linux-kernel - [PATCH trace/for-next 3/3] bpf: ensure RCU Tasks Trace GP for sleepable raw tracepoint BPF links

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Message-ID: <20241031210938.1696639-3-andrii@kernel.org>
Date: Thu, 31 Oct 2024 14:09:38 -0700
From: Andrii Nakryiko <andrii@...nel.org>
To: linux-trace-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	rostedt@...dmis.org,
	ast@...nel.org,
	daniel@...earbox.net,
	martin.lau@...nel.org
Cc: mathieu.desnoyers@...icios.com,
	linux-kernel@...r.kernel.org,
	mhiramat@...nel.org,
	peterz@...radead.org,
	paulmck@...nel.org,
	jrife@...gle.com,
	Andrii Nakryiko <andrii@...nel.org>
Subject: [PATCH trace/for-next 3/3] bpf: ensure RCU Tasks Trace GP for sleepable raw tracepoint BPF links

Now that kernel supports sleepable tracepoints, the fact that
bpf_probe_unregister() is asynchronous, i.e., that it doesn't wait for
any in-flight tracepoints to conclude before returning, we now need to
delay BPF raw tp link's deallocation and bpf_prog_put() of its
underlying BPF program (regardless of program's own sleepable semantics)
until after full RCU Tasks Trace GP. With that GP over, we'll have
a guarantee that no tracepoint can reach BPF link and thus its BPF program.

We use newly added tracepoint_is_faultable() check to know when this RCU
Tasks Trace GP is necessary and utilize BPF link's own sleepable flag
passed through bpf_link_init_sleepable() initializer.

Reported-by: Jordan Rife <jrife@...gle.com>
Fixes: a363d27cdbc2 ("tracing: Allow system call tracepoints to handle page faults")
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
---
 kernel/bpf/syscall.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 0f5540627911..db2a987504b2 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -35,6 +35,7 @@
 #include <linux/rcupdate_trace.h>
 #include <linux/memcontrol.h>
 #include <linux/trace_events.h>
+#include <linux/tracepoint.h>
 
 #include <net/netfilter/nf_bpf_link.h>
 #include <net/netkit.h>
@@ -3845,8 +3846,9 @@ static int bpf_raw_tp_link_attach(struct bpf_prog *prog,
 		err = -ENOMEM;
 		goto out_put_btp;
 	}
-	bpf_link_init(&link->link, BPF_LINK_TYPE_RAW_TRACEPOINT,
-		      &bpf_raw_tp_link_lops, prog);
+	bpf_link_init_sleepable(&link->link, BPF_LINK_TYPE_RAW_TRACEPOINT,
+				&bpf_raw_tp_link_lops, prog,
+				tracepoint_is_faultable(btp->tp));
 	link->btp = btp;
 	link->cookie = cookie;
 
-- 
2.43.5