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io-wq: ensure we have a stable view of ->cur_work for cancellations 

worker->cur_work is currently protected by the lock of the wqe that the
worker belongs to. When we send a signal to a worker, we need a stable
view of ->cur_work, so we need to hold that lock. But this doesn't work
so well, since we have the opposite order potentially on queueing work.
If POLL_ADD is used with a signalfd, then io_poll_wake() is called with
the signal lock, and that sometimes needs to insert work items.

Add a specific worker lock that protects the current work item. Then we
can guarantee that the task we're sending a signal is currently
processing the exact work we think it is.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2019-11-13 09:43:34 -07:00
parent 7d7230652e
commit 36c2f9223e
1 changed files with 28 additions and 19 deletions
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47
fs/io-wq.c
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@ -49,7 +49,9 @@ struct io_worker {
struct task_struct *task;
wait_queue_head_t wait;
struct io_wqe *wqe;
struct io_wq_work *cur_work;
spinlock_t lock;
struct rcu_head rcu;
struct mm_struct *mm;
@ -323,7 +325,6 @@ static void __io_worker_busy(struct io_wqe *wqe, struct io_worker *worker,
hlist_nulls_add_head_rcu(&worker->nulls_node,
&wqe->busy_list.head);
}
worker->cur_work = work;
/*
* If worker is moving from bound to unbound (or vice versa), then
@ -402,17 +403,6 @@ static void io_worker_handle_work(struct io_worker *worker)
do {
unsigned hash = -1U;
/*
* Signals are either sent to cancel specific work, or to just
* cancel all work items. For the former, ->cur_work must
* match. ->cur_work is NULL at this point, since we haven't
* assigned any work, so it's safe to flush signals for that
* case. For the latter case of cancelling all work, the caller
* wil have set IO_WQ_BIT_CANCEL.
*/
if (signal_pending(current))
flush_signals(current);
/*
* If we got some work, mark us as busy. If we didn't, but
* the list isn't empty, it means we stalled on hashed work.
@ -432,6 +422,14 @@ static void io_worker_handle_work(struct io_worker *worker)
if (!work)
break;
next:
/* flush any pending signals before assigning new work */
if (signal_pending(current))
flush_signals(current);
spin_lock_irq(&worker->lock);
worker->cur_work = work;
spin_unlock_irq(&worker->lock);
if ((work->flags & IO_WQ_WORK_NEEDS_FILES) &&
current->files != work->files) {
task_lock(current);
@ -457,8 +455,12 @@ next:
old_work = work;
work->func(&work);
spin_lock_irq(&wqe->lock);
spin_lock_irq(&worker->lock);
worker->cur_work = NULL;
spin_unlock_irq(&worker->lock);
spin_lock_irq(&wqe->lock);
if (hash != -1U) {
wqe->hash_map &= ~BIT_ULL(hash);
wqe->flags &= ~IO_WQE_FLAG_STALLED;
@ -577,6 +579,7 @@ static void create_io_worker(struct io_wq *wq, struct io_wqe *wqe, int index)
worker->nulls_node.pprev = NULL;
init_waitqueue_head(&worker->wait);
worker->wqe = wqe;
spin_lock_init(&worker->lock);
worker->task = kthread_create_on_node(io_wqe_worker, worker, wqe->node,
"io_wqe_worker-%d/%d", index, wqe->node);
@ -783,21 +786,20 @@ struct io_cb_cancel_data {
static bool io_work_cancel(struct io_worker *worker, void *cancel_data)
{
struct io_cb_cancel_data *data = cancel_data;
struct io_wqe *wqe = data->wqe;
unsigned long flags;
bool ret = false;
/*
* Hold the lock to avoid ->cur_work going out of scope, caller
* may deference the passed in work.
* may dereference the passed in work.
*/
spin_lock_irqsave(&wqe->lock, flags);
spin_lock_irqsave(&worker->lock, flags);
if (worker->cur_work &&
data->cancel(worker->cur_work, data->caller_data)) {
send_sig(SIGINT, worker->task, 1);
ret = true;
}
spin_unlock_irqrestore(&wqe->lock, flags);
spin_unlock_irqrestore(&worker->lock, flags);
return ret;
}
@ -864,13 +866,20 @@ enum io_wq_cancel io_wq_cancel_cb(struct io_wq *wq, work_cancel_fn *cancel,
static bool io_wq_worker_cancel(struct io_worker *worker, void *data)
{
struct io_wq_work *work = data;
unsigned long flags;
bool ret = false;
if (worker->cur_work != work)
return false;
spin_lock_irqsave(&worker->lock, flags);
if (worker->cur_work == work) {
send_sig(SIGINT, worker->task, 1);
return true;
ret = true;
}
spin_unlock_irqrestore(&worker->lock, flags);
return false;
return ret;
}
static enum io_wq_cancel io_wqe_cancel_work(struct io_wqe *wqe,