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Message-ID: <CADxym3bYjj0ecuce3HaOihks3AU5fEmOKvC3FNzbK=cpu6+RoQ@mail.gmail.com>
Date: Tue, 19 Aug 2025 10:26:22 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Jiri Olsa <olsajiri@...il.com>, rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
hca@...ux.ibm.com, revest@...omium.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 1/4] fprobe: use rhltable for fprobe_ip_table
On Tue, Aug 19, 2025 at 10:11 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Mon, 18 Aug 2025 15:43:44 +0200
> Jiri Olsa <olsajiri@...il.com> wrote:
>
> > On Sun, Aug 17, 2025 at 10:46:02AM +0800, Menglong Dong wrote:
> >
> > SNIP
> >
> > > +/* Node insertion and deletion requires the fprobe_mutex */
> > > +static int insert_fprobe_node(struct fprobe_hlist_node *node)
> > > +{
> > > lockdep_assert_held(&fprobe_mutex);
> > >
> > > - next = find_first_fprobe_node(ip);
> > > - if (next) {
> > > - hlist_add_before_rcu(&node->hlist, &next->hlist);
> > > - return;
> > > - }
> > > - head = &fprobe_ip_table[hash_ptr((void *)ip, FPROBE_IP_HASH_BITS)];
> > > - hlist_add_head_rcu(&node->hlist, head);
> > > + return rhltable_insert(&fprobe_ip_table, &node->hlist, fprobe_rht_params);
> > > }
> > >
> > > /* Return true if there are synonims */
> > > @@ -92,9 +92,11 @@ static bool delete_fprobe_node(struct fprobe_hlist_node *node)
> > > /* Avoid double deleting */
> > > if (READ_ONCE(node->fp) != NULL) {
> > > WRITE_ONCE(node->fp, NULL);
> > > - hlist_del_rcu(&node->hlist);
> > > + rhltable_remove(&fprobe_ip_table, &node->hlist,
> > > + fprobe_rht_params);
> > > }
> > > - return !!find_first_fprobe_node(node->addr);
> > > + return !!rhltable_lookup(&fprobe_ip_table, &node->addr,
> > > + fprobe_rht_params);
> >
> > I think rhltable_lookup needs rcu lock
>
> Good catch! Hmm, previously we guaranteed that the find_first_fprobe_node()
> must be called under rcu read locked or fprobe_mutex locked, so that the
> node list should not be changed. But according to the comment of
> rhltable_lookup(), we need to lock the rcu_read_lock() around that.
Hmm, I thought that we don't need the rcu_read_lock() when we hold
fprobe_mutex. It seems that the thing is not as simple as I thought.
I'll split this patch out and send a V6 with this modification.
Thanks!
Menglong Dong
>
> >
> > > }
> > >
> > > /* Check existence of the fprobe */
> > > @@ -249,9 +251,10 @@ static inline int __fprobe_kprobe_handler(unsigned long ip, unsigned long parent
> > > static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
> > > struct ftrace_regs *fregs)
> > > {
> > > - struct fprobe_hlist_node *node, *first;
> > > unsigned long *fgraph_data = NULL;
> > > unsigned long func = trace->func;
> > > + struct fprobe_hlist_node *node;
> > > + struct rhlist_head *head, *pos;
> > > unsigned long ret_ip;
> > > int reserved_words;
> > > struct fprobe *fp;
> > > @@ -260,14 +263,11 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
> > > if (WARN_ON_ONCE(!fregs))
> > > return 0;
> > >
> > > - first = node = find_first_fprobe_node(func);
> > > - if (unlikely(!first))
> > > - return 0;
> > > -
> > > + head = rhltable_lookup(&fprobe_ip_table, &func, fprobe_rht_params);
> >
> > ditto
>
> So this was pointed in the previous thread. In fprobe_entry(), the
> preempt is disabled already. Thus we don't need locking rcu.
>
> Thank you,
>
> >
> > jirka
> >
> >
> > > reserved_words = 0;
> > > - hlist_for_each_entry_from_rcu(node, hlist) {
> > > + rhl_for_each_entry_rcu(node, pos, head, hlist) {
> > > if (node->addr != func)
> > > - break;
> > > + continue;
> > > fp = READ_ONCE(node->fp);
> > > if (!fp || !fp->exit_handler)
> > > continue;
> > > @@ -278,13 +278,12 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
> > > reserved_words +=
> > > FPROBE_HEADER_SIZE_IN_LONG + SIZE_IN_LONG(fp->entry_data_size);
> > > }
> > > - node = first;
> > > if (reserved_words) {
> > > fgraph_data = fgraph_reserve_data(gops->idx, reserved_words * sizeof(long));
> > > if (unlikely(!fgraph_data)) {
> > > - hlist_for_each_entry_from_rcu(node, hlist) {
> > > + rhl_for_each_entry_rcu(node, pos, head, hlist) {
> > > if (node->addr != func)
> > > - break;
> > > + continue;
> > > fp = READ_ONCE(node->fp);
> > > if (fp && !fprobe_disabled(fp))
> > > fp->nmissed++;
> > > @@ -299,12 +298,12 @@ static int fprobe_entry(struct ftrace_graph_ent *trace, struct fgraph_ops *gops,
> > > */
> > > ret_ip = ftrace_regs_get_return_address(fregs);
> > > used = 0;
> > > - hlist_for_each_entry_from_rcu(node, hlist) {
> > > + rhl_for_each_entry_rcu(node, pos, head, hlist) {
> > > int data_size;
> > > void *data;
> > >
> > > if (node->addr != func)
> > > - break;
> > > + continue;
> > > fp = READ_ONCE(node->fp);
> > > if (!fp || fprobe_disabled(fp))
> > > continue;
> > > @@ -448,25 +447,21 @@ static int fprobe_addr_list_add(struct fprobe_addr_list *alist, unsigned long ad
> > > return 0;
> > > }
> > >
> > > -static void fprobe_remove_node_in_module(struct module *mod, struct hlist_head *head,
> > > - struct fprobe_addr_list *alist)
> > > +static void fprobe_remove_node_in_module(struct module *mod, struct fprobe_hlist_node *node,
> > > + struct fprobe_addr_list *alist)
> > > {
> > > - struct fprobe_hlist_node *node;
> > > int ret = 0;
> > >
> > > - hlist_for_each_entry_rcu(node, head, hlist,
> > > - lockdep_is_held(&fprobe_mutex)) {
> > > - if (!within_module(node->addr, mod))
> > > - continue;
> > > - if (delete_fprobe_node(node))
> > > - continue;
> > > - /*
> > > - * If failed to update alist, just continue to update hlist.
> > > - * Therefore, at list user handler will not hit anymore.
> > > - */
> > > - if (!ret)
> > > - ret = fprobe_addr_list_add(alist, node->addr);
> > > - }
> > > + if (!within_module(node->addr, mod))
> > > + return;
> > > + if (delete_fprobe_node(node))
> > > + return;
> > > + /*
> > > + * If failed to update alist, just continue to update hlist.
> > > + * Therefore, at list user handler will not hit anymore.
> > > + */
> > > + if (!ret)
> > > + ret = fprobe_addr_list_add(alist, node->addr);
> > > }
> > >
> > > /* Handle module unloading to manage fprobe_ip_table. */
> > > @@ -474,8 +469,9 @@ static int fprobe_module_callback(struct notifier_block *nb,
> > > unsigned long val, void *data)
> > > {
> > > struct fprobe_addr_list alist = {.size = FPROBE_IPS_BATCH_INIT};
> > > + struct fprobe_hlist_node *node;
> > > + struct rhashtable_iter iter;
> > > struct module *mod = data;
> > > - int i;
> > >
> > > if (val != MODULE_STATE_GOING)
> > > return NOTIFY_DONE;
> > > @@ -486,8 +482,16 @@ static int fprobe_module_callback(struct notifier_block *nb,
> > > return NOTIFY_DONE;
> > >
> > > mutex_lock(&fprobe_mutex);
> > > - for (i = 0; i < FPROBE_IP_TABLE_SIZE; i++)
> > > - fprobe_remove_node_in_module(mod, &fprobe_ip_table[i], &alist);
> > > + rhltable_walk_enter(&fprobe_ip_table, &iter);
> > > + do {
> > > + rhashtable_walk_start(&iter);
> > > +
> > > + while ((node = rhashtable_walk_next(&iter)) && !IS_ERR(node))
> > > + fprobe_remove_node_in_module(mod, node, &alist);
> > > +
> > > + rhashtable_walk_stop(&iter);
> > > + } while (node == ERR_PTR(-EAGAIN));
> > > + rhashtable_walk_exit(&iter);
> > >
> > > if (alist.index < alist.size && alist.index > 0)
> > > ftrace_set_filter_ips(&fprobe_graph_ops.ops,
> > > @@ -727,8 +731,16 @@ int register_fprobe_ips(struct fprobe *fp, unsigned long *addrs, int num)
> > > ret = fprobe_graph_add_ips(addrs, num);
> > > if (!ret) {
> > > add_fprobe_hash(fp);
> > > - for (i = 0; i < hlist_array->size; i++)
> > > - insert_fprobe_node(&hlist_array->array[i]);
> > > + for (i = 0; i < hlist_array->size; i++) {
> > > + ret = insert_fprobe_node(&hlist_array->array[i]);
> > > + if (ret)
> > > + break;
> > > + }
> > > + /* fallback on insert error */
> > > + if (ret) {
> > > + for (i--; i >= 0; i--)
> > > + delete_fprobe_node(&hlist_array->array[i]);
> > > + }
> > > }
> > > mutex_unlock(&fprobe_mutex);
> > >
> > > @@ -824,3 +836,10 @@ int unregister_fprobe(struct fprobe *fp)
> > > return ret;
> > > }
> > > EXPORT_SYMBOL_GPL(unregister_fprobe);
> > > +
> > > +static int __init fprobe_initcall(void)
> > > +{
> > > + rhltable_init(&fprobe_ip_table, &fprobe_rht_params);
> > > + return 0;
> > > +}
> > > +late_initcall(fprobe_initcall);
> > > --
> > > 2.50.1
> > >
> > >
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@...nel.org>
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