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    SubjectRe: [RFC][PATCH] HWPOISON: only early kill processes who installed SIGBUS handler
    On Wed, Jun 17, 2009 at 02:37:02PM +0800, Wu Fengguang wrote:
    > On Mon, Jun 15, 2009 at 10:22:25PM +0800, Wu Fengguang wrote:
    > > On Mon, Jun 15, 2009 at 08:25:28PM +0800, Nick Piggin wrote:
    > > > On Mon, Jun 15, 2009 at 08:10:01PM +0800, Wu Fengguang wrote:
    > > > > On Mon, Jun 15, 2009 at 03:19:07PM +0800, Nick Piggin wrote:
    > > > > > > For KVM you need early kill, for the others it remains to be seen.
    > > > > >
    > > > > > Right. It's almost like you need to do a per-process thing, and
    > > > > > those that can handle things (such as the new SIGBUS or the new
    > > > > > EIO) could get those, and others could be killed.
    > > > >
    > > > > To send early SIGBUS kills to processes who has called
    > > > > sigaction(SIGBUS, ...)? KVM will sure do that. For other apps we
    > > > > don't mind they can understand that signal at all.
    > > >
    > > > For apps that hook into SIGBUS for some other means and
    > >
    > > Yes I was referring to the sigaction(SIGBUS) apps, others will
    > > be late killed anyway.
    > >
    > > > do not understand the new type of SIGBUS signal? What about
    > > > those?
    > >
    > > We introduced two new SIGBUS codes:
    > > BUS_MCEERR_AO=5 for early kill
    > > BUS_MCEERR_AR=4 for late kill
    > > I'd assume a legacy application will handle them in the same way (both
    > > are unexpected code to the application).
    > >
    > > We don't care whether the application can be killed by BUS_MCEERR_AO
    > > or BUS_MCEERR_AR depending on its SIGBUS handler implementation.
    > > But (in the rare case) if the handler
    > > - refused to die on BUS_MCEERR_AR, it may create a busy loop and
    > > flooding of SIGBUS signals, which is a bug of the application.
    > > BUS_MCEERR_AO is one time and won't lead to busy loops.
    > > - does something that hurts itself (ie. data safety) on BUS_MCEERR_AO,
    > > it may well hurt the same way on BUS_MCEERR_AR. The latter one is
    > > unavoidable, so the application must be fixed anyway.
    >
    > This patch materializes the automatically early kill idea.
    > It aims to remove the vm.memory_failure_ealy_kill sysctl parameter.
    >
    > This is mainly a policy change, please comment.

    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?



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