[Xen-devel] [PATCH v4 0/2] kexec: Use hypercall_create_continuation to protect KEXEC ops

[Eric DeVolder <eric.devolder@xxxxxxxxxx>]

During testing (using the script below) we found that multiple
invocations of kexec of unload/load are not safe.

This does not exist in classic Xen kernels in which the kexec-tools
did the kexec via Linux kernel syscall (which in turn made the
hypercall), as the Linux code has a mutex_trylock which would
inhibit multiple concurrent calls.

But with the kexec-tools utilizing xc_kexec_* that is no longer
the case and we need to protect against multiple concurrent
invocations.

Please see the patches and review at your convenience!

==== try-crash.pl from bhavesh.davda@xxxxxxxxxx ====
#!/usr/bin/perl -w

use strict;
use warnings;
use threads;

sub threaded_task {
    threads->create(sub {
        my $thr_id = threads->self->tid;
        #print "Starting load thread $thr_id\n";
        system("/sbin/kexec  -p --command-line=\"placeholder 
root=/dev/mapper/nimbula-root ro rhbg console=tty0 console=hvc0 earlyprintk=xen 
nomodeset printk.time=1 irqpoll maxcpus=1 nr_cpus=1 reset_devices 
cgroup_disable=memory mce=off selinux=0 console=ttyS1,115200n8\" 
--initrd=/boot/initrd-4.1.12-61.1.9.el6uek.x86_64kdump.img 
/boot/vmlinuz-4.1.12-61.1.9.el6uek.x86_64");
        #print "Ending load thread $thr_id\n";
        threads->detach(); #End thread.
    });
    threads->create(sub {
        my $thr_id = threads->self->tid;
        #print "Starting unload thread $thr_id\n";
        system("/sbin/kexec  -p -u");
        #print "Ending unload thread $thr_id\n";
        threads->detach(); #End thread.
    });
}

for my $i (0..99)
{
    threaded_task();
}


Eric DeVolder (2):
  kexec: use hypercall_create_continuation to protect KEXEC ops
  kexec: remove spinlock now that all KEXEC hypercall ops are protected
    at the top-level

 xen/common/kexec.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

-- 
2.7.4


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