PCI: Rework config space blocking services

pci_block_user_cfg_access was designed for the use case that a single
context, the IPR driver, temporarily delays user space accesses to the
config space via sysfs. This assumption became invalid by the time
pci_dev_reset was added as locking instance. Today, if you run two loops
in parallel that reset the same device via sysfs, you end up with a
kernel BUG as pci_block_user_cfg_access detect the broken assumption.

This reworks the pci_block_user_cfg_access to a sleeping service
pci_cfg_access_lock and an atomic-compatible variant called
pci_cfg_access_trylock. The former not only blocks user space access as
before but also waits if access was already locked. The latter service
just returns false in this case, allowing the caller to resolve the
conflict instead of raising a BUG.

Adaptions of the ipr driver were originally written by Brian King.

Acked-by: Brian King <brking@linux.vnet.ibm.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/uio/uio_pci_generic.c b/drivers/uio/uio_pci_generic.c
index 02bd47bdee1..56d00c6258f 100644
--- a/drivers/uio/uio_pci_generic.c
+++ b/drivers/uio/uio_pci_generic.c
@@ -55,7 +55,8 @@ static irqreturn_t irqhandler(int irq, struct uio_info *info)
 	BUILD_BUG_ON(PCI_COMMAND % 4);
 	BUILD_BUG_ON(PCI_COMMAND + 2 != PCI_STATUS);
 
-	pci_block_user_cfg_access(pdev);
+	if (!pci_cfg_access_trylock(pdev))
+		goto error;
 
 	/* Read both command and status registers in a single 32-bit operation.
 	 * Note: we could cache the value for command and move the status read
@@ -79,7 +80,7 @@ static irqreturn_t irqhandler(int irq, struct uio_info *info)
 	ret = IRQ_HANDLED;
 done:
 
-	pci_unblock_user_cfg_access(pdev);
+	pci_cfg_access_lock(pdev);
 	return ret;
 }
 
@@ -91,7 +92,7 @@ static int __devinit verify_pci_2_3(struct pci_dev *pdev)
 	u16 orig, new;
 	int err = 0;
 
-	pci_block_user_cfg_access(pdev);
+	pci_cfg_access_lock(pdev);
 	pci_read_config_word(pdev, PCI_COMMAND, &orig);
 	pci_write_config_word(pdev, PCI_COMMAND,
 			      orig ^ PCI_COMMAND_INTX_DISABLE);
@@ -114,7 +115,7 @@ static int __devinit verify_pci_2_3(struct pci_dev *pdev)
 	/* Now restore the original value. */
 	pci_write_config_word(pdev, PCI_COMMAND, orig);
 err:
-	pci_unblock_user_cfg_access(pdev);
+	pci_cfg_access_unlock(pdev);
 	return err;
 }