Re: [PATCH] KEYS: dispatch key_gc_work to system_wq.

[Jarkko Sakkinen <jarkko@kernel.org>]

short summary: /system_wq/system_dfl_long_wq/, /\.//

On Mon, Oct 26, 2026 at 05:12:18AM +0200, Jarkko Sakkinen wrote:
> schedule_work() dispatches key_gc_work on the per-CPU system_wq, which can
> choke the queue:
> 
> BUG: workqueue lockup - pool cpus=0 node=0 flags=0x2 nice=0 stuck for 30s!
> 
> Queue the work on system_dfl_long_wq instead, which is an unbounded wq for
> long-running tasks i.e., it has the WQ_BOUND flag set and thus cannot hog
> the CPU core.
> 
> Link: https://lore.kernel.org/keyrings/20261024042944.52493-1-hackerowskiy@gmail.com/
> Reported-by: syzbot+c15de43f1e7fffbb7b9b@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/all/6ad35b60.7952420f.283480.0360.GAE@google.com/T/
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> I sanity checked with perf that scheduler latency improved clearly as it
> should, and used large keyrings that I expired, as the test payload.
> 
> It was ad-hoc testing but I can scrape from transcripts a test script
> if wanted.
>  security/keys/gc.c  | 8 ++++----
>  security/keys/key.c | 2 +-
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/security/keys/gc.c b/security/keys/gc.c
> index eda445f815d4..2337d39722e4 100644
> --- a/security/keys/gc.c
> +++ b/security/keys/gc.c
> @@ -57,7 +57,7 @@ void key_schedule_gc(time64_t gc_at)
>  
>  	if (gc_at <= now || test_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags)) {
>  		kdebug("IMMEDIATE");
> -		schedule_work(&key_gc_work);
> +		queue_work(system_dfl_long_wq, &key_gc_work);
>  	} else if (gc_at < key_gc_next_run) {
>  		kdebug("DEFERRED");
>  		key_gc_next_run = gc_at;
> @@ -85,7 +85,7 @@ void key_set_expiry(struct key *key, time64_t expiry)
>  void key_schedule_gc_links(void)
>  {
>  	set_bit(KEY_GC_KEY_EXPIRED, &key_gc_flags);
> -	schedule_work(&key_gc_work);
> +	queue_work(system_dfl_long_wq, &key_gc_work);
>  }
>  
>  /*
> @@ -119,7 +119,7 @@ void key_gc_keytype(struct key_type *ktype)
>  	set_bit(KEY_GC_REAP_KEYTYPE, &key_gc_flags);
>  
>  	kdebug("schedule");
> -	schedule_work(&key_gc_work);
> +	queue_work(system_dfl_long_wq, &key_gc_work);
>  
>  	kdebug("sleep");
>  	wait_on_bit(&key_gc_flags, KEY_GC_REAPING_KEYTYPE,
> @@ -322,7 +322,7 @@ static void key_garbage_collector(struct work_struct *work)
>  	}
>  
>  	if (gc_state & KEY_GC_REAP_AGAIN)
> -		schedule_work(&key_gc_work);
> +		queue_work(system_dfl_long_wq, &key_gc_work);
>  	kleave(" [end %x]", gc_state);
>  	return;
>  
> diff --git a/security/keys/key.c b/security/keys/key.c
> index 6ebb8691551f..599626c897b2 100644
> --- a/security/keys/key.c
> +++ b/security/keys/key.c
> @@ -668,7 +668,7 @@ void key_put(struct key *key)
>  			}
>  			/* Mark key as safe for GC after key->user done. */
>  			clear_bit_unlock(KEY_FLAG_USER_ALIVE, &key->flags);
> -			schedule_work(&key_gc_work);
> +			queue_work(system_dfl_long_wq, &key_gc_work);
>  		}
>  	}
>  }
> -- 
> 2.47.3
> 

Br, Jarkko