Messages in this thread | | | From | Lai Jiangshan <> | Date | Thu, 4 Aug 2022 16:57:01 +0800 | Subject | Re: [PATCH] workqueue: Make create_worker() safe against spurious wakeups |
| |
On Wed, Jun 22, 2022 at 10:10 PM Petr Mladek <pmladek@suse.com> wrote: > > 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)) > + ;
There might be some wakeups from wake_up_worker() since it is in the idle list. These wakeups will be "spurious wakeups" in the view of the completion subsystem.
> + 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 >
| |