KASAN reports a use-after-free of an unbound worker_pool in node_activate_pending_pwq(): BUG: KASAN: slab-use-after-free in _raw_spin_trylock+0x6d/0x120 Read of size 4 at addr ffff8880089ce000 by task kworker/u22:0/318 CPU: 1 UID: 0 PID: 318 Comm: kworker/u22:0 Not tainted 7.2.0 #1 PREEMPT(lazy) Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 Workqueue: 0x0 (flush-8:0) Call Trace: <TASK> dump_stack_lvl+0x53/0x70 print_report+0xce/0x610 kasan_report+0xce/0x100 _raw_spin_trylock+0x6d/0x120 pwq_dec_nr_in_flight+0x4b4/0xcb0 process_one_work+0x921/0x11a0 worker_thread+0x4d0/0xd20 kthread+0x2de/0x3c0 ret_from_fork+0x3aa/0x620 ret_from_fork_asm+0x1a/0x30 </TASK> Allocated by task 311: alloc_pwq+0x439/0xca0 apply_wqattrs_prepare+0x75e/0xd10 apply_workqueue_attrs_locked+0x44/0xa0 wq_nice_store+0x350/0x450 Freed by task 0: kfree+0x127/0x3b0 rcu_core+0x523/0x1780 handle_softirqs+0x1b3/0x610 Last potentially related work creation: put_unbound_pool+0x3f3/0x7d0 pwq_release_workfn+0x494/0x8e0 kthread_worker_fn+0x1ff/0x790 Canceling the last inactive work skips pwq_dec_nr_active(), so an empty pwq can remain on pending_pwqs when its refcnt reaches zero. pwq_release_workfn() currently puts the pool before removing that pwq. If this drops the last pool reference, the pool can be RCU-freed while the pwq remains reachable, and node_activate_pending_pwq() may trylock the freed pool->lock. Remove the pwq from pending_pwqs before putting the pool.
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| @@ -5294,12 +5294,6 @@ static void pwq_release_workfn(struct kthread_work *work) · 5293 unmodified lines | ||
| 5294 | 5294 | mutex_unlock(&wq->mutex); |
| 5295 | 5295 | } |
| 5296 | 5296 | |
| 5297 | − if (!is_percpu_pool(pool)) { | |
| 5298 | − mutex_lock(&wq_pool_mutex); | |
| 5299 | − put_unbound_pool(pool); | |
| 5300 | − mutex_unlock(&wq_pool_mutex); | |
| 5301 | − } | |
| 5302 | − | |
| 5303 | 5297 | if (!list_empty(&pwq->pending_node)) { |
| 5304 | 5298 | struct wq_node_nr_active *nna = |
| 5305 | 5299 | wq_node_nr_active(pwq->wq, pwq->pool->node); |
| @@ -5309,6 +5303,12 @@ static void pwq_release_workfn(struct kthread_work *work) · 3 unmodified lines | ||
| 5309 | 5303 | raw_spin_unlock_irq(&nna->lock); |
| 5310 | 5304 | } |
| 5311 | 5305 | |
| 5306 | + if (!is_percpu_pool(pool)) { | |
| 5307 | + mutex_lock(&wq_pool_mutex); | |
| 5308 | + put_unbound_pool(pool); | |
| 5309 | + mutex_unlock(&wq_pool_mutex); | |
| 5310 | + } | |
| 5311 | + | |
| 5312 | 5312 | kfree_rcu(pwq, rcu); |
| 5313 | 5313 | |
| 5314 | 5314 | /* |