Re: [Xen-devel] [PATCH] kexec: clear kexec_image slot when unloading kexec image

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 03.04.17 at 19:44, <bhavesh.davda@xxxxxxxxxx> wrote:
> While theoretically this bug can be tickled simply by a sequence of 'kexec -p'
> to load a kexec crash image followed by two back-to-back 'kexec -p -u' to
> unload the kexec crash image, I found the following perl script to be useful 
> to
> reliably reproduce Xen panics as well as verify that the fix works. YMMV.
> 
> -snip-
> #!/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/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.x86_64kdump.img /boot/vmlinuz.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();
> }
> -snip-
> 
> ---

Looks like you've mixed up commit message (everything up from this
marker) and ...

> When kexec_do_unload calls kexec_swap_images to get the old kexec_image to
> free, it passes NULL for the new kexec_image pointer. The new slot wasn't 
> being
> cleared in such a case, leading to a stale pointer being left behind in the
> kexec_image array and Xen panics in subsequent load/unload operations.
> 
> Signed-off-by: Bhavesh Davda <bhavesh.davda@xxxxxxxxxx>
> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Reviewed-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>

... auxiliary information (after the first --- marker).

Other than that
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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