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There is an acct->nr_worker visit without lock protection. Think about
the case: two callers call io_wqe_wake_worker(), one is the original
context and the other one is an io-worker(by calling
io_wqe_enqueue(wqe, linked)), on two cpus paralelly, this may cause
nr_worker to be larger than max_worker.
Let's fix it by adding lock for it, and let's do nr_workers++ before
create_io_worker. There may be a edge cause that the first caller fails
to create an io-worker, but the second caller doesn't know it and then
quit creating io-worker as well:
say nr_worker = max_worker - 1
cpu 0 cpu 1
io_wqe_wake_worker() io_wqe_wake_worker()
nr_worker < max_worker
nr_worker++
create_io_worker() nr_worker == max_worker
failed return
return
But the chance of this case is very slim.
Fixes: 685fe7feedb9 ("io-wq: eliminate the need for a manager thread")
Signed-off-by: Hao Xu <haoxu@linux.alibaba.com>
[axboe: fix unconditional create_io_worker() call]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
3d4e4face9