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[bpf,1/2] bpf: put uprobe link's path and task in release callback

Message ID 20240328052426.3042617-1-andrii@kernel.org (mailing list archive)
State Superseded
Commit e9c856cabefb71d47b2eeb197f72c9c88e9b45b0
Delegated to: BPF
Headers show
Series [bpf,1/2] bpf: put uprobe link's path and task in release callback | expand

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Commit Message

Andrii Nakryiko March 28, 2024, 5:24 a.m. UTC 
There is no need to delay putting either path or task to deallocation
step. It can be done right after bpf_uprobe_unregister. Between release
and dealloc, there could be still some running BPF programs, but they
don't access either task or path, only data in link->uprobes, so it is
safe to do.

On the other hand, doing path_put() in dealloc callback makes this
dealloc sleepable because path_put() itself might sleep. Which is
problematic due to the need to call uprobe's dealloc through call_rcu(),
which is what is done in the next bug fix patch. So solve the problem by
releasing these resources early.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
---
 kernel/trace/bpf_trace.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org March 29, 2024, 2 a.m. UTC | #1 
Hello:

This series was applied to bpf/bpf.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Wed, 27 Mar 2024 22:24:25 -0700 you wrote:
> There is no need to delay putting either path or task to deallocation
> step. It can be done right after bpf_uprobe_unregister. Between release
> and dealloc, there could be still some running BPF programs, but they
> don't access either task or path, only data in link->uprobes, so it is
> safe to do.
> 
> On the other hand, doing path_put() in dealloc callback makes this
> dealloc sleepable because path_put() itself might sleep. Which is
> problematic due to the need to call uprobe's dealloc through call_rcu(),
> which is what is done in the next bug fix patch. So solve the problem by
> releasing these resources early.
> 
> [...]

Here is the summary with links:
  - [bpf,1/2] bpf: put uprobe link's path and task in release callback
    https://git.kernel.org/bpf/bpf/c/e9c856cabefb
  - [bpf,2/2] bpf: support deferring bpf_link dealloc to after RCU grace period
    https://git.kernel.org/bpf/bpf/c/1a80dbcb2dba

You are awesome, thank you!
diff mbox series

Patch

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 0a5c4efc73c3..0b73fe5f7206 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3157,6 +3157,9 @@  static void bpf_uprobe_multi_link_release(struct bpf_link *link)
 
 	umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
 	bpf_uprobe_unregister(&umulti_link->path, umulti_link->uprobes, umulti_link->cnt);
+	if (umulti_link->task)
+		put_task_struct(umulti_link->task);
+	path_put(&umulti_link->path);
 }
 
 static void bpf_uprobe_multi_link_dealloc(struct bpf_link *link)
@@ -3164,9 +3167,6 @@  static void bpf_uprobe_multi_link_dealloc(struct bpf_link *link)
 	struct bpf_uprobe_multi_link *umulti_link;
 
 	umulti_link = container_of(link, struct bpf_uprobe_multi_link, link);
-	if (umulti_link->task)
-		put_task_struct(umulti_link->task);
-	path_put(&umulti_link->path);
 	kvfree(umulti_link->uprobes);
 	kfree(umulti_link);
 }