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