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

[Masami Hiramatsu]

On Tue, 14 Jan 2020 08:56:21 -0500
Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote:

> 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@xxxxxxxxxxxxxxxxx>

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

OK, I'll update it on the latest -tip with your reviewed-by.

Thank you,

> 
> thanks,
> 
>  - Joel
> 
> 
> > 
> > Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> > ---
> >  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) {
> > 


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>