Re: [PATCH -tip V2 2/2] kprobes: Use non RCU traversal APIs on kprobe_tables if possible

[Joel Fernandes <joel@joelfernandes.org>]

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) {
>