FAILED: patch "[PATCH] PCI: endpoint: Avoid creating sub-groups asynchronously" failed to apply to 5.15-stable tree

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

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 7c5c7d06bd1f86d2c3ebe62be903a4ba42db4d2c
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026021309-browse-cloud-99d5@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:



thanks,

greg k-h

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

From 7c5c7d06bd1f86d2c3ebe62be903a4ba42db4d2c Mon Sep 17 00:00:00 2001
From: Liu Song <liu.song13@zte.com.cn>
Date: Thu, 10 Jul 2025 14:38:45 +0800
Subject: [PATCH] PCI: endpoint: Avoid creating sub-groups asynchronously

The asynchronous creation of sub-groups by a delayed work could lead to a
NULL pointer dereference when the driver directory is removed before the
work completes.

The crash can be easily reproduced with the following commands:

  # cd /sys/kernel/config/pci_ep/functions/pci_epf_test
  # for i in {1..20}; do mkdir test && rmdir test; done

  BUG: kernel NULL pointer dereference, address: 0000000000000088
  ...
  Call Trace:
   configfs_register_group+0x3d/0x190
   pci_epf_cfs_work+0x41/0x110
   process_one_work+0x18f/0x350
   worker_thread+0x25a/0x3a0

Fix this issue by using configfs_add_default_group() API which does not
have the deadlock problem as configfs_register_group() and does not require
the delayed work handler.

Fixes: e85a2d783762 ("PCI: endpoint: Add support in configfs to associate two EPCs with EPF")
Signed-off-by: Liu Song <liu.song13@zte.com.cn>
[mani: slightly reworded the description and added stable list]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@kernel.org
Link: https://patch.msgid.link/20250710143845409gLM6JdlwPhlHG9iX3F6jK@zte.com.cn

diff --git a/drivers/pci/endpoint/pci-ep-cfs.c b/drivers/pci/endpoint/pci-ep-cfs.c
index ef50c82e647f..43feb6139fa3 100644
--- a/drivers/pci/endpoint/pci-ep-cfs.c
+++ b/drivers/pci/endpoint/pci-ep-cfs.c
@@ -23,7 +23,6 @@ struct pci_epf_group {
 	struct config_group group;
 	struct config_group primary_epc_group;
 	struct config_group secondary_epc_group;
-	struct delayed_work cfs_work;
 	struct pci_epf *epf;
 	int index;
 };
@@ -103,7 +102,7 @@ static struct config_group
 	secondary_epc_group = &epf_group->secondary_epc_group;
 	config_group_init_type_name(secondary_epc_group, "secondary",
 				    &pci_secondary_epc_type);
-	configfs_register_group(&epf_group->group, secondary_epc_group);
+	configfs_add_default_group(secondary_epc_group, &epf_group->group);
 
 	return secondary_epc_group;
 }
@@ -166,7 +165,7 @@ static struct config_group
 
 	config_group_init_type_name(primary_epc_group, "primary",
 				    &pci_primary_epc_type);
-	configfs_register_group(&epf_group->group, primary_epc_group);
+	configfs_add_default_group(primary_epc_group, &epf_group->group);
 
 	return primary_epc_group;
 }
@@ -570,15 +569,13 @@ static void pci_ep_cfs_add_type_group(struct pci_epf_group *epf_group)
 		return;
 	}
 
-	configfs_register_group(&epf_group->group, group);
+	configfs_add_default_group(group, &epf_group->group);
 }
 
-static void pci_epf_cfs_work(struct work_struct *work)
+static void pci_epf_cfs_add_sub_groups(struct pci_epf_group *epf_group)
 {
-	struct pci_epf_group *epf_group;
 	struct config_group *group;
 
-	epf_group = container_of(work, struct pci_epf_group, cfs_work.work);
 	group = pci_ep_cfs_add_primary_group(epf_group);
 	if (IS_ERR(group)) {
 		pr_err("failed to create 'primary' EPC interface\n");
@@ -637,9 +634,7 @@ static struct config_group *pci_epf_make(struct config_group *group,
 
 	kfree(epf_name);
 
-	INIT_DELAYED_WORK(&epf_group->cfs_work, pci_epf_cfs_work);
-	queue_delayed_work(system_wq, &epf_group->cfs_work,
-			   msecs_to_jiffies(1));
+	pci_epf_cfs_add_sub_groups(epf_group);
 
 	return &epf_group->group;