FAILED: patch "[PATCH] s390/pci: Prevent self deletion in disable_slot()" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 47c397844869ad0e6738afb5879c7492f4691122
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025062054-emotion-defiling-38ce@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 47c397844869ad0e6738afb5879c7492f4691122 Mon Sep 17 00:00:00 2001
From: Niklas Schnelle <[email protected]>
Date: Thu, 22 May 2025 14:13:13 +0200
Subject: [PATCH] s390/pci: Prevent self deletion in disable_slot()

As disable_slot() takes a struct zpci_dev from the Configured to the Standby state. In Standby there is still a hotplug slot so this is not usually a case of sysfs self deletion. This is important because self deletion gets very hairy in terms of locking (see for example recover_store() in arch/s390/pci/pci_sysfs.c).

Because the pci_dev_put() is not within the critical section of the zdev->state_lock however, disable_slot() can turn into a case of self deletion if zPCI device event handling slips between the mutex_unlock() and the pci_dev_put(). If the latter is the last put and zpci_release_device() is called this then tries to remove the hotplug slot via zpci_exit_slot() which will try to remove the hotplug slot directory the disable_slot() is part of i.e. self deletion.

Prevent this by widening the zdev->state_lock critical section to include the pci_dev_put() which is then guaranteed to happen with the struct zpci_dev still in Standby state ensuring it will not lead to a zpci_release_device() call as at least the zPCI event handling code still holds a reference.

index 055518ee354d..3d26d273f29d 100644
@@ -66,9 +66,9 @@ static int disable_slot(struct hotplug_slot *hotplug_slot)
 
 	rc = zpci_deconfigure_device(zdev);
 out:
-	mutex_unlock(&zdev->state_lock);
 	if (pdev)
 		pci_dev_put(pdev);
+	mutex_unlock(&zdev->state_lock);
 	return rc;
 }