Vivek Goyal [off-list ref] writes:
On Tue, Jul 14, 2015 at 05:29:53PM +0000, dwalker@fifo99.com wrote:
[..]
quoted
quoted
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If a machine is failing, there are high chance it can't deliver you the
notification. Detecting that failure suing some kind of polling mechanism
might be more reliable. And it will make even kdump mechanism more
reliable so that it does not have to run panic notifiers after the crash.
I think what your suggesting is that my company should change how it's hardware works
and that's not really an option for me. This isn't a simple thing like checking over the
network if the machine is down or not, this is way more complex hardware design.
That means you are ready to live with an unreliable design. There might be
cases where notifier does not get run properly and you will not do switch
despite the fact that OS has failed. I was just trying to nudge you in
a direction which could be more reliable mechanism.
Sigh I see some deep confusion going on here.
The panic notifiers are just that panic notifiers. They have not been
nor should they be tied to kexec. If those notifiers force a switch
over of between machines I fail to see why you would care if it was
kexec or another panic situation that is forcing that switchover.
Hidehiro isn't fixing the failover situation on my side, he's fixing register
information collection when crash_kexec_post_notifiers is used.
Sure. Given that we have created this new parameter, let us fix it so that
we can capture the other cpu register state in crash dump.
I am little disappointed that it was not tested well when this parameter was
introuced. We should have atleast tested it to the extent to see if there
is proper cpu state present for all cpus in the crash dump.
At that point of time it looked like a simple modification
to allow panic notifiers before crash_kexec().
Either that or we say no one cares enough, and it known broken so let's
just revert the fool thing.
I honestly can't see how to support panic notifiers, before kexec.
There is no way to tell what is being done and all of the pieces
including smp_send_stop are known to be buggy.
It isn't like this latest set of patches was reviewed/tested much
better, as the first patch was wrong.
Eric
On Tue, Jul 14, 2015 at 01:01:12PM -0500, Eric W. Biederman wrote:
Vivek Goyal [off-list ref] writes:
quoted
On Tue, Jul 14, 2015 at 05:29:53PM +0000, dwalker@fifo99.com wrote:
[..]
quoted
quoted
quoted
quoted
quoted
If a machine is failing, there are high chance it can't deliver you the
notification. Detecting that failure suing some kind of polling mechanism
might be more reliable. And it will make even kdump mechanism more
reliable so that it does not have to run panic notifiers after the crash.
I think what your suggesting is that my company should change how it's hardware works
and that's not really an option for me. This isn't a simple thing like checking over the
network if the machine is down or not, this is way more complex hardware design.
That means you are ready to live with an unreliable design. There might be
cases where notifier does not get run properly and you will not do switch
despite the fact that OS has failed. I was just trying to nudge you in
a direction which could be more reliable mechanism.
Sigh I see some deep confusion going on here.
The panic notifiers are just that panic notifiers. They have not been
nor should they be tied to kexec. If those notifiers force a switch
over of between machines I fail to see why you would care if it was
kexec or another panic situation that is forcing that switchover.
Hidehiro isn't fixing the failover situation on my side, he's fixing register
information collection when crash_kexec_post_notifiers is used.
Sure. Given that we have created this new parameter, let us fix it so that
we can capture the other cpu register state in crash dump.
I am little disappointed that it was not tested well when this parameter was
introuced. We should have atleast tested it to the extent to see if there
is proper cpu state present for all cpus in the crash dump.
At that point of time it looked like a simple modification
to allow panic notifiers before crash_kexec().
Either that or we say no one cares enough, and it known broken so let's
just revert the fool thing.
Masami, you introduced this option. Are you fine with the revert? Is it
really being used and tested?
I honestly can't see how to support panic notifiers, before kexec.
There is no way to tell what is being done and all of the pieces
including smp_send_stop are known to be buggy.
we should be able to replace smp_send_stop() with what crash_kexec() is
doing to stop the machine? If yes, then it should be fine I guess. This
parameter description clearly says that specify it at your own risk. So
we are not issuing a big support statement for successful kdump after
panic notifiers. If it is something fixable, otherwise user needs
to deal with it.
Thanks
Vivek
On 2015/07/15 3:23, Vivek Goyal wrote:
On Tue, Jul 14, 2015 at 01:01:12PM -0500, Eric W. Biederman wrote:
quoted
Vivek Goyal [off-list ref] writes:
quoted
On Tue, Jul 14, 2015 at 05:29:53PM +0000, dwalker@fifo99.com wrote:
[..]
quoted
quoted
quoted
quoted
quoted
If a machine is failing, there are high chance it can't deliver you the
notification. Detecting that failure suing some kind of polling mechanism
might be more reliable. And it will make even kdump mechanism more
reliable so that it does not have to run panic notifiers after the crash.
I think what your suggesting is that my company should change how it's hardware works
and that's not really an option for me. This isn't a simple thing like checking over the
network if the machine is down or not, this is way more complex hardware design.
That means you are ready to live with an unreliable design. There might be
cases where notifier does not get run properly and you will not do switch
despite the fact that OS has failed. I was just trying to nudge you in
a direction which could be more reliable mechanism.
Sigh I see some deep confusion going on here.
The panic notifiers are just that panic notifiers. They have not been
nor should they be tied to kexec. If those notifiers force a switch
over of between machines I fail to see why you would care if it was
kexec or another panic situation that is forcing that switchover.
Hidehiro isn't fixing the failover situation on my side, he's fixing register
information collection when crash_kexec_post_notifiers is used.
Sure. Given that we have created this new parameter, let us fix it so that
we can capture the other cpu register state in crash dump.
I am little disappointed that it was not tested well when this parameter was
introuced. We should have atleast tested it to the extent to see if there
is proper cpu state present for all cpus in the crash dump.
At that point of time it looked like a simple modification
to allow panic notifiers before crash_kexec().
Either that or we say no one cares enough, and it known broken so let's
just revert the fool thing.
Masami, you introduced this option. Are you fine with the revert? Is it
really being used and tested?
Actually, it is tested but under very limited situation. I think we
need a clear acceptance criteria, IOW, we need a testset for kdump
so that we can make things better.
Would you have it? maybe we can push it into kselftest.
quoted
I honestly can't see how to support panic notifiers, before kexec.
There is no way to tell what is being done and all of the pieces
including smp_send_stop are known to be buggy.
we should be able to replace smp_send_stop() with what crash_kexec() is
doing to stop the machine? If yes, then it should be fine I guess. This
parameter description clearly says that specify it at your own risk. So
we are not issuing a big support statement for successful kdump after
panic notifiers. If it is something fixable, otherwise user needs
to deal with it.
Agreed (as I've sent in other replay).
Thank you,
--
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@hitachi.com