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>
Summary:
INIT asserted on kdump kernel invokes INIT handler not only on a
cpu that running on the kdump kernel, but also BSP of the panicked
kernel, because the (badly) frozen BSP can be thawed by INIT.
Description:
The kdump_cpu_freeze() is called on cpus except one that initiates
panic and/or kdump, to stop/offline the cpu (on ia64, it means we
pass control of cpus to SAL, or put them in spinloop). Note that
CPU0(BSP) always go to spinloop, so if panic was happened on an AP,
there are at least 2cpus (= the AP and BSP) which not back to SAL.
On the spinning cpus, interrupts are disabled (rsm psr.i), but INIT
is still interruptible because psr.mc for mask them is not set unless
kdump_cpu_freeze() is not called from MCA/INIT context.
Therefore, assume that a panic was happened on an AP, kdump was
invoked, new INIT handlers for kdump kernel was registered and then
an INIT is asserted. From the viewpoint of SAL, there are 2 online
cpus, so INIT will be delivered to both of them. It likely means
that not only the AP (= a cpu executing kdump) enters INIT handler
which is newly registered, but also BSP (= another cpu spinning in
panicked kernel) enters the same INIT handler. Of course setting of
registers in BSP are still old (for panicked kernel), so what happen
with running handler with wrong setting will be extremely unexpected.
I believe this is not desirable behavior.
How to Reproduce:
Start kdump on one of APs (e.g. cpu1)
# taskset 0x2 echo c > /proc/sysrq-trigger
Then assert INIT after kdump kernel is booted, after new INIT handler
for kdump kernel is registered.
Expected results:
An INIT handler is invoked only on the AP.
Actual results:
An INIT handler is invoked on the AP and BSP.
Sample of results:
I got following console log by asserting INIT after prompt "root:/>".
It seems that two monarchs appeared by one INIT, and one panicked at
last. And it also seems that the panicked one supposed there were
4 online cpus and no one did rendezvous:
:
[ 0 %]dropping to initramfs shell
exiting this shell will reboot your system
root:/> Entered OS INIT handler. PSP=fff301a0 cpu=0 monarch=0
ia64_init_handler: Promoting cpu 0 to monarch.
Delaying for 5 seconds...
All OS INIT slaves have reached rendezvous
Processes interrupted by INIT - 0 (cpu 0 task 0xa000000100af0000)
:
<<snip>>
:
Entered OS INIT handler. PSP=fff301a0 cpu=0 monarch=1
Delaying for 5 seconds...
mlogbuf_finish: printing switched to urgent mode, MCA/INIT might be dodgy or fail.
OS INIT slave did not rendezvous on cpu 1 2 3
INIT swapper 0[0]: bugcheck! 0 [1]
:
<<snip>>
:
Kernel panic - not syncing: Attempted to kill the idle task!
Proposed fix:
To avoid this problem, this patch inserts ia64_set_psr_mc() to mask
INIT on cpus going to be frozen. This masking have no effect if the
kdump_cpu_freeze() is called from INIT handler when kdump_on_init == 1,
because psr.mc is already turned on to 1 before entering OS_INIT.
I confirmed that weird log like above are disappeared after applying
this patch.
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>
It is generally agreed that it would be beneficial for u64 to be an
unsigned long long on all architectures. ia64 (in common with several
other 64-bit architectures) currently uses unsigned long. Migrating
piecemeal is too painful; this giant patch fixes all compilation warnings
and errors that come as a result of switching to use int-ll64.h.
Note that userspace will still see __u64 defined as unsigned long. This
is important as it affects C++ name mangling.
[Updated by Tony Luck to change efi.h:efi_freemem_callback_t to use
u64 for start/end rather than unsigned long]
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
After moving the the include files there were a few clean-ups:
1) Some files used #include <asm-ia64/xyz.h>, changed to <asm/xyz.h>
2) Some comments alerted maintainers to look at various header files to
make matching updates if certain code were to be changed. Updated these
comments to use the new include paths.
3) Some header files mentioned their own names in initial comments. Just
deleted these self references.
Signed-off-by: Tony Luck <tony.luck@intel.com>
