From adeaa3f290ecf7f6a6a5c53219a4686cbdff5fbd Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 13 Jun 2023 19:26:55 -0600
Subject: [PATCH] io_uring/io-wq: clear current->worker_private on exit
A recent fix stopped clearing PF_IO_WORKER from current->flags on exit,
which meant that we can now call inc/dec running on the worker after it
has been removed if it ends up scheduling in/out as part of exit.
If this happens after an RCU grace period has passed, then the struct
pointed to by current->worker_private may have been freed, and we can
now be accessing memory that is freed.
Ensure this doesn't happen by clearing the task worker_private field.
Both io_wq_worker_running() and io_wq_worker_sleeping() check this
field before going any further, and we don't need any accounting etc
done after this worker has exited.
Fixes: fd37b884003c ("io_uring/io-wq: don't clear PF_IO_WORKER on exit")
Reported-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
io_uring/io-wq.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
index fe38eb0cbc82a..399e9a15c38d6 100644
--- a/io_uring/io-wq.c
+++ b/io_uring/io-wq.c
@@ -220,7 +220,12 @@ static void io_worker_exit(struct io_worker *worker)
list_del_rcu(&worker->all_list);
raw_spin_unlock(&wq->lock);
io_wq_dec_running(worker);
- worker->flags = 0;
+ /*
+ * this worker is a goner, clear ->worker_private to avoid any
+ * inc/dec running calls that could happen as part of exit from
+ * touching 'worker'.
+ */
+ current->worker_private = NULL;
kfree_rcu(worker, rcu);
io_worker_ref_put(wq);
--
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