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kprobes: Replace rp->free_instance with freelist

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/159870623583.1229682.17472357584134058687.stgit@devnote2
This commit is contained in:
Peter Zijlstra 2020-08-29 22:03:56 +09:00 committed by Ingo Molnar
parent e563604a5f
commit 6e426e0fcd
2 changed files with 29 additions and 37 deletions
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8
include/linux/kprobes.h
View File

@ -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;

58
kernel/kprobes.c
View File

@ -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);
}
@ -1290,11 +1287,14 @@ 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);
__llist_add(&ri->llist, &current->kretprobe_instances);
} else {
fn = freelist_try_get(&rp->freelist);
if (!fn) {
rp->nmissed++;
raw_spin_unlock_irqrestore(&rp->lock, flags);
return 0;
}
ri = container_of(fn, struct kretprobe_instance, freelist);
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);
if (!rp->rph)
return -ENOMEM;
@ -2023,8 +2016,7 @@ 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);