CVE-2026-74574: dmaengine: idxd: fix fdev setup failure cleanup in idxd_cdev_open()

In the Linux kernel, the following vulnerability has been resolved:

dmaengine: idxd: fix fdev setup failure cleanup in idxdcdevopen()

The faileddevadd and faileddevname paths drop the file-device reference while wq->wqlock is still held. If putdevice(fdev) drops the last reference, idxdfiledevrelease() runs synchronously and tries to take wq->wqlock again, deadlocking.

Those paths also fall through into the later ctx cleanup labels even though idxdfiledevrelease() owns that cleanup and frees ctx. This can make idxdxapasidremove(ctx) and kfree(ctx) operate on a freed context.

Move idxdwqget() before file-device setup can fail, since the release callback always calls idxdwqput(). Then unlock wq->wqlock before putdevice(fdev) and return directly from the file-device setup failure path, leaving ctx cleanup to the release callback.