Re: [PATCH 2/2]: PCI Error Recovery: Symbios SCSI First Failure

Matthew Wilcox
2007-10-01T20:12:47Z

On Thu, Sep 27, 2007 at 06:34:37PM -0500, Linas Vepstas wrote:
> Good catch. But no ... and I had to study this a bit. Bear with me:

I agree with the analysis which I've now snipped.

> I think the race you describe above is harmless. The first time
> that sym_eh_handler() will run, it will be with SYM_EH_ABORT,
> in it doesn't matter if we lose that, since the device is hosed
> anyway. At some later time, it will run with SYM_EH_DEVICE_RESET
> and then SYM_EH_BUS_RESET and then SYM_EH_HOST_RESET, and we won't
> miss those, since, by now, sym2_io_error_detected() will have run.
>
> So, by my reading, I'd say that init_completion() in
> sym2_io_error_detected() has to stay (although perhaps
> it should be replaced by the INIT_COMPLETION() macro.)
> Removing it will prevent correct operation on the second
> and subsequent errors.

I think the fundamental problem is that completions aren't really
supposed to be used like this. Here's one attempt at using completions
perhaps a little more the way they're supposed to be used, although now
I've written it, I wonder if we shouldn't just use a waitqueue instead.

diff --git a/drivers/scsi/sym53c8xx_2/sym_glue.c b/drivers/scsi/sym53c8xx_2/sym_glue.c
index e8a4361..b425b89 100644
--- a/drivers/scsi/sym53c8xx_2/sym_glue.c
+++ b/drivers/scsi/sym53c8xx_2/sym_glue.c
@@ -602,6 +602,7 @@ static int sym_eh_handler(int op, char *opname, struct scsi_cmnd *cmd)
struct sym_hcb *np = SYM_SOFTC_PTR(cmd);
struct sym_ucmd *ucmd = SYM_UCMD_PTR(cmd);
struct Scsi_Host *host = cmd->device->host;
+ struct pci_dev *pdev = np->s.device;
SYM_QUEHEAD *qp;
int cmd_queued = 0;
int sts = -1;
@@ -616,9 +617,19 @@ static int sym_eh_handler(int op, char *opname, struct scsi_cmnd *cmd)
* point in hurrying; take a leisurely wait.
*/
#define WAIT_FOR_PCI_RECOVERY 35
- if (pci_channel_offline(np->s.device)) {
- int finished_reset = wait_for_completion_timeout(
- &np->s.io_reset_wait, WAIT_FOR_PCI_RECOVERY*HZ);
+ if (pci_channel_offline(pdev)) {
+ struct host_data *hostdata = shost_priv(host);
+ int finished_reset = 0;
+ init_completion(&eh_done);
+ spin_lock_irq(host->host_lock);
+ if (!hostdata->io_reset)
+ hostdata->io_reset = &eh_done;
+ if (!pci_channel_offline(pdev))
+ finished_reset = 1;
+ spin_unlock_irq(host->host_lock);
+ if (!finished_reset)
+ finished_reset = wait_for_completion_timeout(
+ hostdata->io_reset, WAIT_FOR_PCI_RECOVERY*HZ);
if (!finished_reset)
return SCSI_FAILED;
}
@@ -1396,7 +1407,6 @@ static struct Scsi_Host * __devinit sym_attach(struct scsi_host_template *tpnt,
np->maxoffs = dev->chip.offset_max;
np->maxburst = dev->chip.burst_max;
np->myaddr = dev->host_id;
- init_completion(&np->s.io_reset_wait);

/*
* Edit its name.
@@ -1842,15 +1852,12 @@ static void __devexit sym2_remove(struct pci_dev *pdev)
static pci_ers_result_t sym2_io_error_detected(struct pci_dev *pdev,
enum pci_channel_state state)
{
- struct sym_hcb *np = pci_get_drvdata(pdev);
-
/* If slot is permanently frozen, turn everything off */
if (state == pci_channel_io_perm_failure) {
sym2_remove(pdev);
return PCI_ERS_RESULT_DISCONNECT;
}

- init_completion(&np->s.io_reset_wait);
disable_irq(pdev->irq);
pci_disable_device(pdev);

@@ -1912,7 +1919,7 @@ static pci_ers_result_t sym2_io_slot_reset(struct pci_dev *pdev)
sym_name(np));

if (pci_enable_device(pdev)) {
- printk(KERN_ERR "%s: Unable to enable afer PCI reset\n",
+ printk(KERN_ERR "%s: Unable to enable after PCI reset\n",
sym_name(np));
return PCI_ERS_RESULT_DISCONNECT;
}
@@ -1953,7 +1960,14 @@ static pci_ers_result_t sym2_io_slot_reset(struct pci_dev *pdev)
static void sym2_io_resume(struct pci_dev *pdev)
{
struct sym_hcb *np = pci_get_drvdata(pdev);
- complete_all(&np->s.io_reset_wait);
+ struct Scsi_Host *shost = np->s.host;
+ struct host_data *hostdata = shost_priv(shost);
+
+ spin_lock_irq(shost->host_lock);
+ if (hostdata->io_reset)
+ complete_all(hostdata->io_reset);
+ hostdata->io_reset = NULL;
+ spin_unlock_irq(shost->host_lock);
}

static void sym2_get_signalling(struct Scsi_Host *shost)
diff --git a/drivers/scsi/sym53c8xx_2/sym_glue.h b/drivers/scsi/sym53c8xx_2/sym_glue.h
index a172cc5..b961f70 100644
--- a/drivers/scsi/sym53c8xx_2/sym_glue.h
+++ b/drivers/scsi/sym53c8xx_2/sym_glue.h
@@ -180,9 +180,6 @@ struct sym_shcb {
char chip_name[8];
struct pci_dev *device;

- /* Waiter for clearing of frozen PCI bus */
- struct completion io_reset_wait;
-
struct Scsi_Host *host;

void __iomem * ioaddr; /* MMIO kernel io address */
@@ -223,6 +220,7 @@ struct sym_device {
*/
struct host_data {
struct sym_hcb *ncb;
+ struct completion *io_reset; /* PCI error handling */
};

static inline struct sym_hcb * sym_get_hcb(struct Scsi_Host *host)

--
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operating system, but compare it to ours. We can't possibly take such
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