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    Subject[PATCH] Kprobes: Fix deadlock in function-return probes
    From: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

    When two function-return probes are inserted on kfree()[1] and the
    second on say, sys_link()[2], and later [2] is unregistered, we have
    a deadlock as kfree is called with the kretprobe_lock held and the
    function-return probe on kfree will also try to grab the same lock.

    However, we can move the kfree() during unregistration to outside
    the spinlock as we are sure that no instances from the free list
    will be used after synchronized_sched() returns during the
    unregistration process. Thanks to Masami Hiramatsu for spotting this.

    Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    ---


    kernel/kprobes.c | 2 +-
    1 files changed, 1 insertion(+), 1 deletion(-)

    Index: linux-2.6.16-rc1/kernel/kprobes.c
    ===================================================================
    --- linux-2.6.16-rc1.orig/kernel/kprobes.c
    +++ linux-2.6.16-rc1/kernel/kprobes.c
    @@ -631,12 +631,12 @@ void __kprobes unregister_kretprobe(stru
    unregister_kprobe(&rp->kp);
    /* No race here */
    spin_lock_irqsave(&kretprobe_lock, flags);
    - free_rp_inst(rp);
    while ((ri = get_used_rp_inst(rp)) != NULL) {
    ri->rp = NULL;
    hlist_del(&ri->uflist);
    }
    spin_unlock_irqrestore(&kretprobe_lock, flags);
    + free_rp_inst(rp);
    }

    static int __init init_kprobes(void)
    -
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