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io_uring/io-wq: clear current->worker_private on exit

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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>
This commit is contained in:
Jens Axboe 2023-06-13 19:26:55 -06:00
parent cac9e4418f
commit adeaa3f290
1 changed files with 6 additions and 1 deletions
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7
io_uring/io-wq.c
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@ -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);