Re: [PATCH 5/6] qla2xxx: Prevent removal and board_disable race

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On Wed, 18 Jun 2014, Joe Lawrence wrote:

Introduce mutual exclusion between the qla2xxx_remove_one PCI driver
callback and qla2x00_disable_board_on_pci_error, which is scheduled as
board_disable work by qla2x00_check_reg{32,16}_for_disconnect:

* Leave the driver-specific data attached to the underlying PCI device
intact in qla2x00_disable_board_on_pci_error, so that qla2x00_remove_one
has enough breadcrumbs to determine that any board_disable work has been
completed.

* In qla2xxx_remove_one, set a bit to prevent any subsequent
board_disable work from scheduling, then cancel and wait until pending
work has completed.

* Reuse the PCI device enable count check in qla2x00_remove_one to
determine if board_disable has occured.  The original purpose of this
check was unnecessary since the driver remove function wasn't called
when the probe fails.

Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxxx>
---
drivers/scsi/qla2xxx/qla_def.h |    1 +
drivers/scsi/qla2xxx/qla_isr.c |    3 ++-
drivers/scsi/qla2xxx/qla_os.c  |   31 +++++++++++++++++++------------
3 files changed, 22 insertions(+), 13 deletions(-)

diff --git a/drivers/scsi/qla2xxx/qla_def.h b/drivers/scsi/qla2xxx/qla_def.h
index 1267b11..7c441c9 100644
--- a/drivers/scsi/qla2xxx/qla_def.h
+++ b/drivers/scsi/qla2xxx/qla_def.h
@@ -3404,6 +3404,7 @@ typedef struct scsi_qla_host {

	unsigned long	pci_flags;
#define PFLG_DISCONNECTED	0	/* PCI device removed */
+#define PFLG_DRIVER_REMOVING	1	/* PCI driver .remove */

	uint32_t	device_flags;
#define SWITCH_FOUND		BIT_0
diff --git a/drivers/scsi/qla2xxx/qla_isr.c b/drivers/scsi/qla2xxx/qla_isr.c
index 2741ad8..ee5eef4 100644
--- a/drivers/scsi/qla2xxx/qla_isr.c
+++ b/drivers/scsi/qla2xxx/qla_isr.c
@@ -117,7 +117,8 @@ qla2x00_check_reg32_for_disconnect(scsi_qla_host_t *vha, uint32_t reg)
{
	/* Check for PCI disconnection */
	if (reg == 0xffffffff) {
-		if (!test_and_set_bit(PFLG_DISCONNECTED, &vha->pci_flags)) {
+		if (!test_and_set_bit(PFLG_DISCONNECTED, &vha->pci_flags) &&
+		    !test_bit(PFLG_DRIVER_REMOVING, &vha->pci_flags)) {

In our remove function we set a bit that we are unloading:

set_bit (UNLOADING, &base_vha->dpc_flags);

could this be used instead?

			/*
			 * Schedule this (only once) on the default system
			 * workqueue so that all the adapter workqueues and the
diff --git a/drivers/scsi/qla2xxx/qla_os.c b/drivers/scsi/qla2xxx/qla_os.c
index 39c9953..51cba37 100644
--- a/drivers/scsi/qla2xxx/qla_os.c
+++ b/drivers/scsi/qla2xxx/qla_os.c
@@ -3123,15 +3123,25 @@ qla2x00_remove_one(struct pci_dev *pdev)
	scsi_qla_host_t *base_vha;
	struct qla_hw_data  *ha;

+	base_vha = pci_get_drvdata(pdev);
+	ha = base_vha->hw;
+
+	/* Indicate device removal to prevent future board_disable and wait
+	 * until any pending board_disable has completed. */
+	set_bit(PFLG_DRIVER_REMOVING, &base_vha->pci_flags);
+	cancel_work_sync(&ha->board_disable);
+
	/*
-	 * If the PCI device is disabled that means that probe failed and any
-	 * resources should be have cleaned up on probe exit.
+	 * If the PCI device is disabled then there was a PCI-disconnect and
+	 * qla2x00_disable_board_on_pci_error has taken care of most of the
+	 * resources.
	 */
-	if (!atomic_read(&pdev->enable_cnt))
+	if (!atomic_read(&pdev->enable_cnt)) {

Should we also add a check here that this is a disconnection before freeing these structs? The original intent of the check for pdev->enable_cnt is to make sure we don't try to dereference an already freed struct if probe failed.

+		scsi_host_put(base_vha->host);
+		kfree(ha);
+		pci_set_drvdata(pdev, NULL);
		return;
-
-	base_vha = pci_get_drvdata(pdev);
-	ha = base_vha->hw;
+	}

	qla2x00_wait_for_hba_ready(base_vha);

@@ -4791,18 +4801,15 @@ qla2x00_disable_board_on_pci_error(struct work_struct *work)
	qla82xx_md_free(base_vha);
	qla2x00_free_queues(ha);

-	scsi_host_put(base_vha->host);
-
	qla2x00_unmap_iobases(ha);

	pci_release_selected_regions(ha->pdev, ha->bars);
-	kfree(ha);
-	ha = NULL;
-
	pci_disable_pcie_error_reporting(pdev);
	pci_disable_device(pdev);
-	pci_set_drvdata(pdev, NULL);

+	/*
+	 * Let qla2x00_remove_one cleanup qla_hw_data on device removal.
+	 */
}

/**************************************************************************

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