netdev - [PATCH v2 bpf-next] bpf: abstract away entire bpf

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Date:   Thu, 12 Mar 2020 17:21:28 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH v2 bpf-next] bpf: abstract away entire bpf_link clean up procedure

Instead of requiring users to do three steps for cleaning up bpf_link, its
anon_inode file, and unused fd, abstract that away into bpf_link_cleanup()
helper. bpf_link_defunct() is removed, as it shouldn't be needed as an
individual operation anymore.

v1->v2:
- keep bpf_link_cleanup() static for now (Daniel).

Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 include/linux/bpf.h  |  1 -
 kernel/bpf/syscall.c | 18 +++++++++++-------
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 4fd91b7c95ea..49389ddb948f 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1075,7 +1075,6 @@ struct bpf_link_ops {
 
 void bpf_link_init(struct bpf_link *link, const struct bpf_link_ops *ops,
 		   struct bpf_prog *prog);
-void bpf_link_defunct(struct bpf_link *link);
 void bpf_link_inc(struct bpf_link *link);
 void bpf_link_put(struct bpf_link *link);
 int bpf_link_new_fd(struct bpf_link *link);
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index b2f73ecacced..85567a6ea5f9 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2188,9 +2188,17 @@ void bpf_link_init(struct bpf_link *link, const struct bpf_link_ops *ops,
 	link->prog = prog;
 }
 
-void bpf_link_defunct(struct bpf_link *link)
+/* Clean up bpf_link and corresponding anon_inode file and FD. After
+ * anon_inode is created, bpf_link can't be just kfree()'d due to deferred
+ * anon_inode's release() call. This helper manages marking bpf_link as
+ * defunct, releases anon_inode file and puts reserved FD.
+ */
+static void bpf_link_cleanup(struct bpf_link *link, struct file *link_file,
+			     int link_fd)
 {
 	link->prog = NULL;
+	fput(link_file);
+	put_unused_fd(link_fd);
 }
 
 void bpf_link_inc(struct bpf_link *link)
@@ -2383,9 +2391,7 @@ static int bpf_tracing_prog_attach(struct bpf_prog *prog)
 
 	err = bpf_trampoline_link_prog(prog);
 	if (err) {
-		bpf_link_defunct(&link->link);
-		fput(link_file);
-		put_unused_fd(link_fd);
+		bpf_link_cleanup(&link->link, link_file, link_fd);
 		goto out_put_prog;
 	}
 
@@ -2498,9 +2504,7 @@ static int bpf_raw_tracepoint_open(const union bpf_attr *attr)
 
 	err = bpf_probe_register(link->btp, prog);
 	if (err) {
-		bpf_link_defunct(&link->link);
-		fput(link_file);
-		put_unused_fd(link_fd);
+		bpf_link_cleanup(&link->link, link_file, link_fd);
 		goto out_put_btp;
 	}
 
-- 
2.17.1