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SubjectRe: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c
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> On Apr 18, 2018, at 7:25 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Wed, 18 Apr 2018 16:03:42 +0200
> Miklos Szeredi <miklos@szeredi.hu> wrote:
>
>>> @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>>> goto err_flags;
>>>
>>> tu->consumer.filter = filter;
>>> - ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>>> + ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>>> + &tu->consumer);
>>
>> It is not entirely clear how the lifetime of uprobe relates to the
>> lifetime of trace_uprobe. Is the uprobe object never going to survive
>> its creator trace_uprobe object?
>
> Not exactly sure what you mean here.
>
> 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?
>
> -- Steve
>

Just as Miklos pointed out, I run tests with the uprobe and confirmed
that igrab() is not sufficient to prevent umount. When we change it to
path_get()/path_put(), umount will abort because of the trace_uprobe.

Song


>>
>> If that's the case, it warrants a comment. If that's not the case,
>> then the path would need to be passed to uprobe_resister() which would
>> need to obtain its own reference.
>>
>>> if (ret)
>>> goto err_buffer;
>>>

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