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authorSteven Rostedt (VMware) <rostedt@goodmis.org>2017-05-16 14:58:35 -0400
committerSteven Rostedt (VMware) <rostedt@goodmis.org>2017-05-17 21:55:58 -0400
commit545a028190dae4437aac4f86da7c8ab20857647c (patch)
treeb0c28f76813590769ca2bdedf85071f97dc59023
parentb172296b90b799c8b634521c248e9316581c8154 (diff)
kprobes: Document how optimized kprobes are removed from module unload
Thomas discovered a bug where the kprobe trace tests had a race condition where the kprobe_optimizer called from a delayed work queue that does the optimizing and "unoptimizing" of a kprobe, can try to modify the text after it has been freed by the init code. The kprobe trace selftest is a special case, and Thomas and myself investigated to see if there's a chance that this could also be a bug with module unloading, as the code is not obvious to how it handles this. After adding lots of printks, I figured it out. Thomas suggested that this should be commented so that others will not have to go through this exercise again. Link: http://lkml.kernel.org/r/20170516145835.3827d3aa@gandalf.local.home Acked-by: Masami Hiramatsu <mhiramat@kernel.org> Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
-rw-r--r--kernel/kprobes.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 199243bba554..2d2d3a568e4e 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2183,6 +2183,12 @@ static int kprobes_module_callback(struct notifier_block *nb,
* The vaddr this probe is installed will soon
* be vfreed buy not synced to disk. Hence,
* disarming the breakpoint isn't needed.
+ *
+ * Note, this will also move any optimized probes
+ * that are pending to be removed from their
+ * corresponding lists to the freeing_list and
+ * will not be touched by the delayed
+ * kprobe_optimizer work handler.
*/
kill_kprobe(p);
}