linux-kernel - Re: [PATCH 1/3 v4] x86/kdump: always reserve the low 1MiB when the crashkernel option is specified

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Message-ID: <1789830883.7797936.1571751834645.JavaMail.zimbra@redhat.com>
Date:   Tue, 22 Oct 2019 09:43:54 -0400 (EDT)
From:   Dave Anderson <anderson@...hat.com>
To:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3 v4] x86/kdump: always reserve the low 1MiB when the
 crashkernel option is specified


---- Original Message -----

> > 
> > [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 values
> > 
> >       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)
> > 
> > crash> kmem -s|grep -i invalid
> > kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid freepointer:a6086ac099f0c5a4
> > kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid freepointer:a6086ac099f0c5a4
> > crash>
> 
> 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