linux-kernel - [PATCH v3 1/2] Revert "PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV"

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Message-Id: <20251216-revert_sriov_lock-v3-1-dac4925a7621@linux.ibm.com>
Date: Tue, 16 Dec 2025 23:14:02 +0100
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Lukas Wunner <lukas@...ner.de>, Keith Busch <kbusch@...nel.org>,
        Gerd Bayer <gbayer@...ux.ibm.com>,
        Matthew Rosato <mjrosato@...ux.ibm.com>,
        Benjamin Block <bblock@...ux.ibm.com>,
        Halil Pasic <pasic@...ux.ibm.com>, Farhan Ali <alifm@...ux.ibm.com>,
        Julian Ruess <julianr@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Niklas Schnelle <schnelle@...ux.ibm.com>
Subject: [PATCH v3 1/2] Revert "PCI/IOV: Add PCI rescan-remove locking when
 enabling/disabling SR-IOV"

This reverts commit 05703271c3cd ("PCI/IOV: Add PCI rescan-remove
locking when enabling/disabling SR-IOV") which causes a deadlock by
recursively taking pci_rescan_remove_lock when sriov_del_vfs() is called
as part of pci_stop_and_remove_bus_device(). For example with the
following sequence of commands:

$ echo <NUM> > /sys/bus/pci/devices/<pf>/sriov_numvfs
$ echo 1 > /sys/bus/pci/devices/<pf>/remove

A trimmed trace of the deadlock on a mlx5 device is as below:

    zsh/5715 is trying to acquire lock:
    000002597926ef50 (pci_rescan_remove_lock){+.+.}-{3:3}, at: sriov_disable+0x34/0x140

    but task is already holding lock:
    000002597926ef50 (pci_rescan_remove_lock){+.+.}-{3:3}, at: pci_stop_and_remove_bus_device_locked+0x24/0x80
    ...
    Call Trace:
     [<00000259778c4f90>] dump_stack_lvl+0xc0/0x110
     [<00000259779c844e>] print_deadlock_bug+0x31e/0x330
     [<00000259779c1908>] __lock_acquire+0x16c8/0x32f0
     [<00000259779bffac>] lock_acquire+0x14c/0x350
     [<00000259789643a6>] __mutex_lock_common+0xe6/0x1520
     [<000002597896413c>] mutex_lock_nested+0x3c/0x50
     [<00000259784a07e4>] sriov_disable+0x34/0x140
     [<00000258f7d6dd80>] mlx5_sriov_disable+0x50/0x80 [mlx5_core]
     [<00000258f7d5745e>] remove_one+0x5e/0xf0 [mlx5_core]
     [<00000259784857fc>] pci_device_remove+0x3c/0xa0
     [<000002597851012e>] device_release_driver_internal+0x18e/0x280
     [<000002597847ae22>] pci_stop_bus_device+0x82/0xa0
     [<000002597847afce>] pci_stop_and_remove_bus_device_locked+0x5e/0x80
     [<00000259784972c2>] remove_store+0x72/0x90
     [<0000025977e6661a>] kernfs_fop_write_iter+0x15a/0x200
     [<0000025977d7241c>] vfs_write+0x24c/0x300
     [<0000025977d72696>] ksys_write+0x86/0x110
     [<000002597895b61c>] __do_syscall+0x14c/0x400
     [<000002597896e0ee>] system_call+0x6e/0x90

This alone is not a complete fix as it restores the issue the cited
commit tried to solve. A new fix will be provided as a follow on.

Cc: stable@...r.kernel.org
Fixes: 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV")
Reported-by: Benjamin Block <bblock@...ux.ibm.com>
Reviewed-by: Benjamin Block <bblock@...ux.ibm.com>
Acked-by: Gerd Bayer <gbayer@...ux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
---
 drivers/pci/iov.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 00784a60ba80bb55ff2790d8f87e15a90c652a24..7de5b18647beb69127ba11234fb9f1dec9b50540 100644
--- a/drivers/pci/iov.c
+++ b/drivers/pci/iov.c
@@ -629,18 +629,15 @@ static int sriov_add_vfs(struct pci_dev *dev, u16 num_vfs)
 	if (dev->no_vf_scan)
 		return 0;
 
-	pci_lock_rescan_remove();
 	for (i = 0; i < num_vfs; i++) {
 		rc = pci_iov_add_virtfn(dev, i);
 		if (rc)
 			goto failed;
 	}
-	pci_unlock_rescan_remove();
 	return 0;
 failed:
 	while (i--)
 		pci_iov_remove_virtfn(dev, i);
-	pci_unlock_rescan_remove();
 
 	return rc;
 }
@@ -765,10 +762,8 @@ static void sriov_del_vfs(struct pci_dev *dev)
 	struct pci_sriov *iov = dev->sriov;
 	int i;
 
-	pci_lock_rescan_remove();
 	for (i = 0; i < iov->num_VFs; i++)
 		pci_iov_remove_virtfn(dev, i);
-	pci_unlock_rescan_remove();
 }
 
 static void sriov_disable(struct pci_dev *dev)

-- 
2.51.0