From ceb56070359b7329b5678b5d95a376fcb24767be Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Mon, 27 Jun 2016 21:38:11 +0200 Subject: [PATCH] bpf, perf: delay release of BPF prog after grace period Commit dead9f29ddcc ("perf: Fix race in BPF program unregister") moved destruction of BPF program from free_event_rcu() callback to __free_event(), which is problematic if used with tail calls: if prog A is attached as trace event directly, but at the same time present in a tail call map used by another trace event program elsewhere, then we need to delay destruction via RCU grace period since it can still be in use by the program doing the tail call (the prog first needs to be dropped from the tail call map, then trace event with prog A attached destroyed, so we get immediate destruction). Fixes: dead9f29ddcc ("perf: Fix race in BPF program unregister") Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Cc: Jann Horn Signed-off-by: David S. Miller --- include/linux/bpf.h | 4 ++++ kernel/events/core.c | 2 +- 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/bpf.h b/include/linux/bpf.h index 8269cafc6eb1..0de4de6dd43e 100644 --- a/include/linux/bpf.h +++ b/include/linux/bpf.h @@ -264,6 +264,10 @@ static inline struct bpf_prog *bpf_prog_get(u32 ufd) static inline void bpf_prog_put(struct bpf_prog *prog) { } + +static inline void bpf_prog_put_rcu(struct bpf_prog *prog) +{ +} #endif /* CONFIG_BPF_SYSCALL */ /* verifier prototypes for helper functions called from eBPF programs */ diff --git a/kernel/events/core.c b/kernel/events/core.c index 274450efea90..d00c47b67a97 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7531,7 +7531,7 @@ static void perf_event_free_bpf_prog(struct perf_event *event) prog = event->tp_event->prog; if (prog) { event->tp_event->prog = NULL; - bpf_prog_put(prog); + bpf_prog_put_rcu(prog); } } -- 2.39.2