[PATCH v4 23/23] kprobes: Replace rp->free_instance with freelist

Masami Hiramatsu
2020-08-28T12:31:22Z

From: Peter Zijlstra <peterz@infradead.org>

Gets rid of rp->lock, and as a result kretprobes are now fully
lockless.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
Changes
- [MH] expel the llist from anon union in kretprobe_instance
---
include/linux/kprobes.h | 8 +++----
kernel/kprobes.c | 56 ++++++++++++++++++++---------------------------
2 files changed, 28 insertions(+), 36 deletions(-)

diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index d7cdae2d8f2e..aa330bfefefd 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -28,6 +28,7 @@
#include <linux/mutex.h>
#include <linux/ftrace.h>
#include <linux/refcount.h>
+#include <linux/freelist.h>
#include <asm/kprobes.h>

#ifdef CONFIG_KPROBES
@@ -157,17 +158,16 @@ struct kretprobe {
int maxactive;
int nmissed;
size_t data_size;
- struct hlist_head free_instances;
+ struct freelist_head freelist;
struct kretprobe_holder *rph;
- raw_spinlock_t lock;
};

struct kretprobe_instance {
union {
- struct llist_node llist;
- struct hlist_node hlist;
+ struct freelist_node freelist;
struct rcu_head rcu;
};
+ struct llist_node llist;
struct kretprobe_holder *rph;
kprobe_opcode_t *ret_addr;
void *fp;
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 95390eb130f4..56cd865877fa 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1228,11 +1228,8 @@ static void recycle_rp_inst(struct kretprobe_instance *ri)
{
struct kretprobe *rp = get_kretprobe(ri);

- INIT_HLIST_NODE(&ri->hlist);
if (likely(rp)) {
- raw_spin_lock(&rp->lock);
- hlist_add_head(&ri->hlist, &rp->free_instances);
- raw_spin_unlock(&rp->lock);
+ freelist_add(&ri->freelist, &rp->freelist);
} else
call_rcu(&ri->rcu, free_rp_inst_rcu);
}
@@ -1292,11 +1289,14 @@ NOKPROBE_SYMBOL(kprobe_flush_task);
static inline void free_rp_inst(struct kretprobe *rp)
{
struct kretprobe_instance *ri;
- struct hlist_node *next;
+ struct freelist_node *node;
int count = 0;

- hlist_for_each_entry_safe(ri, next, &rp->free_instances, hlist) {
- hlist_del(&ri->hlist);
+ node = rp->freelist.head;
+ while (node) {
+ ri = container_of(node, struct kretprobe_instance, freelist);
+ node = node->next;
+
kfree(ri);
count++;
}
@@ -1925,32 +1925,26 @@ NOKPROBE_SYMBOL(__kretprobe_trampoline_handler)
static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
{
struct kretprobe *rp = container_of(p, struct kretprobe, kp);
- unsigned long flags = 0;
struct kretprobe_instance *ri;
+ struct freelist_node *fn;

- /* TODO: consider to only swap the RA after the last pre_handler fired */
- raw_spin_lock_irqsave(&rp->lock, flags);
- if (!hlist_empty(&rp->free_instances)) {
- ri = hlist_entry(rp->free_instances.first,
- struct kretprobe_instance, hlist);
- hlist_del(&ri->hlist);
- raw_spin_unlock_irqrestore(&rp->lock, flags);
-
- if (rp->entry_handler && rp->entry_handler(ri, regs)) {
- raw_spin_lock_irqsave(&rp->lock, flags);
- hlist_add_head(&ri->hlist, &rp->free_instances);
- raw_spin_unlock_irqrestore(&rp->lock, flags);
- return 0;
- }
-
- arch_prepare_kretprobe(ri, regs);
+ fn = freelist_try_get(&rp->freelist);
+ if (!fn) {
+ rp->nmissed++;
+ return 0;
+ }

- __llist_add(&ri->llist, &current->kretprobe_instances);
+ ri = container_of(fn, struct kretprobe_instance, freelist);

- } else {
- rp->nmissed++;
- raw_spin_unlock_irqrestore(&rp->lock, flags);
+ if (rp->entry_handler && rp->entry_handler(ri, regs)) {
+ freelist_add(&ri->freelist, &rp->freelist);
+ return 0;
}
+
+ arch_prepare_kretprobe(ri, regs);
+
+ __llist_add(&ri->llist, &current->kretprobe_instances);
+
return 0;
}
NOKPROBE_SYMBOL(pre_handler_kretprobe);
@@ -2007,8 +2001,7 @@ int register_kretprobe(struct kretprobe *rp)
rp->maxactive = num_possible_cpus();
#endif
}
- raw_spin_lock_init(&rp->lock);
- INIT_HLIST_HEAD(&rp->free_instances);
+ rp->freelist.head = NULL;
rp->rph = kzalloc(sizeof(struct kretprobe_holder), GFP_KERNEL);
rp->rph->rp = rp;
for (i = 0; i < rp->maxactive; i++) {
@@ -2020,8 +2013,7 @@ int register_kretprobe(struct kretprobe *rp)
return -ENOMEM;
}
inst->rph = rp->rph;
- INIT_HLIST_NODE(&inst->hlist);
- hlist_add_head(&inst->hlist, &rp->free_instances);
+ freelist_add(&inst->freelist, &rp->freelist);
}
refcount_set(&rp->rph->ref, i);