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Subject[PATCH][kprobe] enabling booster on the preemptible kernel
Hi Anil,
Could you give me your Ack for this patch?

From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

This patch enables the kprobe-booster on the preemptible kernel.
For this purpose, I introduced a kind of garbage collector of
the instruction slots. This garbage collector checks safety before
releasing the garbage slots.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

---

When we are unregistering a kprobe-booster, we can't release
its instruction buffer immediately on the preemptive kernel,
because some processes might be preempted on the buffer.
The freeze_processes() and thaw_processes() functions can
clean most of processes up from the buffer. There are still
some non-frozen threads who have the PF_NOFREEZE flag. If
those threads are sleeping (not preempted) at the known place
outside the buffer, we can ensure safety of freeing.

However, the processing of this check routine takes a long time.
So, this patch introduces the garbage collection mechanism of
insn_slot. It also introduces the "dirty" flag to free_insn_slot
because of efficiency.
The "clean" instruction slots (dirty flag is cleared) are
released immediately. But the "dirty" slots which are used
by boosted kprobes, are marked as garbages.
collect_garbage_slots() will be invoked to release "dirty"
slots if there are more than INSNS_PER_PAGE garbage slots
or if there are no unused slots.

arch/i386/kernel/kprobes.c | 4 -
arch/ia64/kernel/kprobes.c | 2
arch/powerpc/kernel/kprobes.c | 2
arch/s390/kernel/kprobes.c | 2
arch/x86_64/kernel/kprobes.c | 2
include/linux/kprobes.h | 2
kernel/kprobes.c | 117 ++++++++++++++++++++++++++++++++++--------
7 files changed, 103 insertions(+), 28 deletions(-)

Index: linux-2.6.19-rc5-mm2/kernel/kprobes.c
===================================================================
--- linux-2.6.19-rc5-mm2.orig/kernel/kprobes.c
+++ linux-2.6.19-rc5-mm2/kernel/kprobes.c
@@ -38,6 +38,7 @@
#include <linux/module.h>
#include <linux/moduleloader.h>
#include <linux/kallsyms.h>
+#include <linux/freezer.h>
#include <asm-generic/sections.h>
#include <asm/cacheflush.h>
#include <asm/errno.h>
@@ -83,9 +84,36 @@ struct kprobe_insn_page {
kprobe_opcode_t *insns; /* Page of instruction slots */
char slot_used[INSNS_PER_PAGE];
int nused;
+ int ngarbage;
};

static struct hlist_head kprobe_insn_pages;
+static int kprobe_garbage_slots;
+static int collect_garbage_slots(void);
+
+static int __kprobes check_safety(void)
+{
+ int ret = 0;
+#if defined(CONFIG_PREEMPT) && defined(CONFIG_PM)
+ ret = freeze_processes();
+ if (ret == 0) {
+ struct task_struct *p, *q;
+ do_each_thread(p, q) {
+ if (p != current && p->state == TASK_RUNNING &&
+ p->pid != 0) {
+ printk("Check failed: %s is running\n",p->comm);
+ ret = -1;
+ goto loop_end;
+ }
+ } while_each_thread(p, q);
+ }
+loop_end:
+ thaw_processes();
+#else
+ synchronize_sched();
+#endif
+ return ret;
+}

/**
* get_insn_slot() - Find a slot on an executable page for an instruction.
@@ -96,6 +124,7 @@ kprobe_opcode_t __kprobes *get_insn_slot
struct kprobe_insn_page *kip;
struct hlist_node *pos;

+ retry:
hlist_for_each(pos, &kprobe_insn_pages) {
kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
if (kip->nused < INSNS_PER_PAGE) {
@@ -112,7 +141,11 @@ kprobe_opcode_t __kprobes *get_insn_slot
}
}

- /* All out of space. Need to allocate a new page. Use slot 0.*/
+ /* If there are any garbage slots, collect it and try again. */
+ if (kprobe_garbage_slots && collect_garbage_slots() == 0) {
+ goto retry;
+ }
+ /* All out of space. Need to allocate a new page. Use slot 0. */
kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
if (!kip) {
return NULL;
@@ -133,10 +166,62 @@ kprobe_opcode_t __kprobes *get_insn_slot
memset(kip->slot_used, 0, INSNS_PER_PAGE);
kip->slot_used[0] = 1;
kip->nused = 1;
+ kip->ngarbage = 0;
return kip->insns;
}

-void __kprobes free_insn_slot(kprobe_opcode_t *slot)
+/* Return 1 if all garbages are collected, otherwise 0. */
+static int __kprobes collect_one_slot(struct kprobe_insn_page *kip, int idx)
+{
+ kip->slot_used[idx] = 0;
+ kip->nused--;
+ if (kip->nused == 0) {
+ /*
+ * Page is no longer in use. Free it unless
+ * it's the last one. We keep the last one
+ * so as not to have to set it up again the
+ * next time somebody inserts a probe.
+ */
+ hlist_del(&kip->hlist);
+ if (hlist_empty(&kprobe_insn_pages)) {
+ INIT_HLIST_NODE(&kip->hlist);
+ hlist_add_head(&kip->hlist,
+ &kprobe_insn_pages);
+ } else {
+ module_free(NULL, kip->insns);
+ kfree(kip);
+ }
+ return 1;
+ }
+ return 0;
+}
+
+static int __kprobes collect_garbage_slots(void)
+{
+ struct kprobe_insn_page *kip;
+ struct hlist_node *pos, *next;
+
+ /* Ensure no-one is preepmted on the garbages */
+ if (check_safety() != 0)
+ return -EAGAIN;
+
+ hlist_for_each_safe(pos, next, &kprobe_insn_pages) {
+ int i;
+ kip = hlist_entry(pos, struct kprobe_insn_page, hlist);
+ if (kip->ngarbage == 0)
+ continue;
+ kip->ngarbage = 0; /* we will collect all garbages */
+ for (i = 0; i < INSNS_PER_PAGE; i++) {
+ if (kip->slot_used[i] == -1 &&
+ collect_one_slot(kip, i))
+ break;
+ }
+ }
+ kprobe_garbage_slots = 0;
+ return 0;
+}
+
+void __kprobes free_insn_slot(kprobe_opcode_t * slot, int dirty)
{
struct kprobe_insn_page *kip;
struct hlist_node *pos;
@@ -146,28 +231,18 @@ void __kprobes free_insn_slot(kprobe_opc
if (kip->insns <= slot &&
slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
int i = (slot - kip->insns) / MAX_INSN_SIZE;
- kip->slot_used[i] = 0;
- kip->nused--;
- if (kip->nused == 0) {
- /*
- * Page is no longer in use. Free it unless
- * it's the last one. We keep the last one
- * so as not to have to set it up again the
- * next time somebody inserts a probe.
- */
- hlist_del(&kip->hlist);
- if (hlist_empty(&kprobe_insn_pages)) {
- INIT_HLIST_NODE(&kip->hlist);
- hlist_add_head(&kip->hlist,
- &kprobe_insn_pages);
- } else {
- module_free(NULL, kip->insns);
- kfree(kip);
- }
+ if (dirty) {
+ kip->slot_used[i] = -1;
+ kip->ngarbage++;
+ } else {
+ collect_one_slot(kip, i);
}
- return;
+ break;
}
}
+ if (dirty && (++kprobe_garbage_slots > INSNS_PER_PAGE)) {
+ collect_garbage_slots();
+ }
}
#endif

Index: linux-2.6.19-rc5-mm2/arch/i386/kernel/kprobes.c
===================================================================
--- linux-2.6.19-rc5-mm2.orig/arch/i386/kernel/kprobes.c
+++ linux-2.6.19-rc5-mm2/arch/i386/kernel/kprobes.c
@@ -184,7 +184,7 @@ void __kprobes arch_disarm_kprobe(struct
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
mutex_lock(&kprobe_mutex);
- free_insn_slot(p->ainsn.insn);
+ free_insn_slot(p->ainsn.insn, (p->ainsn.boostable == 1));
mutex_unlock(&kprobe_mutex);
}

@@ -333,7 +333,7 @@ static int __kprobes kprobe_handler(stru
return 1;

ss_probe:
-#ifndef CONFIG_PREEMPT
+#if !defined(CONFIG_PREEMPT) || defined(CONFIG_PM)
if (p->ainsn.boostable == 1 && !p->post_handler){
/* Boost up -- we can execute copied instructions directly */
reset_current_kprobe();
Index: linux-2.6.19-rc5-mm2/arch/ia64/kernel/kprobes.c
===================================================================
--- linux-2.6.19-rc5-mm2.orig/arch/ia64/kernel/kprobes.c
+++ linux-2.6.19-rc5-mm2/arch/ia64/kernel/kprobes.c
@@ -481,7 +481,7 @@ void __kprobes arch_disarm_kprobe(struct
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
mutex_lock(&kprobe_mutex);
- free_insn_slot(p->ainsn.insn);
+ free_insn_slot(p->ainsn.insn, 0);
mutex_unlock(&kprobe_mutex);
}
/*
Index: linux-2.6.19-rc5-mm2/arch/powerpc/kernel/kprobes.c
===================================================================
--- linux-2.6.19-rc5-mm2.orig/arch/powerpc/kernel/kprobes.c
+++ linux-2.6.19-rc5-mm2/arch/powerpc/kernel/kprobes.c
@@ -85,7 +85,7 @@ void __kprobes arch_disarm_kprobe(struct
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
mutex_lock(&kprobe_mutex);
- free_insn_slot(p->ainsn.insn);
+ free_insn_slot(p->ainsn.insn, 0);
mutex_unlock(&kprobe_mutex);
}

Index: linux-2.6.19-rc5-mm2/arch/s390/kernel/kprobes.c
===================================================================
--- linux-2.6.19-rc5-mm2.orig/arch/s390/kernel/kprobes.c
+++ linux-2.6.19-rc5-mm2/arch/s390/kernel/kprobes.c
@@ -200,7 +200,7 @@ void __kprobes arch_disarm_kprobe(struct
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
mutex_lock(&kprobe_mutex);
- free_insn_slot(p->ainsn.insn);
+ free_insn_slot(p->ainsn.insn, 0);
mutex_unlock(&kprobe_mutex);
}

Index: linux-2.6.19-rc5-mm2/arch/x86_64/kernel/kprobes.c
===================================================================
--- linux-2.6.19-rc5-mm2.orig/arch/x86_64/kernel/kprobes.c
+++ linux-2.6.19-rc5-mm2/arch/x86_64/kernel/kprobes.c
@@ -224,7 +224,7 @@ void __kprobes arch_disarm_kprobe(struct
void __kprobes arch_remove_kprobe(struct kprobe *p)
{
mutex_lock(&kprobe_mutex);
- free_insn_slot(p->ainsn.insn);
+ free_insn_slot(p->ainsn.insn, 0);
mutex_unlock(&kprobe_mutex);
}

Index: linux-2.6.19-rc5-mm2/include/linux/kprobes.h
===================================================================
--- linux-2.6.19-rc5-mm2.orig/include/linux/kprobes.h
+++ linux-2.6.19-rc5-mm2/include/linux/kprobes.h
@@ -165,7 +165,7 @@ extern void arch_disarm_kprobe(struct kp
extern int arch_init_kprobes(void);
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);
+extern void free_insn_slot(kprobe_opcode_t *slot, int dirty);
extern void kprobes_inc_nmissed_count(struct kprobe *p);

/* Get the kprobe at this addr (if any) - called with preemption disabled */

-
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