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authorSrinivasa D S <srinivasa@in.ibm.com>2008-07-25 01:46:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-25 10:53:30 -0700
commitef53d9c5e4da147ecaa43c44c5e5945eb83970a2 (patch)
tree3b596445e5d0613fda4b33a4ae96e0e3fffdcf1e /kernel
parent53a9600c634e3bfd6230e0597aca159bf4d4d010 (diff)
kprobes: improve kretprobe scalability with hashed locking
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 ========================= Signed-off-by: Srinivasa DS <srinivasa@in.ibm.com> Signed-off-by: Jim Keniston <jkenisto@us.ibm.com> Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com> Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com> Cc: David S. Miller <davem@davemloft.net> Cc: Masami Hiramatsu <mhiramat@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/kprobes.c127
1 files changed, 89 insertions, 38 deletions
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 1485ca8d0e00..cb0b3bde3617 100644
--- a/kernel/kprobes.c
+++ b/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_table[KPROBE_TABLE_SIZE];
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(struct kprobe *p)
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 task_struct *tk)
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 kretprobe *rp)
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);
}
@@ -831,32 +875,37 @@ 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;
+ 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;
}
@@ -892,7 +941,7 @@ static int __kprobes __register_kretprobe(struct kretprobe *rp,
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) +
@@ -901,8 +950,8 @@ static int __kprobes __register_kretprobe(struct kretprobe *rp,
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;
@@ -1009,6 +1058,7 @@ 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));
}
/*
@@ -1050,6 +1100,7 @@ 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();