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

[Oleg Nesterov]

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@xxxxxxxxxx>
Acked-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
 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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/