingl wrote:
> Hello,
> 
> I am experiencing the following crash:
>   ------------[ cut here ]------------
>   kernel BUG at mm/slub.c:3950!

        if (unlikely(!PageSlab(page))) {
                BUG_ON(!PageCompound(page));

You called kfree() on the address of a page which wasn't allocated by slab.

> I have traced this crash to the kfree() in meson_nfc_read_buf().
> my observation is as follows:
> - meson_nfc_read_buf() is called 7 times without any crash, the
> kzalloc() call returns 0xe9e6c600 (virtual address) / 0x29e6c600
> (physical address)
> - the eight time meson_nfc_read_buf() is called kzalloc() call returns
> 0xee39a38b (virtual address) / 0x2e39a38b (physical address) and the
> final kfree() crashes
> - changing the size in the kzalloc() call from PER_INFO_BYTE (= 8) to
> PAGE_SIZE works around that crash

I suspect you're doing something which corrupts memory.  Overrunning
the end of your allocation or something similar.  Have you tried KASAN
or even the various slab debugging (eg redzones)?