FAILED: patch "[PATCH] s390/pci: Serialize device addition and removal" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 774a1fa880bc949d88b5ddec9494a13be733dfa8
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025062020-oxygen-print-635f@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 774a1fa880bc949d88b5ddec9494a13be733dfa8 Mon Sep 17 00:00:00 2001
From: Niklas Schnelle <[email protected]>
Date: Thu, 22 May 2025 14:13:15 +0200
Subject: [PATCH] s390/pci: Serialize device addition and removal

Prior changes ensured that when zpci_release_device() is called and it removed the zdev from the zpci_list this instance can not be found via the zpci_list anymore even while allowing re-add of reserved devices. This only accounts for the overall lifetime and zpci_list addition and removal, it does not yet prevent concurrent add of a new instance for the same underlying device. Such concurrent add would subsequently cause issues such as attempted re-use of the same IOMMU sysfs directory and is generally undesired.

Introduce a new zpci_add_remove_lock mutex to serialize adding a new device with removal. Together this ensures that if a struct zpci_dev is not found in the zpci_list it was either already removed and torn down, or its removal and tear down is in progress with the zpci_add_remove_lock held.

index 4602abd0c6f1..cd6676c2d602 100644
@@ -45,6 +45,7 @@
 /* list of all detected zpci devices */
 static LIST_HEAD(zpci_list);
 static DEFINE_SPINLOCK(zpci_list_lock);
+static DEFINE_MUTEX(zpci_add_remove_lock);
 
 static DECLARE_BITMAP(zpci_domain, ZPCI_DOMAIN_BITMAP_SIZE);
 static DEFINE_SPINLOCK(zpci_domain_lock);

@@ -74,7 +75,9 @@ void zpci_zdev_put(struct zpci_dev *zdev)
 {
 	if (!zdev)
 		return;
+	mutex_lock(&zpci_add_remove_lock);
 	kref_put_lock(&zdev->kref, zpci_release_device, &zpci_list_lock);
+	mutex_unlock(&zpci_add_remove_lock);
 }
 
 struct zpci_dev *get_zdev_by_fid(u32 fid)

@@ -844,6 +847,7 @@ int zpci_add_device(struct zpci_dev *zdev)
 {
 	int rc;
 
+	mutex_lock(&zpci_add_remove_lock);
 	zpci_dbg(1, "add fid:%x, fh:%x, c:%d\n", zdev->fid, zdev->fh, zdev->state);
 	rc = zpci_init_iommu(zdev);
 	if (rc)

@@ -857,12 +861,14 @@ int zpci_add_device(struct zpci_dev *zdev)
 	spin_lock(&zpci_list_lock);
 	list_add_tail(&zdev->entry, &zpci_list);
 	spin_unlock(&zpci_list_lock);
+	mutex_unlock(&zpci_add_remove_lock);
 	return 0;
 
 error_destroy_iommu:
 	zpci_destroy_iommu(zdev);
 error:
 	zpci_dbg(0, "add fid:%x, rc:%d\n", zdev->fid, rc);
+	mutex_unlock(&zpci_add_remove_lock);
 	return rc;
 }
 

@@ -953,6 +959,7 @@ void zpci_release_device(struct kref *kref)
 {
 	struct zpci_dev *zdev = container_of(kref, struct zpci_dev, kref);
 
+	lockdep_assert_held(&zpci_add_remove_lock);
 	WARN_ON(zdev->state != ZPCI_FN_STATE_RESERVED);
 	/*
 	 * We already hold zpci_list_lock thanks to kref_put_lock().