On Wed, Apr 19, 2006 at 03:14:26PM -0700, Anil S Keshavamurthy wrote:
> With this patch Kprobes now registers for page fault notifications only
> when their is an active probe registered. Once all the active probes are
> unregistered their is no need to be notified of page faults and kprobes
> unregisters itself from the page fault notifications. Hence we
> will have ZERO side effects when no probes are active.
This patch isn't complete yet... comments below.
> Signed-off-by: Anil S Keshavamurthy <[email protected]>
> ---
> kernel/kprobes.c | 25 +++++++++++++++++--------
> 1 file changed, 17 insertions(+), 8 deletions(-)
>
> Index: linux-2.6.17-rc1-mm3/kernel/kprobes.c
> ===================================================================
> --- linux-2.6.17-rc1-mm3.orig/kernel/kprobes.c
> +++ linux-2.6.17-rc1-mm3/kernel/kprobes.c
> @@ -47,11 +47,17 @@
>
> static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
> static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];
> +static atomic_t kprobe_count;
>
> 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 notifier_block kprobe_page_fault_nb = {
> + .notifier_call = kprobe_exceptions_notify,
> + .priority = 0x7fffffff /* we need to notified first */
> +};
> +
> #ifdef __ARCH_WANT_KPROBES_INSN_SLOT
> /*
> * kprobe->ainsn.insn points to the copy of the instruction to be
> @@ -464,6 +470,8 @@ static int __kprobes __register_kprobe(s
> old_p = get_kprobe(p->addr);
> if (old_p) {
> ret = register_aggr_kprobe(old_p, p);
> + if (!ret)
> + atomic_inc(&kprobe_count);
> goto out;
> }
>
> @@ -474,6 +482,9 @@ static int __kprobes __register_kprobe(s
> hlist_add_head_rcu(&p->hlist,
> &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);
>
> + if(atomic_add_return(1, &kprobe_count) == 2)
^^^
if (..) please, here and elsewhere
This will not work as desired for i386 (i386 no longer has a kprobe on the
trampoline) and sparc64 (no retprobe support).
> + register_page_fault_notifier(&kprobe_page_fault_nb);
> +
> arch_arm_kprobe(p);
>
> out:
> @@ -523,9 +534,13 @@ valid_p:
> cleanup_p = 0;
> }
>
> + if(atomic_add_return(-1, &kprobe_count) == 1)
> + unregister_page_fault_notifier(&kprobe_page_fault_nb);
Same here - i386 and sparc64 need different checks.
> + else
> + synchronize_rcu();
Why has this changed from synchronize_sched()? This *must* be
synchronize_sched() since, by definition it'll ensure that all
non-preemptive sections are completed. In contrast, synchronize_rcu()
will just enure rcu_read_lock() sections are complete.
As of now, synchronize_sched() is aliased to synchronize_rcu() but I am
told its scheduled to change in the future.
Please revert this back to synchronize_sched().
Thanks,
Ananth
> +
> mutex_unlock(&kprobe_mutex);
>
> - synchronize_sched();
> if (p->mod_refcounted &&
> (mod = module_text_address((unsigned long)p->addr)))
> module_put(mod);
> @@ -544,10 +559,6 @@ static struct notifier_block kprobe_exce
> .priority = 0x7fffffff /* we need to notified first */
> };
>
> -static struct notifier_block kprobe_page_fault_nb = {
> - .notifier_call = kprobe_exceptions_notify,
> - .priority = 0x7fffffff /* we need to notified first */
> -};
>
> int __kprobes register_jprobe(struct jprobe *jp)
> {
> @@ -654,14 +665,12 @@ static int __init init_kprobes(void)
> INIT_HLIST_HEAD(&kprobe_table[i]);
> INIT_HLIST_HEAD(&kretprobe_inst_table[i]);
> }
> + atomic_set(&kprobe_count, 0);
>
> err = arch_init_kprobes();
> if (!err)
> err = register_die_notifier(&kprobe_exceptions_nb);
>
> - if (!err)
> - err = register_page_fault_notifier(&kprobe_page_fault_nb);
> -
> return err;
> }
>
>
> --
-
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