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x86/xen: Return from panic notifier 

Currently execution of panic() continues until Xen's panic notifier
(xen_panic_event()) is called at which point we make a hypercall that
never returns.

This means that any notifier that is supposed to be called later as
well as significant part of panic() code (such as pstore writes from
kmsg_dump()) is never executed.

There is no reason for xen_panic_event() to be this last point in
execution since panic()'s emergency_restart() will call into
xen_emergency_restart() from where we can perform our hypercall.

Nevertheless, we will provide xen_legacy_crash boot option that will
preserve original behavior during crash. This option could be used,
for example, if running kernel dumper (which happens after panic
notifiers) is undesirable.

Reported-by: James Dingwall <james@dingwall.me.uk>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
This commit is contained in:
Boris Ostrovsky 2019-09-30 16:44:41 -04:00
parent a8fabb3852
commit c6875f3aac
2 changed files with 29 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
Documentation/admin-guide/kernel-parameters.txt
View File

@ -5267,6 +5267,10 @@
the unplug protocol
never -- do not unplug even if version check succeeds
xen_legacy_crash [X86,XEN]
Crash from Xen panic notifier, without executing late
panic() code such as dumping handler.
xen_nopvspin [X86,XEN]
Disables the ticketlock slowpath using Xen PV
optimizations.

28
arch/x86/xen/enlighten.c
View File

@ -269,19 +269,41 @@ void xen_reboot(int reason)
BUG();
}
static int reboot_reason = SHUTDOWN_reboot;
static bool xen_legacy_crash;
void xen_emergency_restart(void)
{
xen_reboot(SHUTDOWN_reboot);
xen_reboot(reboot_reason);
}
static int
xen_panic_event(struct notifier_block *this, unsigned long event, void *ptr)
{
if (!kexec_crash_loaded())
xen_reboot(SHUTDOWN_crash);
if (!kexec_crash_loaded()) {
if (xen_legacy_crash)
xen_reboot(SHUTDOWN_crash);
reboot_reason = SHUTDOWN_crash;
/*
* If panic_timeout==0 then we are supposed to wait forever.
* However, to preserve original dom0 behavior we have to drop
* into hypervisor. (domU behavior is controlled by its
* config file)
*/
if (panic_timeout == 0)
panic_timeout = -1;
}
return NOTIFY_DONE;
}
static int __init parse_xen_legacy_crash(char *arg)
{
xen_legacy_crash = true;
return 0;
}
early_param("xen_legacy_crash", parse_xen_legacy_crash);
static struct notifier_block xen_panic_block = {
.notifier_call = xen_panic_event,
.priority = INT_MIN