From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> If a ftrace callback does not supply its own recursion protection and does not set the RECURSION_SAFE flag in its ftrace_ops, then ftrace will make a helper trampoline to do so before calling the callback instead of just calling the callback directly. The default for ftrace_ops is going to change. It will expect that handlers provide their own recursion protection, unless its ftrace_ops states otherwise. Link: https://lkml.kernel.org/r/20201028115613.291169246@xxxxxxxxxxx Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Jiri Kosina <jikos@xxxxxxxxxx> Cc: Miroslav Benes <mbenes@xxxxxxx> Cc: Joe Lawrence <joe.lawrence@xxxxxxxxxx> Cc: live-patching@xxxxxxxxxxxxxxx Reviewed-by: Petr Mladek <pmladek@xxxxxxxx> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> --- kernel/livepatch/patch.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/livepatch/patch.c b/kernel/livepatch/patch.c index b552cf2d85f8..6c0164d24bbd 100644 --- a/kernel/livepatch/patch.c +++ b/kernel/livepatch/patch.c @@ -45,9 +45,13 @@ static void notrace klp_ftrace_handler(unsigned long ip, struct klp_ops *ops; struct klp_func *func; int patch_state; + int bit; ops = container_of(fops, struct klp_ops, fops); + bit = ftrace_test_recursion_trylock(); + if (bit < 0) + return; /* * A variant of synchronize_rcu() is used to allow patching functions * where RCU is not watching, see klp_synchronize_transition(). @@ -117,6 +121,7 @@ static void notrace klp_ftrace_handler(unsigned long ip, unlock: preempt_enable_notrace(); + ftrace_test_recursion_unlock(bit); } /* -- 2.28.0
