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

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Message-ID: <CAPhsuW5g1dOnceA=kqfpC+rR6EguJaR+wPwY9nSWLbGSSj5XjQ@mail.gmail.com>
Date:   Sat, 11 Aug 2018 01:12:58 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     srikar@...ux.vnet.ibm.com, Oleg Nesterov <oleg@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, mhiramat@...nel.org,
        Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
        acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org,
        open list <linux-kernel@...r.kernel.org>,
        ananth@...ux.vnet.ibm.com,
        Alexis Berlemont <alexis.berlemont@...il.com>,
        naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com
Subject: Re: [PATCH v8 5/6] trace_uprobe/sdt: Prevent multiple reference
 counter for same uprobe

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@...ux.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@...ux.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
>