[PATCH v1 net] af_unix: Set gc_in_progress to true in unix_gc().

[PATCH v1 net] af_unix: Set gc_in_progress to true in unix_gc().

[Kuniyuki Iwashima]

Igor Ushakov reported that unix_gc() could run with gc_in_progress
being false if the work is scheduled while running:

  Thread 1         Thread 2                     Thread 3
  --------         --------                     --------
                   unix_schedule_gc()           unix_schedule_gc()
                   `- if (!gc_in_progress)      `- if (!gc_in_progress)
                      |- gc_in_progress = true     |
                      `- queue_work()              |
  unix_gc() <----------------/                     |
  |                                                |- gc_in_progress = true
  ...                                              `- queue_work()
  |                                                       |
  `- gc_in_progress = false                               |
                                                          |
  unix_gc() <---------------------------------------------'
  |
  ... /* gc_in_progress == false */
  |
  `- gc_in_progress = false

unix_peek_fpl() relies on gc_in_progress not to confuse GC
by MSG_PEEK.

Let's set gc_in_progress to true in unix_gc().

Fixes: 8b90a9f819dc ("af_unix: Run GC on only one CPU.")
Reported-by: Igor Ushakov <sysroot314@gmail.com>
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/unix/garbage.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/unix/garbage.c b/net/unix/garbage.c
index a7967a345827..0783555e2526 100644
--- a/net/unix/garbage.c
+++ b/net/unix/garbage.c
@@ -607,6 +607,8 @@ static void unix_gc(struct work_struct *work)
 	struct sk_buff_head hitlist;
 	struct sk_buff *skb;
 
+	WRITE_ONCE(gc_in_progress, true);
+
 	spin_lock(&unix_gc_lock);
 
 	if (unix_graph_state == UNIX_GRAPH_NOT_CYCLIC) {
@@ -649,10 +651,8 @@ void unix_schedule_gc(struct user_struct *user)
 	    READ_ONCE(user->unix_inflight) < UNIX_INFLIGHT_SANE_USER)
 		return;
 
-	if (!READ_ONCE(gc_in_progress)) {
-		WRITE_ONCE(gc_in_progress, true);
+	if (!READ_ONCE(gc_in_progress))
 		queue_work(system_dfl_wq, &unix_gc_work);
-	}
 
 	if (user && READ_ONCE(unix_graph_cyclic_sccs))
 		flush_work(&unix_gc_work);
-- 
2.54.0.545.g6539524ca2-goog

Re: [PATCH v1 net] af_unix: Set gc_in_progress to true in unix_gc().

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Fri,  1 May 2026 07:39:41 +0000 you wrote:
> Igor Ushakov reported that unix_gc() could run with gc_in_progress
> being false if the work is scheduled while running:
> 
>   Thread 1         Thread 2                     Thread 3
>   --------         --------                     --------
>                    unix_schedule_gc()           unix_schedule_gc()
>                    `- if (!gc_in_progress)      `- if (!gc_in_progress)
>                       |- gc_in_progress = true     |
>                       `- queue_work()              |
>   unix_gc() <----------------/                     |
>   |                                                |- gc_in_progress = true
>   ...                                              `- queue_work()
>   |                                                       |
>   `- gc_in_progress = false                               |
>                                                           |
>   unix_gc() <---------------------------------------------'
>   |
>   ... /* gc_in_progress == false */
>   |
>   `- gc_in_progress = false
> 
> [...]

Here is the summary with links:
  - [v1,net] af_unix: Set gc_in_progress to true in unix_gc().
    https://git.kernel.org/netdev/net/c/d82ba05263c6

You are awesome, thank you!
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