Messages in this thread Patch in this message | | | From | Petr Mladek <> | Subject | [PATCH] workqueue: Make create_worker() safe against spurious wakeups | Date | Wed, 22 Jun 2022 16:08:53 +0200 |
| |
A system crashed with the following BUG() report:
[115147.050484] BUG: kernel NULL pointer dereference, address: 0000000000000000 [115147.050488] #PF: supervisor write access in kernel mode [115147.050489] #PF: error_code(0x0002) - not-present page [115147.050490] PGD 0 P4D 0 [115147.050494] Oops: 0002 [#1] PREEMPT_RT SMP NOPTI [115147.050498] CPU: 1 PID: 16213 Comm: kthreadd Kdump: loaded Tainted: G O X 5.3.18-2-rt #1 SLE15-SP2 (unreleased) [115147.050510] RIP: 0010:_raw_spin_lock_irq+0x14/0x30 [115147.050513] Code: 89 c6 e8 5f 7a 9b ff 66 90 c3 66 66 2e 0f 1f 84 00 00 00 00 00 90 0f 1f 44 00 00 fa 65 ff 05 fb 53 6c 55 31 c0 ba 01 00 00 00 <f0> 0f b1 17 75 01 c3 89 c6 e8 2e 7a 9b ff 66 90 c3 90 90 90 90 90 [115147.050514] RSP: 0018:ffffb0f68822fed8 EFLAGS: 00010046 [115147.050515] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 [115147.050516] RDX: 0000000000000001 RSI: 0000000000000002 RDI: 0000000000000000 [115147.050517] RBP: ffff9ca73af40a40 R08: 0000000000000001 R09: 0000000000027340 [115147.050519] R10: ffffb0f68822fe70 R11: 00000000000000a9 R12: ffffb0f688067dc0 [115147.050520] R13: ffff9ca77e9a8000 R14: ffff9ca7634ca780 R15: ffff9ca7634ca780 [115147.050521] FS: 0000000000000000(0000) GS:ffff9ca77fb00000(0000) knlGS:0000000000000000 [115147.050523] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [115147.050524] CR2: 00000000000000b8 CR3: 000000004472e000 CR4: 00000000003406e0 [115147.050524] Call Trace: [115147.050533] worker_thread+0xb4/0x3c0 [115147.050538] ? process_one_work+0x4a0/0x4a0 [115147.050540] kthread+0x152/0x170 [115147.050542] ? kthread_park+0xa0/0xa0 [115147.050544] ret_from_fork+0x35/0x40
Further debugging shown that the worker thread was woken before worker_attach_to_pool() finished in create_worker().
Any kthread is supposed to stay in TASK_UNINTERRUPTIBLE sleep until it is explicitly woken. But a spurious wakeup might break this expectation.
As a result, worker_thread() might read worker->pool before it was set in worker create_worker() by worker_attach_to_pool(). Also manage_workers() might want to create yet another worker before worker->pool->nr_workers is updated. It is a kind off a chicken & egg problem.
Synchronize these operations using a completion API.
Note that worker->pool might be then read without wq_pool_attach_mutex. Normal worker always belongs to the same pool.
Also note that rescuer_thread() does not need this because all needed values are set before the kthreads is created. It is connected with a particular workqueue. It is attached to different pools when needed.
Signed-off-by: Petr Mladek <pmladek@suse.com> --- kernel/workqueue.c | 13 ++++++++++++- kernel/workqueue_internal.h | 1 + 2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 1ea50f6be843..9586b0797145 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1939,6 +1939,7 @@ static struct worker *create_worker(struct worker_pool *pool) goto fail; worker->id = id; + init_completion(&worker->ready_to_start); if (pool->cpu >= 0) snprintf(id_buf, sizeof(id_buf), "%d:%d%s", pool->cpu, id, @@ -1961,6 +1962,7 @@ static struct worker *create_worker(struct worker_pool *pool) raw_spin_lock_irq(&pool->lock); worker->pool->nr_workers++; worker_enter_idle(worker); + complete(&worker->ready_to_start); wake_up_process(worker->task); raw_spin_unlock_irq(&pool->lock); @@ -2378,10 +2380,19 @@ static void set_pf_worker(bool val) static int worker_thread(void *__worker) { struct worker *worker = __worker; - struct worker_pool *pool = worker->pool; + struct worker_pool *pool; /* tell the scheduler that this is a workqueue worker */ set_pf_worker(true); + + /* + * Wait until the worker is ready to get started. It must be attached + * to a pool first. This is needed because of spurious wakeups. + */ + while (wait_for_completion_interruptible(&worker->ready_to_start)) + ; + pool = worker->pool; + woke_up: raw_spin_lock_irq(&pool->lock); diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h index e00b1204a8e9..ffca2783c8bf 100644 --- a/kernel/workqueue_internal.h +++ b/kernel/workqueue_internal.h @@ -41,6 +41,7 @@ struct worker { /* L: for rescuers */ struct list_head node; /* A: anchored at pool->workers */ /* A: runs through worker->node */ + struct completion ready_to_start; /* None: handle spurious wakeup */ unsigned long last_active; /* L: last active timestamp */ unsigned int flags; /* X: flags */ -- 2.35.3
| |