kdump/kexec kernel
Summary:
Asserting INIT on the beginning of kdump/kexec kernel will result
in unexpected behavior because INIT handler for previous kernel is
invoked on new kernel.
Description:
In panic situation, we can receive INIT while kernel transition,
i.e. from beginning of panic to bootstrap of kdump kernel.
Since we initialize registers on leave from current kernel, no
longer monarch/slave handlers of current kernel in virtual mode are
called safely. (In fact system goes hang as far as I confirmed)
How to Reproduce:
Start kdump
# echo c > /proc/sysrq-trigger
Then assert INIT while kdump kernel is booting, before new INIT
handler for kdump kernel is registered.
Expected(Desirable) result:
kdump kernel boots without any problem, crashdump retrieved
Actual result:
INIT handler for previous kernel is invoked on kdump kernel
=> panic, hang etc. (unexpected)
Proposed fix:
We can unregister these init handlers from SAL before jumping into
new kernel, however then the INIT will fallback to default behavior,
result in warmboot by SAL (according to the SAL specification) and
we cannot retrieve the crashdump.
Therefore this patch introduces a NOP init handler and register it
to SAL before leave from current kernel, to start kdump safely by
preventing INITs from entering virtual mode and resulting in warmboot.
On the other hand, in case of kexec that not for kdump, it also
has same problem with INIT while kernel transition.
This patch handles this case differently, because for kexec
unregistering handlers will be preferred than registering NOP
handler, since the situation "no handlers registered" is usual
state for kernel's entry.
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Haren Myneni <hbabu@us.ibm.com>
Cc: kexec@lists.infradead.org
Acked-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
07a6a4ae82