Re: [RFC] [PATCH] To improve kretprobe scalability

From: Srinivasa D S
Date: Thu May 22 2008 - 09:59:17 EST

On Thursday 22 May 2008 05:02:35 am Andrew Morton wrote:
> On Wed, 21 May 2008 06:32:17 +0530
>
> Srinivasa D S <srinivasa@xxxxxxxxxx> wrote:
> > Currently list of kretprobe instances are stored in kretprobe object (as
> > used_instances,free_instances) and in kretprobe hash table.
>
> Are you sure that all the code which was previously globally serialised
> is safe to run concurrently?

Yes, Iam sure. I have tested this patch on all architecture. I have written
the systemtap script which probes all systemcalls and its return values. This
works fine on patched kernel.

>
> > Time duration for kernel compilation ("make -j 8") on a 8-way ppc64
> > system with return probes set on all systemcalls looks like this.
> >
> > Patched-kernel Un-Patched kernel
> > ============================================================
> > real 10m49.694s real 13m21.276s
> > user 35m6.117s user 40m30.454s
> > sys 2m55.480s sys 3m23.221s
> > ===========================================================
>
> That's a large speedup.
>
> Do you have available the figures for the same workload when no probes
> are set at all?

As I was concerned with the performance of kretprobes, I don't have figures on
the workload when probes are set. But, currently I have implemented your
cacheline aligned approach and captured this data. Please see below(in the
patch).

>
> > --- linux-2.6.26-rc2-mm1.orig/kernel/kprobes.c
> > +++ linux-2.6.26-rc2-mm1/kernel/kprobes.c
> >
> > DEFINE_MUTEX(kprobe_mutex); /* Protects kprobe_table */
> > -DEFINE_SPINLOCK(kretprobe_lock); /* Protects kretprobe_inst_table */
> > static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
> > +static spinlock_t kretprobe_table_locks[KPROBE_TABLE_SIZE];
>
> An array of 64 spinlocks. These will all be crammed into two or four
> cachelines. If there is really any concurrency in here, the contention
> will be large.
>
> I suggest that you experiment with one-lock-per-cacheline here and see
> whether it is worth doing that permanently.
>
> Something along the lines of
>
> static struct {
> spinlock_t lock __cacheline_aligned;
> } kretprobe_locks[KPROBE_TABLE_SIZE];
>
> static spinlock_t *kretprobe_lock_ptr(...)
> {
> return kretprobe_locks + hash(...);
> }
>
>

Thanks for the suggestion. I have implemented this approach and by looking at
the statistics(attached in the patch), there is slight improvement in
kretprobe performance.


> Also, none of this new code is needed on uniprocessor builds. Did we
> just add some bloat?
>

No Andrew, We just replaced old kretprobe_lock code with the new one. Since
kretprobe_lock was also used in arch dependent code, we have modified arch
dependent kprobes.c file.
But code added to kernel.[ch] is very less, 51 lines of code gets added to
kprobes.c(with the new patch, attached below) and this has caused speedup in
performance.

> > +void put_kretprobe_hash_lock(struct task_struct *tsk, unsigned long
> > *flags) {
> > - return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
> > + unsigned long hash = hash_ptr(tsk, KPROBE_HASH_BITS);
> > + spinlock_t *hlist_lock;
> > +
> > + hlist_lock = &kretprobe_table_locks[hash];
> > + spin_unlock_irqrestore(hlist_lock, *flags);
> > }
>
> I think these functions are misnamed. Generally functions whose names
> are of the form get_foo() and put_foo() are used for acquiring and
> releasing reference counts. These functions don't do that.
>
> kretprobe_hash_lock() and kretprobe_hash_unlock() would be better?

Sounds good to me, Done.

>
> > /*
> > @@ -401,17 +417,21 @@ void __kprobes kprobe_flush_task(struct
> > struct kretprobe_instance *ri;
> > struct hlist_head *head, empty_rp;
> > struct hlist_node *node, *tmp;
> > }
> > - spin_unlock_irqrestore(&kretprobe_lock, flags);
> > -
> > + spin_unlock_irqrestore(&kretprobe_table_locks[hash], flags);
>
> and of put_kretprobe_hash_lock(). Perhaps a separate function which
> just obtains the spinlock_t* is needed.

Added to the code.
>
> > + INIT_HLIST_HEAD(&empty_rp);
> > hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
> > hlist_del(&ri->hlist);

Resending the patch, Again


Currently list of kretprobe instances are stored in kretprobe object (as
used_instances,free_instances) and in kretprobe hash table. We have one
global kretprobe lock to serialise the access to these lists. This causes
only one kretprobe handler to execute at a time. Hence affects system
performance, particularly on SMP systems and when return probe is set on
lot of functions (like on all systemcalls).

Solution proposed here gives fine-grain locks that performs better on SMP
system compared to present kretprobe implementation.

Solution:
1) Instead of having one global lock to protect kretprobe instances
present
in kretprobe object and kretprobe hash table. We will have two locks, one lock
for protecting kretprobe hash table and another lock for kretporbe object.

2) We hold lock present in kretprobe object while we modify kretprobe
instance in
kretprobe object and we hold per-hash-list lock while modifying kretprobe
instances
present in that hash list. To prevent deadlock, we never grab a per-hash-list
lock while holding a kretprobe lock.

3) We can remove used_instances from struct kretprobe, as we can track used
instances of kretprobe instances using kretprobe hash table.

Time duration for kernel compilation ("make -j 8") on a 8-way ppc64 system
with return probes set on all systemcalls looks like this.

cacheline non-cacheline Un-patched kernel
aligned patch aligned patch
===============================================================================
real 9m46.784s 9m54.412s 10m2.450s
user 40m5.715s 40m7.142s 40m4.273s
sys 2m57.754s 2m58.583s 3m17.430s
===========================================================

Time duration for kernel compilation ("make -j 8) on the same system, when
kernel is not probed.
=========================
real 9m26.389s
user 40m8.775s
sys 2m7.283s
=========================

Please let me know your comments on the patch attached here.

Signed-off-by: Srinivasa DS <srinivasa@xxxxxxxxxx>
Signed-off-by: Jim Keniston <jkenisto@xxxxxxxxxx>



---
arch/arm/kernel/kprobes.c | 6 -
arch/ia64/kernel/kprobes.c | 6 -
arch/powerpc/kernel/kprobes.c | 6 -
arch/s390/kernel/kprobes.c | 6 -
arch/sparc64/kernel/kprobes.c | 11 +--
arch/x86/kernel/kprobes.c | 6 -
include/linux/kprobes.h | 7 +-
kernel/kprobes.c | 127
+++++++++++++++++++++++++++++-------------
8 files changed, 108 insertions(+), 67 deletions(-)

Index: linux-2.6.26-rc2-mm1/arch/ia64/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/arch/ia64/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/arch/ia64/kernel/kprobes.c
@@ -429,8 +429,7 @@ int __kprobes trampoline_probe_handler(s
((struct fnptr *)kretprobe_trampoline)->ip;

INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(current);
+ kretprobe_hash_lock(current, &head, &flags);

/*
* It is possible to have multiple instances associated with a given
@@ -485,7 +484,7 @@ int __kprobes trampoline_probe_handler(s
kretprobe_assert(ri, orig_ret_address, trampoline_address);

reset_current_kprobe();
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ kretprobe_hash_unlock(current, &flags);
preempt_enable_no_resched();

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
@@ -500,7 +499,6 @@ int __kprobes trampoline_probe_handler(s
return 1;
}

-/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
Index: linux-2.6.26-rc2-mm1/arch/powerpc/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/arch/powerpc/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/arch/powerpc/kernel/kprobes.c
@@ -127,7 +127,6 @@ static void __kprobes set_current_kprobe
kcb->kprobe_saved_msr = regs->msr;
}

-/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
@@ -294,8 +293,7 @@ static int __kprobes trampoline_probe_ha
unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;

INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(current);
+ kretprobe_hash_lock(current, &head, &flags);

/*
* It is possible to have multiple instances associated with a given
@@ -334,7 +332,7 @@ static int __kprobes trampoline_probe_ha
regs->nip = orig_ret_address;

reset_current_kprobe();
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ kretprobe_hash_unlock(current, &flags);
preempt_enable_no_resched();

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
Index: linux-2.6.26-rc2-mm1/arch/s390/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/arch/s390/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/arch/s390/kernel/kprobes.c
@@ -272,7 +272,6 @@ static void __kprobes set_current_kprobe
__ctl_store(kcb->kprobe_saved_ctl, 9, 11);
}

-/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
@@ -379,8 +378,7 @@ static int __kprobes trampoline_probe_ha
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;

INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(current);
+ kretprobe_hash_lock(current, &head, &flags);

/*
* It is possible to have multiple instances associated with a given
@@ -419,7 +417,7 @@ static int __kprobes trampoline_probe_ha
regs->psw.addr = orig_ret_address | PSW_ADDR_AMODE;

reset_current_kprobe();
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ kretprobe_hash_unlock(current, &flags);
preempt_enable_no_resched();

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
Index: linux-2.6.26-rc2-mm1/arch/x86/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/arch/x86/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/arch/x86/kernel/kprobes.c
@@ -431,7 +431,6 @@ static void __kprobes prepare_singlestep
regs->ip = (unsigned long)p->ainsn.insn;
}

-/* Called with kretprobe_lock held */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{
@@ -682,8 +681,7 @@ static __used __kprobes void *trampoline
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;

INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(current);
+ kretprobe_hash_lock(current, &head, &flags);
/* fixup registers */
#ifdef CONFIG_X86_64
regs->cs = __KERNEL_CS;
@@ -732,7 +730,7 @@ static __used __kprobes void *trampoline

kretprobe_assert(ri, orig_ret_address, trampoline_address);

- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ kretprobe_hash_unlock(current, &flags);

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
Index: linux-2.6.26-rc2-mm1/include/linux/kprobes.h
===================================================================
--- linux-2.6.26-rc2-mm1.orig/include/linux/kprobes.h
+++ linux-2.6.26-rc2-mm1/include/linux/kprobes.h
@@ -157,11 +157,10 @@ struct kretprobe {
int nmissed;
size_t data_size;
struct hlist_head free_instances;
- struct hlist_head used_instances;
+ spinlock_t lock;
};

struct kretprobe_instance {
- struct hlist_node uflist; /* either on free list or used list */
struct hlist_node hlist;
struct kretprobe *rp;
kprobe_opcode_t *ret_addr;
@@ -201,7 +200,6 @@ static inline int init_test_probes(void)
}
#endif /* CONFIG_KPROBES_SANITY_TEST */

-extern spinlock_t kretprobe_lock;
extern struct mutex kprobe_mutex;
extern int arch_prepare_kprobe(struct kprobe *p);
extern void arch_arm_kprobe(struct kprobe *p);
@@ -214,6 +212,9 @@ extern void kprobes_inc_nmissed_count(st

/* Get the kprobe at this addr (if any) - called with preemption disabled */
struct kprobe *get_kprobe(void *addr);
+void kretprobe_hash_lock(struct task_struct *tsk,
+ struct hlist_head **head, unsigned long *flags);
+void kretprobe_hash_unlock(struct task_struct *tsk, unsigned long *flags);
struct hlist_head * kretprobe_inst_table_head(struct task_struct *tsk);

/* kprobe_running() will just return the current_kprobe on this CPU */
Index: linux-2.6.26-rc2-mm1/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/kernel/kprobes.c
@@ -62,6 +62,7 @@
addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
#endif

+static int kprobes_initialized;
static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];

@@ -69,8 +70,15 @@ static struct hlist_head kretprobe_inst_
static bool kprobe_enabled;

DEFINE_MUTEX(kprobe_mutex); /* Protects kprobe_table */
-DEFINE_SPINLOCK(kretprobe_lock); /* Protects kretprobe_inst_table */
static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;
+static struct {
+ spinlock_t lock ____cacheline_aligned;
+} kretprobe_table_locks[KPROBE_TABLE_SIZE];
+
+static spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
+{
+ return &(kretprobe_table_locks[hash].lock);
+}

/*
* Normally, functions that we'd want to prohibit kprobes in, are marked
@@ -368,26 +376,53 @@ void __kprobes kprobes_inc_nmissed_count
return;
}

-/* Called with kretprobe_lock held */
void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
struct hlist_head *head)
{
+ struct kretprobe *rp = ri->rp;
+
/* remove rp inst off the rprobe_inst_table */
hlist_del(&ri->hlist);
- if (ri->rp) {
- /* remove rp inst off the used list */
- hlist_del(&ri->uflist);
- /* put rp inst back onto the free list */
- INIT_HLIST_NODE(&ri->uflist);
- hlist_add_head(&ri->uflist, &ri->rp->free_instances);
+ INIT_HLIST_NODE(&ri->hlist);
+ if (likely(rp)) {
+ spin_lock(&rp->lock);
+ hlist_add_head(&ri->hlist, &rp->free_instances);
+ spin_unlock(&rp->lock);
} else
/* Unregistering */
hlist_add_head(&ri->hlist, head);
}

-struct hlist_head __kprobes *kretprobe_inst_table_head(struct task_struct
*tsk)
+void kretprobe_hash_lock(struct task_struct *tsk,
+ struct hlist_head **head, unsigned long *flags)
+{
+ unsigned long hash = hash_ptr(tsk, KPROBE_HASH_BITS);
+ spinlock_t *hlist_lock;
+
+ *head = &kretprobe_inst_table[hash];
+ hlist_lock = kretprobe_table_lock_ptr(hash);
+ spin_lock_irqsave(hlist_lock, *flags);
+}
+
+void kretprobe_table_lock(unsigned long hash, unsigned long *flags)
{
- return &kretprobe_inst_table[hash_ptr(tsk, KPROBE_HASH_BITS)];
+ spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
+ spin_lock_irqsave(hlist_lock, *flags);
+}
+
+void kretprobe_hash_unlock(struct task_struct *tsk, unsigned long *flags)
+{
+ unsigned long hash = hash_ptr(tsk, KPROBE_HASH_BITS);
+ spinlock_t *hlist_lock;
+
+ hlist_lock = kretprobe_table_lock_ptr(hash);
+ spin_unlock_irqrestore(hlist_lock, *flags);
+}
+
+void kretprobe_table_unlock(unsigned long hash, unsigned long *flags)
+{
+ spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
+ spin_unlock_irqrestore(hlist_lock, *flags);
}

/*
@@ -401,17 +436,21 @@ void __kprobes kprobe_flush_task(struct
struct kretprobe_instance *ri;
struct hlist_head *head, empty_rp;
struct hlist_node *node, *tmp;
- unsigned long flags = 0;
+ unsigned long hash, flags = 0;

- INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(tk);
+ if (unlikely(!kprobes_initialized))
+ /* Early boot. kretprobe_table_locks not yet initialized. */
+ return;
+
+ hash = hash_ptr(tk, KPROBE_HASH_BITS);
+ head = &kretprobe_inst_table[hash];
+ kretprobe_table_lock(hash, &flags);
hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
if (ri->task == tk)
recycle_rp_inst(ri, &empty_rp);
}
- spin_unlock_irqrestore(&kretprobe_lock, flags);
-
+ kretprobe_table_unlock(hash, &flags);
+ INIT_HLIST_HEAD(&empty_rp);
hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
kfree(ri);
@@ -423,24 +462,29 @@ static inline void free_rp_inst(struct k
struct kretprobe_instance *ri;
struct hlist_node *pos, *next;

- hlist_for_each_entry_safe(ri, pos, next, &rp->free_instances, uflist) {
- hlist_del(&ri->uflist);
+ hlist_for_each_entry_safe(ri, pos, next, &rp->free_instances, hlist) {
+ hlist_del(&ri->hlist);
kfree(ri);
}
}

static void __kprobes cleanup_rp_inst(struct kretprobe *rp)
{
- unsigned long flags;
+ unsigned long flags, hash;
struct kretprobe_instance *ri;
struct hlist_node *pos, *next;
+ struct hlist_head *head;
+
/* No race here */
- spin_lock_irqsave(&kretprobe_lock, flags);
- hlist_for_each_entry_safe(ri, pos, next, &rp->used_instances, uflist) {
- ri->rp = NULL;
- hlist_del(&ri->uflist);
+ for (hash = 0; hash < KPROBE_TABLE_SIZE; hash++) {
+ kretprobe_table_lock(hash, &flags);
+ head = &kretprobe_inst_table[hash];
+ hlist_for_each_entry_safe(ri, pos, next, head, hlist) {
+ if (ri->rp == rp)
+ ri->rp = NULL;
+ }
+ kretprobe_table_unlock(hash, &flags);
}
- spin_unlock_irqrestore(&kretprobe_lock, flags);
free_rp_inst(rp);
}

@@ -829,32 +873,37 @@ static int __kprobes pre_handler_kretpro
struct pt_regs *regs)
{
struct kretprobe *rp = container_of(p, struct kretprobe, kp);
- unsigned long flags = 0;
+ unsigned long hash, flags = 0;
+ struct kretprobe_instance *ri;

/*TODO: consider to only swap the RA after the last pre_handler fired */
- spin_lock_irqsave(&kretprobe_lock, flags);
+ hash = hash_ptr(current, KPROBE_HASH_BITS);
+ spin_lock_irqsave(&rp->lock, flags);
if (!hlist_empty(&rp->free_instances)) {
- struct kretprobe_instance *ri;
-
ri = hlist_entry(rp->free_instances.first,
- struct kretprobe_instance, uflist);
+ struct kretprobe_instance, hlist);
+ hlist_del(&ri->hlist);
+ spin_unlock_irqrestore(&rp->lock, flags);
+
ri->rp = rp;
ri->task = current;

if (rp->entry_handler && rp->entry_handler(ri, regs)) {
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ spin_unlock_irqrestore(&rp->lock, flags);
return 0;
}

arch_prepare_kretprobe(ri, regs);

/* XXX(hch): why is there no hlist_move_head? */
- hlist_del(&ri->uflist);
- hlist_add_head(&ri->uflist, &ri->rp->used_instances);
- hlist_add_head(&ri->hlist, kretprobe_inst_table_head(ri->task));
- } else
+ INIT_HLIST_NODE(&ri->hlist);
+ kretprobe_table_lock(hash, &flags);
+ hlist_add_head(&ri->hlist, &kretprobe_inst_table[hash]);
+ kretprobe_table_unlock(hash, &flags);
+ } else {
rp->nmissed++;
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ spin_unlock_irqrestore(&rp->lock, flags);
+ }
return 0;
}

@@ -890,7 +939,7 @@ static int __kprobes __register_kretprob
rp->maxactive = NR_CPUS;
#endif
}
- INIT_HLIST_HEAD(&rp->used_instances);
+ spin_lock_init(&rp->lock);
INIT_HLIST_HEAD(&rp->free_instances);
for (i = 0; i < rp->maxactive; i++) {
inst = kmalloc(sizeof(struct kretprobe_instance) +
@@ -899,8 +948,8 @@ static int __kprobes __register_kretprob
free_rp_inst(rp);
return -ENOMEM;
}
- INIT_HLIST_NODE(&inst->uflist);
- hlist_add_head(&inst->uflist, &rp->free_instances);
+ INIT_HLIST_NODE(&inst->hlist);
+ hlist_add_head(&inst->hlist, &rp->free_instances);
}

rp->nmissed = 0;
@@ -1006,6 +1055,7 @@ static int __init init_kprobes(void)
for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
INIT_HLIST_HEAD(&kprobe_table[i]);
INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
+ spin_lock_init(&(kretprobe_table_locks[i].lock));
}

/*
@@ -1047,6 +1097,7 @@ static int __init init_kprobes(void)
err = arch_init_kprobes();
if (!err)
err = register_die_notifier(&kprobe_exceptions_nb);
+ kprobes_initialized = (err == 0);

if (!err)
init_test_probes();
Index: linux-2.6.26-rc2-mm1/arch/sparc64/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/arch/sparc64/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/arch/sparc64/kernel/kprobes.c
@@ -478,9 +478,9 @@ int __kprobes longjmp_break_handler(stru
return 0;
}

-/* Called with kretprobe_lock held. The value stored in the return
- * address register is actually 2 instructions before where the
- * callee will return to. Sequences usually look something like this
+/* The value stored in the return address register is actually 2
+ * instructions before where the callee will return to.
+ * Sequences usually look something like this
*
* call some_function <--- return register points here
* nop <--- call delay slot
@@ -512,8 +512,7 @@ int __kprobes trampoline_probe_handler(s
unsigned long trampoline_address =(unsigned long)&kretprobe_trampoline;

INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(current);
+ kretprobe_hash_lock(current, &head, &flags);

/*
* It is possible to have multiple instances associated with a given
@@ -553,7 +552,7 @@ int __kprobes trampoline_probe_handler(s
regs->tnpc = orig_ret_address + 4;

reset_current_kprobe();
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ kretprobe_hash_unlock(current, &flags);
preempt_enable_no_resched();

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
Index: linux-2.6.26-rc2-mm1/arch/arm/kernel/kprobes.c
===================================================================
--- linux-2.6.26-rc2-mm1.orig/arch/arm/kernel/kprobes.c
+++ linux-2.6.26-rc2-mm1/arch/arm/kernel/kprobes.c
@@ -296,8 +296,7 @@ static __used __kprobes void *trampoline
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;

INIT_HLIST_HEAD(&empty_rp);
- spin_lock_irqsave(&kretprobe_lock, flags);
- head = kretprobe_inst_table_head(current);
+ kretprobe_hash_lock(current, &head, &flags);

/*
* It is possible to have multiple instances associated with a given
@@ -337,7 +336,7 @@ static __used __kprobes void *trampoline
}

kretprobe_assert(ri, orig_ret_address, trampoline_address);
- spin_unlock_irqrestore(&kretprobe_lock, flags);
+ kretprobe_hash_unlock(current, &flags);

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
hlist_del(&ri->hlist);
@@ -347,7 +346,6 @@ static __used __kprobes void *trampoline
return (void *)orig_ret_address;
}

-/* Called with kretprobe_lock held. */
void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
struct pt_regs *regs)
{

--
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