[lkml]   [2018]   [Apr]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c
On Wed, 18 Apr 2018 16:40:19 +0200
Miklos Szeredi <> wrote:

> > The trace_uprobe (the probe event) is created, it doesn't do anything
> > until it is enabled. This function is called when it is enabled. The
> > trace_uprobe (probe event) can not be deleted while it is enabled
> > (EBUSY).
> >
> > Are you asking what happens if the file is deleted while it has probe?
> > That I don't know about (haven't tried it out). But I would hope that
> > it keeps a reference to the inode, isn't that what the igrab is for?
> > And is now being replaced by a reference on the path, or is that the
> > problem?
> No, that's not the problem.
> What I don't see is how the uprobe object relates to the trace_uprobe object.
> Because after the patch the uprobe object still only has a ref to the
> inode, and that can lead to the same issue as with trace_uprobe.
> OTOH if uprobe can't survive its creating trace_uprobe, then it
> doesn't need to take a ref to the inode at all, since trace_uprobe
> already holds it. Taking an extra ref isn't incorrect, it's just
> unnecessary and confusing.
> So this needs to be cleared up in some way.

The uprobe created by the trace_uprobe creation must be deleted before
the trace_uprobe can be deleted. Basically we have this:

# cd /sys/kernel/tracing
# echo "uprobe creation text" > uprobe_events

The trace_uprobe is created (but not the uprobe itself). This is what
calls create_trace_uprobe().

# echo 1 > events/uprobes/enable

This enables all the trace uprobe events, which creates the uprobes.
This is the action that calls probe_event_enable(), which creates

At this point, any write to uprobe_events that would destroy the trace
uprobes would return with -EBUSY, and the trace uprobes will not be

# echo 0 > events/uprobes/enable

This will call the probe_event_disable() which will call
uprobe_unregister() which will destroy the uprobe.

Now we can delete the trace uprobe.

Does that answer your question? A uprobe created for trace uprobes can
not survive the trace uprobe itself.

-- Steve

 \ /
  Last update: 2018-04-18 17:19    [W:0.041 / U:20.248 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site