linux-kernel - Re: kmemleak panic

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Date:   Sat, 19 Jan 2019 13:28:33 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Marc Gonzalez <marc.w.gonzalez@...e.fr>
Cc:     Robin Murphy <robin.murphy@....com>,
        Mark Rutland <mark.rutland@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Oscar Salvador <osalvador@...e.de>,
        Wei Yang <richard.weiyang@...il.com>,
        Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sri Krishna chowdary <schowdary@...dia.com>,
        Qian Cai <cai@....pw>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: kmemleak panic

On Fri, Jan 18, 2019 at 04:36:59PM +0100, Marc Gonzalez wrote:
> mount -t debugfs nodev /sys/kernel/debug/ 
> echo scan > /sys/kernel/debug/kmemleak
> 
> Unable to handle kernel paging request at virtual address ffffffc021e00000
[...]
> Call trace:
>  scan_block+0x70/0x190
>  scan_gray_list+0x108/0x1c0
>  kmemleak_scan+0x33c/0x7c0
>  kmemleak_write+0x410/0x4b0

As per Robin's remark, this address seems to be pretty easy to
reproduce. It also happens via scan_gray_list() which indicates an
object kmemleak was informed about via kmemleak_alloc() (so this
excludes the pfn that Qian noticed).

Can you configure the kernel with CONFIG_DEBUG_KMEMLEAK_AUTO_SCAN off
just to avoid the bug being triggered early and run:

  mount -t debugfs nodev /sys/kernel/debug/
  echo dump=0xffffffc021e00000 > /sys/kernel/debug/kmemleak

Then run another scan to make sure this is the address that triggered
the page fault:

  echo scan > /sys/kernel/debug/kmemleak

The above should tell us where the object that kmemleak is trying to
scan came from.

Of course, ideally we should bisect this but I haven't been able to
reproduce it.

-- 
Catalin