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    SubjectRe: [PATCH 3/8] jump label: Fix error with preempt disable holding mutex
    (2010/10/28 22:55), Steven Rostedt wrote:
    > From: Steven Rostedt <srostedt@redhat.com>
    >
    > Kprobes and jump label were having a race between mutexes that
    > was fixed by reordering the jump label. But this reordering
    > moved the jump label mutex into a preempt disable location.
    >
    > This patch does a little fiddling to move the grabbing of
    > the jump label mutex from inside the preempt disable section
    > and still keep the order correct between the mutex and the
    > kprobes lock.

    Ah, right. Thank you for fixing it.

    Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

    >
    > Reported-by: Ingo Molnar <mingo@elte.hu>
    > Cc: Jason Baron <jbaron@redhat.com>
    > Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    > Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    > ---
    > kernel/kprobes.c | 26 +++++++++++++-------------
    > 1 files changed, 13 insertions(+), 13 deletions(-)
    >
    > diff --git a/kernel/kprobes.c b/kernel/kprobes.c
    > index 9437e14..9737a76 100644
    > --- a/kernel/kprobes.c
    > +++ b/kernel/kprobes.c
    > @@ -1145,17 +1145,13 @@ int __kprobes register_kprobe(struct kprobe *p)
    > if (ret)
    > return ret;
    >
    > - preempt_disable();
    > jump_label_lock();
    > + preempt_disable();
    > if (!kernel_text_address((unsigned long) p->addr) ||
    > in_kprobes_functions((unsigned long) p->addr) ||
    > ftrace_text_reserved(p->addr, p->addr) ||
    > - jump_label_text_reserved(p->addr, p->addr)) {
    > - preempt_enable();
    > - jump_label_unlock();
    > - return -EINVAL;
    > - }
    > - jump_label_unlock();
    > + jump_label_text_reserved(p->addr, p->addr))
    > + goto fail_with_jump_label;
    >
    > /* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
    > p->flags &= KPROBE_FLAG_DISABLED;
    > @@ -1169,10 +1165,9 @@ int __kprobes register_kprobe(struct kprobe *p)
    > * We must hold a refcount of the probed module while updating
    > * its code to prohibit unexpected unloading.
    > */
    > - if (unlikely(!try_module_get(probed_mod))) {
    > - preempt_enable();
    > - return -EINVAL;
    > - }
    > + if (unlikely(!try_module_get(probed_mod)))
    > + goto fail_with_jump_label;
    > +
    > /*
    > * If the module freed .init.text, we couldn't insert
    > * kprobes in there.
    > @@ -1180,11 +1175,11 @@ int __kprobes register_kprobe(struct kprobe *p)
    > if (within_module_init((unsigned long)p->addr, probed_mod) &&
    > probed_mod->state != MODULE_STATE_COMING) {
    > module_put(probed_mod);
    > - preempt_enable();
    > - return -EINVAL;
    > + goto fail_with_jump_label;
    > }
    > }
    > preempt_enable();
    > + jump_label_unlock();
    >
    > p->nmissed = 0;
    > INIT_LIST_HEAD(&p->list);
    > @@ -1226,6 +1221,11 @@ out:
    > module_put(probed_mod);
    >
    > return ret;
    > +
    > +fail_with_jump_label:
    > + preempt_enable();
    > + jump_label_unlock();
    > + return -EINVAL;
    > }
    > EXPORT_SYMBOL_GPL(register_kprobe);
    >


    --
    Masami HIRAMATSU
    2nd Dept. Linux Technology Center
    Hitachi, Ltd., Systems Development Laboratory
    E-mail: masami.hiramatsu.pt@hitachi.com


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