Re: [PATCH v8 5/6] trace_uprobe/sdt: Prevent multiple reference counter for same uprobe

Song Liu
2018-08-11T08:13:03Z

Do we really need this given we already have PATCH 4/6?
uprobe_regsiter() can be called
out of trace_uprobe, this patch won't catch all conflicts anyway.

Song

On Wed, Aug 8, 2018 at 9:18 PM, Ravi Bangoria
<ravi.bangoria@linux.ibm.com> wrote:
> We assume to have only one reference counter for one uprobe.
> Don't allow user to add multiple trace_uprobe entries having
> same inode+offset but different reference counter.
>
> Ex,
> # echo "p:sdt_tick/loop2 /home/ravi/tick:0x6e4(0x10036)" > uprobe_events
> # echo "p:sdt_tick/loop2_1 /home/ravi/tick:0x6e4(0xfffff)" >> uprobe_events
> bash: echo: write error: Invalid argument
>
> # dmesg
> trace_kprobe: Reference counter offset mismatch.
>
> There is one exception though:
> When user is trying to replace the old entry with the new
> one, we allow this if the new entry does not conflict with
> any other existing entries.
>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
> ---
> kernel/trace/trace_uprobe.c | 37 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index bf2be098eb08..be64d943d7ea 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -324,6 +324,35 @@ static int unregister_trace_uprobe(struct trace_uprobe *tu)
> return 0;
> }
>
> +/*
> + * Uprobe with multiple reference counter is not allowed. i.e.
> + * If inode and offset matches, reference counter offset *must*
> + * match as well. Though, there is one exception: If user is
> + * replacing old trace_uprobe with new one(same group/event),
> + * then we allow same uprobe with new reference counter as far
> + * as the new one does not conflict with any other existing
> + * ones.
> + */
> +static struct trace_uprobe *find_old_trace_uprobe(struct trace_uprobe *new)
> +{
> + struct trace_uprobe *tmp, *old = NULL;
> + struct inode *new_inode = d_real_inode(new->path.dentry);
> +
> + old = find_probe_event(trace_event_name(&new->tp.call),
> + new->tp.call.class->system);
> +
> + list_for_each_entry(tmp, &uprobe_list, list) {
> + if ((old ? old != tmp : true) &&
> + new_inode == d_real_inode(tmp->path.dentry) &&
> + new->offset == tmp->offset &&
> + new->ref_ctr_offset != tmp->ref_ctr_offset) {
> + pr_warn("Reference counter offset mismatch.");
> + return ERR_PTR(-EINVAL);
> + }
> + }
> + return old;
> +}
> +
> /* Register a trace_uprobe and probe_event */
> static int register_trace_uprobe(struct trace_uprobe *tu)
> {
> @@ -333,8 +362,12 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
> mutex_lock(&uprobe_lock);
>
> /* register as an event */
> - old_tu = find_probe_event(trace_event_name(&tu->tp.call),
> - tu->tp.call.class->system);
> + old_tu = find_old_trace_uprobe(tu);
> + if (IS_ERR(old_tu)) {
> + ret = PTR_ERR(old_tu);
> + goto end;
> + }
> +
> if (old_tu) {
> /* delete old event */
> ret = unregister_trace_uprobe(old_tu);
> --
> 2.14.4
>