Commit c0f3bb40 authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google) Committed by Daniel Borkmann

rethook: Reject getting a rethook if RCU is not watching

Since the rethook_recycle() will involve the call_rcu() for reclaiming
the rethook_instance, the rethook must be set up at the RCU available
context (non idle). This rethook_recycle() in the rethook trampoline
handler is inevitable, thus the RCU available check must be done before
setting the rethook trampoline.

This adds a rcu_is_watching() check in the rethook_try_get() so that
it will return NULL if it is called when !rcu_is_watching().

Fixes: 54ecbe6f ("rethook: Add a generic return hook")
Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/bpf/165461827269.280167.7379263615545598958.stgit@devnote2
parent c88dbbcd
......@@ -154,6 +154,15 @@ struct rethook_node *rethook_try_get(struct rethook *rh)
if (unlikely(!handler))
return NULL;
/*
* This expects the caller will set up a rethook on a function entry.
* When the function returns, the rethook will eventually be reclaimed
* or released in the rethook_recycle() with call_rcu().
* This means the caller must be run in the RCU-availabe context.
*/
if (unlikely(!rcu_is_watching()))
return NULL;
fn = freelist_try_get(&rh->pool);
if (!fn)
return NULL;
......
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