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SubjectRe: [PATCH -tip V2 2/2] kprobes: Use non RCU traversal APIs on kprobe_tables if possible
On Tue, Dec 03, 2019 at 03:06:28PM +0900, Masami Hiramatsu wrote:
> Current kprobes uses RCU traversal APIs on kprobe_tables
> even if it is safe because kprobe_mutex is locked.
>
> Make those traversals to non-RCU APIs where the kprobe_mutex
> is locked.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>

May be resend both patch with appropriate tags since it has been some time
since originally posted?

thanks,

- Joel


>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
> ---
> kernel/kprobes.c | 29 ++++++++++++++++++++---------
> 1 file changed, 20 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index f9ecb6d532fb..4caab01ace30 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -46,6 +46,11 @@
>
>
> static int kprobes_initialized;
> +/* kprobe_table can be accessed by
> + * - Normal hlist traversal and RCU add/del under kprobe_mutex is held.
> + * Or
> + * - RCU hlist traversal under disabling preempt (breakpoint handlers)
> + */
> static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
> static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
>
> @@ -829,7 +834,7 @@ static void optimize_all_kprobes(void)
> kprobes_allow_optimization = true;
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> - hlist_for_each_entry_rcu(p, head, hlist)
> + hlist_for_each_entry(p, head, hlist)
> if (!kprobe_disabled(p))
> optimize_kprobe(p);
> }
> @@ -856,7 +861,7 @@ static void unoptimize_all_kprobes(void)
> kprobes_allow_optimization = false;
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> - hlist_for_each_entry_rcu(p, head, hlist) {
> + hlist_for_each_entry(p, head, hlist) {
> if (!kprobe_disabled(p))
> unoptimize_kprobe(p, false);
> }
> @@ -1479,12 +1484,14 @@ static struct kprobe *__get_valid_kprobe(struct kprobe *p)
> {
> struct kprobe *ap, *list_p;
>
> + lockdep_assert_held(&kprobe_mutex);
> +
> ap = get_kprobe(p->addr);
> if (unlikely(!ap))
> return NULL;
>
> if (p != ap) {
> - list_for_each_entry_rcu(list_p, &ap->list, list)
> + list_for_each_entry(list_p, &ap->list, list)
> if (list_p == p)
> /* kprobe p is a valid probe */
> goto valid;
> @@ -1649,7 +1656,9 @@ static int aggr_kprobe_disabled(struct kprobe *ap)
> {
> struct kprobe *kp;
>
> - list_for_each_entry_rcu(kp, &ap->list, list)
> + lockdep_assert_held(&kprobe_mutex);
> +
> + list_for_each_entry(kp, &ap->list, list)
> if (!kprobe_disabled(kp))
> /*
> * There is an active probe on the list.
> @@ -1728,7 +1737,7 @@ static int __unregister_kprobe_top(struct kprobe *p)
> else {
> /* If disabling probe has special handlers, update aggrprobe */
> if (p->post_handler && !kprobe_gone(p)) {
> - list_for_each_entry_rcu(list_p, &ap->list, list) {
> + list_for_each_entry(list_p, &ap->list, list) {
> if ((list_p != p) && (list_p->post_handler))
> goto noclean;
> }
> @@ -2042,13 +2051,15 @@ static void kill_kprobe(struct kprobe *p)
> {
> struct kprobe *kp;
>
> + lockdep_assert_held(&kprobe_mutex);
> +
> p->flags |= KPROBE_FLAG_GONE;
> if (kprobe_aggrprobe(p)) {
> /*
> * If this is an aggr_kprobe, we have to list all the
> * chained probes and mark them GONE.
> */
> - list_for_each_entry_rcu(kp, &p->list, list)
> + list_for_each_entry(kp, &p->list, list)
> kp->flags |= KPROBE_FLAG_GONE;
> p->post_handler = NULL;
> kill_optimized_kprobe(p);
> @@ -2217,7 +2228,7 @@ static int kprobes_module_callback(struct notifier_block *nb,
> mutex_lock(&kprobe_mutex);
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> - hlist_for_each_entry_rcu(p, head, hlist)
> + hlist_for_each_entry(p, head, hlist)
> if (within_module_init((unsigned long)p->addr, mod) ||
> (checkcore &&
> within_module_core((unsigned long)p->addr, mod))) {
> @@ -2468,7 +2479,7 @@ static int arm_all_kprobes(void)
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> /* Arm all kprobes on a best-effort basis */
> - hlist_for_each_entry_rcu(p, head, hlist) {
> + hlist_for_each_entry(p, head, hlist) {
> if (!kprobe_disabled(p)) {
> err = arm_kprobe(p);
> if (err) {
> @@ -2511,7 +2522,7 @@ static int disarm_all_kprobes(void)
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> /* Disarm all kprobes on a best-effort basis */
> - hlist_for_each_entry_rcu(p, head, hlist) {
> + hlist_for_each_entry(p, head, hlist) {
> if (!arch_trampoline_kprobe(p) && !kprobe_disabled(p)) {
> err = disarm_kprobe(p, false);
> if (err) {
>

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