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.

Fixes: 05703271c3cd ("PCI/IOV: Add PCI rescan-remove locking when enabling/disabling SR-IOV")
Reported-by: Benjamin Block <bblock@linux.ibm.com>
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Benjamin Block <bblock@linux.ibm.com>
Acked-by: Gerd Bayer <gbayer@linux.ibm.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251216-revert_sriov_lock-v3-1-dac4925a7621@linux.ibm.com

diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
index 00784a60ba80bb55ff2790d8f87e15a90c652a24..7de5b18647beb69127ba11234fb9f1dec9b50540 100644 (file)
--- 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)