Commit 3516a460 authored by Ananth N Mavinakayanahalli's avatar Ananth N Mavinakayanahalli Committed by Linus Torvalds
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[PATCH] Kprobes: Use RCU for (un)register synchronization - base changes



Changes to the base kprobes infrastructure to use RCU for synchronization
during kprobe registration and unregistration.  These changes coupled with the
arch kprobe changes (next in series):

a. serialize registration and unregistration of kprobes.
b. enable lockless execution of handlers. Handlers can now run in parallel.
Signed-off-by: default avatarAnanth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: default avatarAnil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e7a510f9
......@@ -34,6 +34,8 @@
#include <linux/notifier.h>
#include <linux/smp.h>
#include <linux/percpu.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <asm/kprobes.h>
......@@ -146,10 +148,7 @@ struct kretprobe_instance {
};
#ifdef CONFIG_KPROBES
/* Locks kprobe: irq must be disabled */
void lock_kprobes(void);
void unlock_kprobes(void);
extern spinlock_t kretprobe_lock;
extern int arch_prepare_kprobe(struct kprobe *p);
extern void arch_copy_kprobe(struct kprobe *p);
extern void arch_arm_kprobe(struct kprobe *p);
......@@ -160,7 +159,7 @@ extern void show_registers(struct pt_regs *regs);
extern kprobe_opcode_t *get_insn_slot(void);
extern void free_insn_slot(kprobe_opcode_t *slot);
/* Get the kprobe at this addr (if any). Must have called lock_kprobes */
/* Get the kprobe at this addr (if any) - called under a rcu_read_lock() */
struct kprobe *get_kprobe(void *addr);
struct hlist_head * kretprobe_inst_table_head(struct task_struct *tsk);
......
......@@ -32,7 +32,6 @@
* <prasanna@in.ibm.com> added function-return probes.
*/
#include <linux/kprobes.h>
#include <linux/spinlock.h>
#include <linux/hash.h>
#include <linux/init.h>
#include <linux/slab.h>
......@@ -49,8 +48,8 @@
static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
unsigned int kprobe_cpu = NR_CPUS;
static DEFINE_SPINLOCK(kprobe_lock);
static DEFINE_SPINLOCK(kprobe_lock); /* Protects kprobe_table */
DEFINE_SPINLOCK(kretprobe_lock); /* Protects kretprobe_inst_table */
static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
/*
......@@ -153,41 +152,6 @@ void __kprobes free_insn_slot(kprobe_opcode_t *slot)
}
}
/* Locks kprobe: irqs must be disabled */
void __kprobes lock_kprobes(void)
{
unsigned long flags = 0;
/* Avoiding local interrupts to happen right after we take the kprobe_lock
* and before we get a chance to update kprobe_cpu, this to prevent
* deadlock when we have a kprobe on ISR routine and a kprobe on task
* routine
*/
local_irq_save(flags);
spin_lock(&kprobe_lock);
kprobe_cpu = smp_processor_id();
local_irq_restore(flags);
}
void __kprobes unlock_kprobes(void)
{
unsigned long flags = 0;
/* Avoiding local interrupts to happen right after we update
* kprobe_cpu and before we get a a chance to release kprobe_lock,
* this to prevent deadlock when we have a kprobe on ISR routine and
* a kprobe on task routine
*/
local_irq_save(flags);
kprobe_cpu = NR_CPUS;
spin_unlock(&kprobe_lock);
local_irq_restore(flags);
}
/* We have preemption disabled.. so it is safe to use __ versions */
static inline void set_kprobe_instance(struct kprobe *kp)
{
......@@ -199,15 +163,20 @@ static inline void reset_kprobe_instance(void)
__get_cpu_var(kprobe_instance) = NULL;
}
/* You have to be holding the kprobe_lock */
/*
* This routine is called either:
* - under the kprobe_lock spinlock - during kprobe_[un]register()
* OR
* - under an rcu_read_lock() - from arch/xxx/kernel/kprobes.c
*/
struct kprobe __kprobes *get_kprobe(void *addr)
{
struct hlist_head *head;
struct hlist_node *node;
struct kprobe *p;
head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];
hlist_for_each(node, head) {
struct kprobe *p = hlist_entry(node, struct kprobe, hlist);
hlist_for_each_entry_rcu(p, node, head, hlist) {
if (p->addr == addr)
return p;
}
......@@ -222,7 +191,7 @@ static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)
{
struct kprobe *kp;
list_for_each_entry(kp, &p->list, list) {
list_for_each_entry_rcu(kp, &p->list, list) {
if (kp->pre_handler) {
set_kprobe_instance(kp);
if (kp->pre_handler(kp, regs))
......@@ -238,7 +207,7 @@ static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
{
struct kprobe *kp;
list_for_each_entry(kp, &p->list, list) {
list_for_each_entry_rcu(kp, &p->list, list) {
if (kp->post_handler) {
set_kprobe_instance(kp);
kp->post_handler(kp, regs, flags);
......@@ -277,6 +246,7 @@ static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)
return ret;
}
/* Called with kretprobe_lock held */
struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
{
struct hlist_node *node;
......@@ -286,6 +256,7 @@ struct kretprobe_instance __kprobes *get_free_rp_inst(struct kretprobe *rp)
return NULL;
}
/* Called with kretprobe_lock held */
static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
*rp)
{
......@@ -296,6 +267,7 @@ static struct kretprobe_instance __kprobes *get_used_rp_inst(struct kretprobe
return NULL;
}
/* Called with kretprobe_lock held */
void __kprobes add_rp_inst(struct kretprobe_instance *ri)
{
/*
......@@ -314,6 +286,7 @@ void __kprobes add_rp_inst(struct kretprobe_instance *ri)
hlist_add_head(&ri->uflist, &ri->rp->used_instances);
}
/* Called with kretprobe_lock held */
void __kprobes recycle_rp_inst(struct kretprobe_instance *ri)
{
/* remove rp inst off the rprobe_inst_table */
......@@ -347,13 +320,13 @@ void __kprobes kprobe_flush_task(struct task_struct *tk)
struct hlist_node *node, *tmp;
unsigned long flags = 0;
spin_lock_irqsave(&kprobe_lock, flags);
spin_lock_irqsave(&kretprobe_lock, flags);
head = kretprobe_inst_table_head(current);
hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
if (ri->task == tk)
recycle_rp_inst(ri);
}
spin_unlock_irqrestore(&kprobe_lock, flags);
spin_unlock_irqrestore(&kretprobe_lock, flags);
}
/*
......@@ -364,9 +337,12 @@ static int __kprobes pre_handler_kretprobe(struct kprobe *p,
struct pt_regs *regs)
{
struct kretprobe *rp = container_of(p, struct kretprobe, kp);
unsigned long flags = 0;
/*TODO: consider to only swap the RA after the last pre_handler fired */
spin_lock_irqsave(&kretprobe_lock, flags);
arch_prepare_kretprobe(rp, regs);
spin_unlock_irqrestore(&kretprobe_lock, flags);
return 0;
}
......@@ -397,13 +373,13 @@ static int __kprobes add_new_kprobe(struct kprobe *old_p, struct kprobe *p)
struct kprobe *kp;
if (p->break_handler) {
list_for_each_entry(kp, &old_p->list, list) {
list_for_each_entry_rcu(kp, &old_p->list, list) {
if (kp->break_handler)
return -EEXIST;
}
list_add_tail(&p->list, &old_p->list);
list_add_tail_rcu(&p->list, &old_p->list);
} else
list_add(&p->list, &old_p->list);
list_add_rcu(&p->list, &old_p->list);
return 0;
}
......@@ -421,18 +397,18 @@ static inline void add_aggr_kprobe(struct kprobe *ap, struct kprobe *p)
ap->break_handler = aggr_break_handler;
INIT_LIST_HEAD(&ap->list);
list_add(&p->list, &ap->list);
list_add_rcu(&p->list, &ap->list);
INIT_HLIST_NODE(&ap->hlist);
hlist_del(&p->hlist);
hlist_add_head(&ap->hlist,
hlist_del_rcu(&p->hlist);
hlist_add_head_rcu(&ap->hlist,
&kprobe_table[hash_ptr(ap->addr, KPROBE_HASH_BITS)]);
}
/*
* This is the second or subsequent kprobe at the address - handle
* the intricacies
* TODO: Move kcalloc outside the spinlock
* TODO: Move kcalloc outside the spin_lock
*/
static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
struct kprobe *p)
......@@ -458,7 +434,7 @@ static int __kprobes register_aggr_kprobe(struct kprobe *old_p,
static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
{
arch_disarm_kprobe(p);
hlist_del(&p->hlist);
hlist_del_rcu(&p->hlist);
spin_unlock_irqrestore(&kprobe_lock, flags);
arch_remove_kprobe(p);
}
......@@ -466,11 +442,10 @@ static inline void cleanup_kprobe(struct kprobe *p, unsigned long flags)
static inline void cleanup_aggr_kprobe(struct kprobe *old_p,
struct kprobe *p, unsigned long flags)
{
list_del(&p->list);
if (list_empty(&old_p->list)) {
list_del_rcu(&p->list);
if (list_empty(&old_p->list))
cleanup_kprobe(old_p, flags);
kfree(old_p);
} else
else
spin_unlock_irqrestore(&kprobe_lock, flags);
}
......@@ -493,9 +468,9 @@ int __kprobes register_kprobe(struct kprobe *p)
if ((ret = arch_prepare_kprobe(p)) != 0)
goto rm_kprobe;
p->nmissed = 0;
spin_lock_irqsave(&kprobe_lock, flags);
old_p = get_kprobe(p->addr);
p->nmissed = 0;
if (old_p) {
ret = register_aggr_kprobe(old_p, p);
goto out;
......@@ -503,7 +478,7 @@ int __kprobes register_kprobe(struct kprobe *p)
arch_copy_kprobe(p);
INIT_HLIST_NODE(&p->hlist);
hlist_add_head(&p->hlist,
hlist_add_head_rcu(&p->hlist,
&kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
arch_arm_kprobe(p);
......@@ -524,10 +499,16 @@ void __kprobes unregister_kprobe(struct kprobe *p)
spin_lock_irqsave(&kprobe_lock, flags);
old_p = get_kprobe(p->addr);
if (old_p) {
/* cleanup_*_kprobe() does the spin_unlock_irqrestore */
if (old_p->pre_handler == aggr_pre_handler)
cleanup_aggr_kprobe(old_p, p, flags);
else
cleanup_kprobe(p, flags);
synchronize_sched();
if (old_p->pre_handler == aggr_pre_handler &&
list_empty(&old_p->list))
kfree(old_p);
} else
spin_unlock_irqrestore(&kprobe_lock, flags);
}
......@@ -604,13 +585,13 @@ void __kprobes unregister_kretprobe(struct kretprobe *rp)
unregister_kprobe(&rp->kp);
/* No race here */
spin_lock_irqsave(&kprobe_lock, flags);
spin_lock_irqsave(&kretprobe_lock, flags);
free_rp_inst(rp);
while ((ri = get_used_rp_inst(rp)) != NULL) {
ri->rp = NULL;
hlist_del(&ri->uflist);
}
spin_unlock_irqrestore(&kprobe_lock, flags);
spin_unlock_irqrestore(&kretprobe_lock, flags);
}
static int __init init_kprobes(void)
......
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