Re: [rfc-patch 07/11] Text Edit Lock - kprobes architecture independent support

Roel Kluin
2007-11-17T10:17:44Z

Mathieu Desnoyers wrote:
> Use the mutual exclusion provided by the text edit lock in the kprobes code. It
> allows coherent manipulation of the kernel code by other subsystems.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
> CC: prasanna@in.ibm.com
> CC: ananth@in.ibm.com
> CC: anil.s.keshavamurthy@intel.com
> CC: davem@davemloft.net
> ---
> kernel/kprobes.c | 19 +++++++++++++------
> 1 file changed, 13 insertions(+), 6 deletions(-)
>
> Index: linux-2.6-lttng/kernel/kprobes.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/kprobes.c 2007-09-07 10:12:06.000000000 -0400
> +++ linux-2.6-lttng/kernel/kprobes.c 2007-09-07 10:13:09.000000000 -0400
> @@ -43,6 +43,7 @@
> #include <linux/seq_file.h>
> #include <linux/debugfs.h>
> #include <linux/kdebug.h>
> +#include <linux/memory.h>
>
> #include <asm-generic/sections.h>
> #include <asm/cacheflush.h>
> @@ -568,9 +569,10 @@ static int __kprobes __register_kprobe(s
> goto out;
> }
>
> + kernel_text_lock();
> ret = arch_prepare_kprobe(p);
> if (ret)
> - goto out;
> + goto out_unlock_text;
>
> INIT_HLIST_NODE(&p->hlist);
> hlist_add_head_rcu(&p->hlist,
> @@ -578,7 +580,8 @@ static int __kprobes __register_kprobe(s
>
> if (kprobe_enabled)
> arch_arm_kprobe(p);
> -
> +out_unlock_text:
> + kernel_text_unlock();
> out:
> mutex_unlock(&kprobe_mutex);
>
> @@ -621,8 +624,11 @@ valid_p:
> * enabled - otherwise, the breakpoint would already have
> * been removed. We save on flushing icache.
> */
> - if (kprobe_enabled)
> + if (kprobe_enabled) {
> + kernel_text_lock();
> arch_disarm_kprobe(p);
> + kernel_text_unlock();
> + }
> hlist_del_rcu(&old_p->hlist);
> cleanup_p = 1;
> } else {
> @@ -644,9 +650,7 @@ valid_p:
> list_del_rcu(&p->list);
> kfree(old_p);
> }
> - mutex_lock(&kprobe_mutex);
> arch_remove_kprobe(p);
> - mutex_unlock(&kprobe_mutex);
> } else {
> mutex_lock(&kprobe_mutex);
> if (p->break_handler)
> @@ -717,7 +721,6 @@ static int __kprobes pre_handler_kretpro
> ri->rp = rp;
> ri->task = current;
> 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);
> @@ -940,8 +943,10 @@ static void __kprobes enable_all_kprobes
>
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> + kernel_text_lock();
> hlist_for_each_entry_rcu(p, node, head, hlist)
> arch_arm_kprobe(p);
> + kernel_text_unlock();
> }

isn't it better to put the kernel_text_lock around the for loop?

>
> kprobe_enabled = true;
> @@ -969,10 +974,12 @@ static void __kprobes disable_all_kprobe
> printk(KERN_INFO "Kprobes globally disabled\n");
> for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
> head = &kprobe_table[i];
> + kernel_text_lock();
> hlist_for_each_entry_rcu(p, node, head, hlist) {
> if (!arch_trampoline_kprobe(p))
> arch_disarm_kprobe(p);
> }
> + kernel_text_unlock();
> }

same question here

>
> mutex_unlock(&kprobe_mutex);
>