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    SubjectRe: [RFC][PATCH] HWPOISON: only early kill processes who installed SIGBUS handler
    On Wed, Jun 17, 2009 at 06:00:06PM +0800, Nick Piggin wrote:
    > On Wed, Jun 17, 2009 at 05:55:32PM +0800, Wu Fengguang wrote:
    > > On Wed, Jun 17, 2009 at 04:04:04PM +0800, Nick Piggin wrote:
    > > > Well then you can still early-kill random apps that did not
    > > > want it, and you may still cause problems if its sigbus
    > > > handler does something nontrivial.
    > > >
    > > > Can you use a prctl or something so it can expclitly
    > > > register interest in this?
    > >
    > > No I don't think prctl would be much better.
    > >
    > > - if an application want early/late kill, it can do so with a proper
    > > written SIGBUS handler: the prctl call is redundant.
    > s/proper written/is switched to new semantics based on the existance
    > of a/

    Not necessarily so. If an application
    - did not has a SIGBUS handler, and want to be
    - early killed: must install a handler, this is not a big problem
    because it may well want to rescue something on the event.
    - late killed: just do nothing.
    (here kill = 'notification')
    - had a SIGBUS hander, and want to
    - early die: call exit(0) in the handler.
    - late die: intercept and ignore the signal.
    So if source code modification is viable, prctl is not necessary at all.

    > > - if an admin want to control early/late kill for an unmodified app,
    > > prctl is as unhelpful as this patch(*).
    > Clearly you can execute a process with a given prctl.

    OK, right.

    > > - prctl does can help legacy apps whose SIGBUS handler has trouble
    > > with the new SIGBUS codes, however such application should be rare
    > > and the application should be fixed(why shall it do something wrong
    > > on newly introduced code at all? Shall we stop introducing new codes
    > > just because some random buggy app cannot handle new codes?)
    > Backwards compatibility? Kind of important.


    > > So I still prefer this patch, until we come up with some solution that
    > > allows both app and admin to change the setting.
    > Not only does it allow that, but it also provides backwards
    > compatibility. Your patch does not allow admin to change
    > anything nor does it guarantee 100% back compat so I can't
    > see how you think it is better.

    I didn't say it is better, but clearly mean that prctl is not better
    enough to warrant a new user interface, if(!adm_friendly). Now it's
    obvious that adm_friendly=1, so I agree prctl is a good interface :)

    > Also it does not allow for an app with a SIGBUS handler to
    > use late kill. If late kill is useful to anyone, why would
    > it not be useful to some app with a SIGBUS handler (that is
    > not KVM)?

    Late kill will always be sent. Ignore the early kill signal in the
    SIGBUS handler does the trick (see above analyzes).


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