From: Masami Hiramatsu (Google) mhiramat@kernel.org
commit 195b9cb5b288fec1c871ef89f78cc9a7461aad3a upstream.
Ensure running fprobe_exit_handler() has finished before calling rethook_free() in the unregister_fprobe() so that caller can free the fprobe right after unregister_fprobe().
unregister_fprobe() ensured that all running fprobe_entry/exit_handler() have finished by calling unregister_ftrace_function() which synchronizes RCU. But commit 5f81018753df ("fprobe: Release rethook after the ftrace_ops is unregistered") changed to call rethook_free() after unregister_ftrace_function(). So call rethook_stop() to make rethook disabled before unregister_ftrace_function() and ensure it again.
Here is the possible code flow that can call the exit handler after unregister_fprobe().
------ CPU1 CPU2 call unregister_fprobe(fp) ... __fprobe_handler() rethook_hook() on probed function unregister_ftrace_function() return from probed function rethook hooks find rh->handler == fprobe_exit_handler call fprobe_exit_handler() rethook_free(): set rh->handler = NULL; return from unreigster_fprobe; call fp->exit_handler() <- (*) ------
(*) At this point, the exit handler is called after returning from unregister_fprobe().
This fixes it as following; ------ CPU1 CPU2 call unregister_fprobe() ... rethook_stop(): set rh->handler = NULL; __fprobe_handler() rethook_hook() on probed function unregister_ftrace_function() return from probed function rethook hooks find rh->handler == NULL return from rethook rethook_free() return from unreigster_fprobe; ------
Link: https://lore.kernel.org/all/168873859949.156157.13039240432299335849.stgit@d...
Fixes: 5f81018753df ("fprobe: Release rethook after the ftrace_ops is unregistered") Cc: stable@vger.kernel.org Signed-off-by: Masami Hiramatsu (Google) mhiramat@kernel.org Reviewed-by: Steven Rostedt (Google) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/rethook.h | 1 + kernel/trace/fprobe.c | 3 +++ kernel/trace/rethook.c | 13 +++++++++++++ 3 files changed, 17 insertions(+)
--- a/include/linux/rethook.h +++ b/include/linux/rethook.h @@ -59,6 +59,7 @@ struct rethook_node { };
struct rethook *rethook_alloc(void *data, rethook_handler_t handler); +void rethook_stop(struct rethook *rh); void rethook_free(struct rethook *rh); void rethook_add_node(struct rethook *rh, struct rethook_node *node); struct rethook_node *rethook_try_get(struct rethook *rh); --- a/kernel/trace/fprobe.c +++ b/kernel/trace/fprobe.c @@ -366,6 +366,9 @@ int unregister_fprobe(struct fprobe *fp) fp->ops.saved_func != fprobe_kprobe_handler)) return -EINVAL;
+ if (fp->rethook) + rethook_stop(fp->rethook); + ret = unregister_ftrace_function(&fp->ops); if (ret < 0) return ret; --- a/kernel/trace/rethook.c +++ b/kernel/trace/rethook.c @@ -54,6 +54,19 @@ static void rethook_free_rcu(struct rcu_ }
/** + * rethook_stop() - Stop using a rethook. + * @rh: the struct rethook to stop. + * + * Stop using a rethook to prepare for freeing it. If you want to wait for + * all running rethook handler before calling rethook_free(), you need to + * call this first and wait RCU, and call rethook_free(). + */ +void rethook_stop(struct rethook *rh) +{ + WRITE_ONCE(rh->handler, NULL); +} + +/** * rethook_free() - Free struct rethook. * @rh: the struct rethook to be freed. *