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Date:   Tue, 22 Oct 2019 09:43:54 -0400 (EDT)
From:   Dave Anderson <anderson@redhat.com>
To:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Subject: Re: [PATCH 1/3 v4] x86/kdump: always reserve the low 1MiB when the
 crashkernel option is specified
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Thread-Topic: x86/kdump: always reserve the low 1MiB when the crashkernel option is specified
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---- Original Message -----

> >=20
> > [root linux]$ crash vmlinux
> > /var/crash/127.0.0.1-2019-09-19-08\:31\:27/vmcore
> > WARNING: kernel relocated [240MB]: patching 97110 gdb minimal_symbol va=
lues
> >=20
> >       KERNEL: /var/crash/127.0.0.1-2019-09-19-08:31:27/vmlinux
> >     DUMPFILE: /var/crash/127.0.0.1-2019-09-19-08:31:27/vmcore  [PARTIAL=
 DUMP]
> >         CPUS: 128
> >         DATE: Thu Sep 19 08:31:18 2019
> >       UPTIME: 00:01:21
> > LOAD AVERAGE: 0.16, 0.07, 0.02
> >        TASKS: 1343
> >     NODENAME: amd-ethanol
> >      RELEASE: 5.3.0-rc7+
> >      VERSION: #4 SMP Thu Sep 19 08:14:00 EDT 2019
> >      MACHINE: x86_64  (2195 Mhz)
> >       MEMORY: 127.9 GB
> >        PANIC: "Kernel panic - not syncing: sysrq triggered crash"
> >          PID: 9789
> >      COMMAND: "bash"
> >         TASK: "ffff89711894ae80  [THREAD_INFO: ffff89711894ae80]"
> >          CPU: 83
> >        STATE: TASK_RUNNING (PANIC)
> >=20
> > crash> kmem -s|grep -i invalid
> > kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid freepointer:a6086a=
c099f0c5a4
> > kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid freepointer:a6086a=
c099f0c5a4
> > crash>
>=20
> I fail to see what that's trying to tell me? You have invalid pointers?

Correct, because the pointer values are encrypted.  The command is walking =
through the
singly-linked list of free objects in a slab from the dma-kmalloc-512 slab =
cache.  The
slab memory had been allocated from low memory, and because of the  problem=
 at hand,
it was was copied to the vmcore in its encrypted state.

Dave=20