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Subject[patch 02/11] Kprobes - use a mutex to protect the instruction pages list.
Protect the instruction pages list by a specific insn pages mutex, called in 
get_insn_slot() and free_insn_slot(). It makes sure that architectures that does
not need to call arch_remove_kprobe() does not take an unneeded kprobes mutex.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
CC: hch@infradead.org
CC: prasanna@in.ibm.com
CC: ananth@in.ibm.com
CC: anil.s.keshavamurthy@intel.com
CC: davem@davemloft.net
---
kernel/kprobes.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
Index: linux-2.6-lttng/kernel/kprobes.c
===================================================================
--- linux-2.6-lttng.orig/kernel/kprobes.c 2007-07-14 15:47:19.000000000 -0400
+++ linux-2.6-lttng/kernel/kprobes.c 2007-07-14 15:48:51.000000000 -0400
@@ -101,6 +101,10 @@ enum kprobe_slot_state {
SLOT_USED = 2,
};

+/*
+ * Protects the kprobe_insn_pages list. Can nest into kprobe_mutex.
+ */
+static DEFINE_MUTEX(kprobe_insn_mutex);
static struct hlist_head kprobe_insn_pages;
static int kprobe_garbage_slots;
static int collect_garbage_slots(void);
@@ -137,7 +141,9 @@ kprobe_opcode_t __kprobes *get_insn_slot
{
struct kprobe_insn_page *kip;
struct hlist_node *pos;
+ kprobe_opcode_t *ret;

+ mutex_lock(&kprobe_insn_mutex);
retry:
hlist_for_each_entry(kip, pos, &kprobe_insn_pages, hlist) {
if (kip->nused < INSNS_PER_PAGE) {
@@ -146,7 +152,8 @@ kprobe_opcode_t __kprobes *get_insn_slot
if (kip->slot_used[i] == SLOT_CLEAN) {
kip->slot_used[i] = SLOT_USED;
kip->nused++;
- return kip->insns + (i * MAX_INSN_SIZE);
+ ret = kip->insns + (i * MAX_INSN_SIZE);
+ goto end;
}
}
/* Surprise! No unused slots. Fix kip->nused. */
@@ -160,8 +167,10 @@ kprobe_opcode_t __kprobes *get_insn_slot
}
/* 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;
+ if (!kip) {
+ ret = NULL;
+ goto end;
+ }

/*
* Use module_alloc so this page is within +/- 2GB of where the
@@ -171,7 +180,8 @@ kprobe_opcode_t __kprobes *get_insn_slot
kip->insns = module_alloc(PAGE_SIZE);
if (!kip->insns) {
kfree(kip);
- return NULL;
+ ret = NULL;
+ goto end;
}
INIT_HLIST_NODE(&kip->hlist);
hlist_add_head(&kip->hlist, &kprobe_insn_pages);
@@ -179,7 +189,10 @@ kprobe_opcode_t __kprobes *get_insn_slot
kip->slot_used[0] = SLOT_USED;
kip->nused = 1;
kip->ngarbage = 0;
- return kip->insns;
+ ret = kip->insns;
+end:
+ mutex_unlock(&kprobe_insn_mutex);
+ return ret;
}

/* Return 1 if all garbages are collected, otherwise 0. */
@@ -213,7 +226,7 @@ static int __kprobes collect_garbage_slo
struct kprobe_insn_page *kip;
struct hlist_node *pos, *next;

- /* Ensure no-one is preepmted on the garbages */
+ /* Ensure no-one is preempted on the garbages */
if (check_safety() != 0)
return -EAGAIN;

@@ -237,6 +250,7 @@ void __kprobes free_insn_slot(kprobe_opc
struct kprobe_insn_page *kip;
struct hlist_node *pos;

+ mutex_lock(&kprobe_insn_mutex);
hlist_for_each_entry(kip, pos, &kprobe_insn_pages, hlist) {
if (kip->insns <= slot &&
slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
@@ -253,6 +267,7 @@ void __kprobes free_insn_slot(kprobe_opc

if (dirty && ++kprobe_garbage_slots > INSNS_PER_PAGE)
collect_garbage_slots();
+ mutex_unlock(&kprobe_insn_mutex);
}
#endif

--
Mathieu Desnoyers
Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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