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    Subject[PATCH v2 09/13] notifier: Show function names on notifier routines if DEBUG_NOTIFIERS is set
    Date
    Currently we have a debug infrastructure in the notifiers file, but
    it's very simple/limited. Extend it by:

    (a) Showing all registered/unregistered notifiers' callback names;

    (b) Adding a dynamic debug tuning to allow showing called notifiers'
    function names. Notice that this should be guarded as a tunable since
    it can flood the kernel log buffer.

    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Cong Wang <xiyou.wangcong@gmail.com>
    Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Valentin Schneider <valentin.schneider@arm.com>
    Cc: Xiaoming Ni <nixiaoming@huawei.com>
    Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>

    ---

    V2:
    - Major improvement thanks to the great idea from Xiaoming - changed
    all the ksym wheel reinvention to printk %ps modifier;

    - Instead of ifdefs, using IS_ENABLED() - thanks Steven.

    - Removed an unlikely() hint on debug path.

    kernel/notifier.c | 22 ++++++++++++++++------
    1 file changed, 16 insertions(+), 6 deletions(-)

    diff --git a/kernel/notifier.c b/kernel/notifier.c
    index 0d5bd62c480e..350761b34f8a 100644
    --- a/kernel/notifier.c
    +++ b/kernel/notifier.c
    @@ -37,6 +37,10 @@ static int notifier_chain_register(struct notifier_block **nl,
    }
    n->next = *nl;
    rcu_assign_pointer(*nl, n);
    +
    + if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS))
    + pr_info("notifiers: registered %ps\n", n->notifier_call);
    +
    return 0;
    }

    @@ -46,6 +50,11 @@ static int notifier_chain_unregister(struct notifier_block **nl,
    while ((*nl) != NULL) {
    if ((*nl) == n) {
    rcu_assign_pointer(*nl, n->next);
    +
    + if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS))
    + pr_info("notifiers: unregistered %ps\n",
    + n->notifier_call);
    +
    return 0;
    }
    nl = &((*nl)->next);
    @@ -77,13 +86,14 @@ static int notifier_call_chain(struct notifier_block **nl,
    while (nb && nr_to_call) {
    next_nb = rcu_dereference_raw(nb->next);

    -#ifdef CONFIG_DEBUG_NOTIFIERS
    - if (unlikely(!func_ptr_is_kernel_text(nb->notifier_call))) {
    - WARN(1, "Invalid notifier called!");
    - nb = next_nb;
    - continue;
    + if (IS_ENABLED(CONFIG_DEBUG_NOTIFIERS)) {
    + if (!func_ptr_is_kernel_text(nb->notifier_call)) {
    + WARN(1, "Invalid notifier called!");
    + nb = next_nb;
    + continue;
    + }
    + pr_debug("notifiers: calling %ps\n", nb->notifier_call);
    }
    -#endif
    ret = nb->notifier_call(nb, val, v);

    if (nr_calls)
    --
    2.37.1
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