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authorJens Axboe <axboe@kernel.dk>2019-11-13 09:43:34 -0700
committerJens Axboe <axboe@kernel.dk>2019-11-13 13:51:54 -0700
commit36c2f9223e84c1aa84bfba90cb2e74b517c92a54 (patch)
treeacb3bcd8f5cb61020c13a32c6ef7cacea84dd167 /fs/io-wq.c
parent7d7230652e7c788ef908536fd79f4cca077f269f (diff)
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>
Diffstat (limited to 'fs/io-wq.c')
-rw-r--r--fs/io-wq.c47
1 files changed, 28 insertions, 19 deletions
diff --git a/fs/io-wq.c b/fs/io-wq.c
index 26d81540c1fc..4031b75541be 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -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
@@ -403,17 +404,6 @@ static void io_worker_handle_work(struct io_worker *worker)
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.
* Mark us stalled so we don't keep looking for work when we
@@ -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,