From b7f5a0bfe2061b2c7b2164de06fa4072d7373a45 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Mon, 15 Mar 2021 14:23:08 +0000
Subject: [PATCH] io_uring: fix sqpoll cancellation via task_work
Running sqpoll cancellations via task_work_run() is a bad idea because
it depends on other task works to be run, but those may be locked in
currently running task_work_run() because of how it's (splicing the list
in batches).
Enqueue and run them through a separate callback head, namely
struct io_sq_data::park_task_work. As a nice bonus we now precisely
control where it's run, that's much safer than guessing where it can
happen as it was before.
Reported-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/io_uring.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5c2de43b99f53f..5f4e312111ea73 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -274,6 +274,7 @@ struct io_sq_data {
unsigned long state;
struct completion exited;
+ struct callback_head *park_task_work;
};
#define IO_IOPOLL_BATCH 8
@@ -6727,6 +6728,7 @@ static int io_sq_thread(void *data)
cond_resched();
mutex_lock(&sqd->lock);
io_run_task_work();
+ io_run_task_work_head(&sqd->park_task_work);
timeout = jiffies + sqd->sq_thread_idle;
continue;
}
@@ -6781,6 +6783,7 @@ static int io_sq_thread(void *data)
}
finish_wait(&sqd->wait, &wait);
+ io_run_task_work_head(&sqd->park_task_work);
timeout = jiffies + sqd->sq_thread_idle;
}
@@ -6792,6 +6795,7 @@ static int io_sq_thread(void *data)
mutex_unlock(&sqd->lock);
io_run_task_work();
+ io_run_task_work_head(&sqd->park_task_work);
complete(&sqd->exited);
do_exit(0);
}
@@ -8890,7 +8894,7 @@ static void io_sqpoll_cancel_sync(struct io_ring_ctx *ctx)
if (task) {
init_completion(&work.completion);
init_task_work(&work.task_work, io_sqpoll_cancel_cb);
- WARN_ON_ONCE(task_work_add(task, &work.task_work, TWA_SIGNAL));
+ io_task_work_add_head(&sqd->park_task_work, &work.task_work);
wake_up_process(task);
}
io_sq_thread_unpark(sqd);
--
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