[PATCH 2/6] uprobes/tracing: Fully initialize uprobe_trace_consumer before uprobe_register()

Oleg Nesterov
2013-01-31T19:22:13Z

probe_event_enable() does uprobe_register() and only after that sets
utc->tu and tu->consumer/flags. This can race with uprobe_dispatcher()
which can miss these assignments or see them out of order. Nothing
really bad can happen, but this doesn't look clean/safe.

And this does not allow to use uprobe_consumer->filter() we are going
to add, it is called by uprobe_register() and it needs utc->tu.

Change this code to initialize everything before uprobe_register(), and
reset tu->consumer/flags if it fails. We can't race with event_disable(),
the caller holds event_mutex, and if we could the code would be wrong
anyway.

In fact I think uprobe_trace_consumer should die, it buys nothing but
complicates the code. We can simply add uprobe_consumer into trace_uprobe.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
kernel/trace/trace_uprobe.c | 13 +++++++------
1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 6563f00..7b75949 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -547,17 +547,18 @@ static int probe_event_enable(struct trace_uprobe *tu, int flag)
return -EINTR;

utc->cons.handler = uprobe_dispatcher;
+ utc->tu = tu;
+ tu->consumer = utc;
+ tu->flags |= flag;
+
ret = uprobe_register(tu->inode, tu->offset, &utc->cons);
if (ret) {
+ tu->consumer = NULL;
+ tu->flags &= ~flag;
kfree(utc);
- return ret;
}

- tu->flags |= flag;
- utc->tu = tu;
- tu->consumer = utc;
-
- return 0;
+ return ret;
}

static void probe_event_disable(struct trace_uprobe *tu, int flag)
--
1.5.5.1