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SubjectRe: [PATCH] Kprobes - use a mutex to protect the instruction pages list.
On Sat, Jul 14, 2007 at 03:51:39PM -0400, Mathieu Desnoyers wrote:
> 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

Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>

Thanks Mathieu

> ---
> 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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