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    SubjectRe: [patch 1/8] Kprobes - do not use kprobes mutex in arch code
    On Sat, Jul 14, 2007 at 03:20:02PM -0400, Mathieu Desnoyers wrote:
    > * Christoph Hellwig (hch@infradead.org) wrote:
    > > On Fri, Jul 13, 2007 at 09:21:34PM -0400, Mathieu Desnoyers wrote:
    > > > Remove the kprobes mutex from kprobes.h, since it does not belong there. Also
    > > > remove all use of this mutex in the architecture specific code, replacing it by
    > > > a proper mutex lock/unlock in the architecture agnostic code.
    > >
    > > This is not very nice for avr32/sparc64 which have a noop arch_remove_kprobe
    > > and now need to take a mutex to do nothing. Maybe you can find a nice
    > > way to avoid that?
    > >
    > > Except for this issue making kprobes_mutex static to kprobes.c sounds like
    > > a good improvement.
    > >
    >
    > Since only unregister_kprobe() calls arch_remove_kprobe(), and only
    > after having removed the struct kprobe from the kprobes list (while the
    > kprobes mutex is held), I wonder if there is any need to hold the
    > kprobes mutex at all when calling arch_remove_kprobe(). It turns out
    > that only get_insn_slot()/free_insn_slot() (which is in
    > kernel/kprobes.c, but called from arch specific code) seems to really
    > use protection of this mutex.

    Right.

    > Would it make sense to protect the kprobe_insn_pages list with a
    > new kprobe_insn_mutex, nestable in the kprobe_mutex ?

    Do you think it is required after your change to make kprobe_mutex
    static? But yes, for architectures that don't need a arch_remove_kprobe,
    the situation is a bit odd... a mutex to do nothing. IIRC, that was the
    primary reason why we made the mutex visible outside of kernel/kprobes.c

    Ananth
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