Merge: dmaengine: idxd: Check availability of workqueue allocated by idxd wq driver before using

MR: https://gitlab.com/redhat/rhel/src/kernel/rhel-10/-/merge_requests/365

JIRA: https://issues.redhat.com/browse/RHEL-106609
CVE: CVE-2025-38369

This patch is a backport of the following upstream commit:
commit 17502e7
Author: Yi Sun <yi.sun@intel.com>
Date:   Fri May 9 08:03:04 2025 +0800

    dmaengine: idxd: Check availability of workqueue allocated by idxd wq driver before using

    Running IDXD workloads in a container with the /dev directory mounted can
    trigger a call trace or even a kernel panic when the parent process of the
    container is terminated.

    This issue occurs because, under certain configurations, Docker does not
    properly propagate the mount replica back to the original mount point.

    In this case, when the user driver detaches, the WQ is destroyed but it
    still calls destroy_workqueue() attempting to completes all pending work.
    It's necessary to check wq->wq and skip the drain if it no longer exists.

    Signed-off-by: Yi Sun <yi.sun@intel.com>
    Reviewed-by: Dave Jiang <dave.jiang@intel.com>
    Reviewed-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>

    Link: https://lore.kernel.org/r/20250509000304.1402863-1-yi.sun@intel.com
    Signed-off-by: Vinod Koul <vkoul@kernel.org>

Signed-off-by: Audra Mitchell <audra@redhat.com>

Approved-by: Jerry Snitselaar <jsnitsel@redhat.com>
Approved-by: Waiman Long <longman@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Jan Stancek <jstancek@redhat.com>

Author: jstancek

drivers/dma/idxd/cdev.c

@@ -349,7 +349,9 @@ static void idxd_cdev_evl_drain_pasid(struct idxd_wq *wq, u32 pasid)
 			set_bit(h, evl->bmap);
 		h = (h + 1) % size;
 	}
-	drain_workqueue(wq->wq);
+	if (wq->wq)
+		drain_workqueue(wq->wq);
+
 	mutex_unlock(&evl->lock);
 }