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authorJens Axboe <axboe@kernel.dk>2021-03-05 08:44:39 -0700
committerJens Axboe <axboe@kernel.dk>2021-03-05 08:44:39 -0700
commit86e0d6766cf909813474857bd22fdc04c97c0b36 (patch)
tree7f4c0cd460986806724361175382efb35d7ced6b
parent09ca6c40c2024211657fdb2c50522a355610c3b7 (diff)
downloadlinux-stericsson-86e0d6766cf909813474857bd22fdc04c97c0b36.tar.gz
io_uring: make SQPOLL thread parking saner
We have this weird true/false return from parking, and then some of the callers decide to look at that. It can lead to unbalanced parks and sqd locking. Have the callers check the thread status once it's parked. We know we have the lock at that point, so it's either valid or it's NULL. Fix race with parking on thread exit. We need to be careful here with ordering of the sdq->lock and the IO_SQ_THREAD_SHOULD_PARK bit. Rename sqd->completion to sqd->parked to reflect that this is the only thing this completion event doesn. Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--fs/io_uring.c65
1 files changed, 30 insertions, 35 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5762750c666c..d30cbf0f7b1c 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -274,7 +274,7 @@ struct io_sq_data {
unsigned long state;
struct completion startup;
- struct completion completion;
+ struct completion parked;
struct completion exited;
};
@@ -6656,7 +6656,7 @@ static void io_sq_thread_parkme(struct io_sq_data *sqd)
* wait_task_inactive().
*/
preempt_disable();
- complete(&sqd->completion);
+ complete(&sqd->parked);
schedule_preempt_disabled();
preempt_enable();
}
@@ -6751,14 +6751,18 @@ static int io_sq_thread(void *data)
io_run_task_work();
- if (io_sq_thread_should_park(sqd))
- io_sq_thread_parkme(sqd);
-
/*
- * Clear thread under lock so that concurrent parks work correctly
+ * Ensure that we park properly if racing with someone trying to park
+ * while we're exiting. If we fail to grab the lock, check park and
+ * park if necessary. The ordering with the park bit and the lock
+ * ensures that we catch this reliably.
*/
- complete(&sqd->completion);
- mutex_lock(&sqd->lock);
+ if (!mutex_trylock(&sqd->lock)) {
+ if (io_sq_thread_should_park(sqd))
+ io_sq_thread_parkme(sqd);
+ mutex_lock(&sqd->lock);
+ }
+
sqd->thread = NULL;
list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
ctx->sqo_exec = 1;
@@ -7067,29 +7071,25 @@ static int io_sqe_files_unregister(struct io_ring_ctx *ctx)
static void io_sq_thread_unpark(struct io_sq_data *sqd)
__releases(&sqd->lock)
{
- if (!sqd->thread)
- return;
if (sqd->thread == current)
return;
clear_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
- wake_up_state(sqd->thread, TASK_PARKED);
+ if (sqd->thread)
+ wake_up_state(sqd->thread, TASK_PARKED);
mutex_unlock(&sqd->lock);
}
-static bool io_sq_thread_park(struct io_sq_data *sqd)
+static void io_sq_thread_park(struct io_sq_data *sqd)
__acquires(&sqd->lock)
{
if (sqd->thread == current)
- return true;
+ return;
+ set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
mutex_lock(&sqd->lock);
- if (!sqd->thread) {
- mutex_unlock(&sqd->lock);
- return false;
+ if (sqd->thread) {
+ wake_up_process(sqd->thread);
+ wait_for_completion(&sqd->parked);
}
- set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
- wake_up_process(sqd->thread);
- wait_for_completion(&sqd->completion);
- return true;
}
static void io_sq_thread_stop(struct io_sq_data *sqd)
@@ -7185,7 +7185,7 @@ static struct io_sq_data *io_get_sq_data(struct io_uring_params *p)
mutex_init(&sqd->lock);
init_waitqueue_head(&sqd->wait);
init_completion(&sqd->startup);
- init_completion(&sqd->completion);
+ init_completion(&sqd->parked);
init_completion(&sqd->exited);
return sqd;
}
@@ -7829,7 +7829,7 @@ static int io_sq_thread_fork(struct io_sq_data *sqd, struct io_ring_ctx *ctx)
int ret;
clear_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
- reinit_completion(&sqd->completion);
+ reinit_completion(&sqd->parked);
ctx->sqo_exec = 0;
sqd->task_pid = current->pid;
tsk = create_io_thread(io_sq_thread, sqd, NUMA_NO_NODE);
@@ -8712,7 +8712,6 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
struct files_struct *files)
{
struct task_struct *task = current;
- bool did_park = false;
if ((ctx->flags & IORING_SETUP_SQPOLL) && ctx->sq_data) {
/* never started, nothing to cancel */
@@ -8720,11 +8719,10 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
io_sq_offload_start(ctx);
return;
}
- did_park = io_sq_thread_park(ctx->sq_data);
- if (did_park) {
- task = ctx->sq_data->thread;
+ io_sq_thread_park(ctx->sq_data);
+ task = ctx->sq_data->thread;
+ if (task)
atomic_inc(&task->io_uring->in_idle);
- }
}
io_cancel_defer_files(ctx, task, files);
@@ -8733,10 +8731,10 @@ static void io_uring_cancel_task_requests(struct io_ring_ctx *ctx,
if (!files)
io_uring_try_cancel_requests(ctx, task, NULL);
- if (did_park) {
+ if (task)
atomic_dec(&task->io_uring->in_idle);
+ if (ctx->sq_data)
io_sq_thread_unpark(ctx->sq_data);
- }
}
/*
@@ -8836,15 +8834,12 @@ static void io_uring_cancel_sqpoll(struct io_ring_ctx *ctx)
if (!sqd)
return;
- if (!io_sq_thread_park(sqd))
- return;
- tctx = ctx->sq_data->thread->io_uring;
- /* can happen on fork/alloc failure, just ignore that state */
- if (!tctx) {
+ io_sq_thread_park(sqd);
+ if (!sqd->thread || !sqd->thread->io_uring) {
io_sq_thread_unpark(sqd);
return;
}
-
+ tctx = ctx->sq_data->thread->io_uring;
atomic_inc(&tctx->in_idle);
do {
/* read completions before cancelations */