[PATCH] scsi: Convert scsi_host->cmd_serial_number to odd numbered atomic_t counter

Nicholas A. Bellinger
2010-11-11T10:46:50Z

From: Nicholas Bellinger <nab@linux-iscsi.org>

This patch converts struct scsi_host->cmd_serial_number to a 'odd incremented by 2'
atomic_t counter in scsi_cmd_get_serial(), and moves the host_lock held call in
jgarzik's DEF_SCSI_QCMD() wrapper back into it's original location in scsi_dispatch_cmd().

Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
---
drivers/scsi/hosts.c | 1 +
drivers/scsi/scsi.c | 20 ++++++++++++++------
include/scsi/scsi_host.h | 7 ++-----
3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 4f7a582..317af8e 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -381,6 +381,7 @@ struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
shost->unchecked_isa_dma = sht->unchecked_isa_dma;
shost->use_clustering = sht->use_clustering;
shost->ordered_tag = sht->ordered_tag;
+ atomic_set(&shost->cmd_serial_number, 1);

if (sht->supported_mode == MODE_UNKNOWN)
/* means we didn't set it ... default to INITIATOR */
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index e3d0629..bdc0837 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -632,15 +632,17 @@ void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
* @cmd: command to assign serial number to
*
* Description: a serial number identifies a request for error recovery
- * and debugging purposes. Protected by the Host_Lock of host.
+ * and debugging purposes. Called directly by scsi_dispatch_cmd() for all LLDs
+ * after the great host_lock pushdown.
*/
-void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)
+static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)
{
- cmd->serial_number = host->cmd_serial_number++;
- if (cmd->serial_number == 0)
- cmd->serial_number = host->cmd_serial_number++;
+ /*
+ * Increment the host->cmd_serial_number by 2 so cmd->serial_number
+ * is always odd and wraps to 1 instead of 0.
+ */
+ cmd->serial_number = atomic_add_return(2, &host->cmd_serial_number);
}
-EXPORT_SYMBOL(scsi_cmd_get_serial);

/**
* scsi_dispatch_command - Dispatch a command to the low-level driver.
@@ -736,6 +738,12 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
scsi_done(cmd);
goto out;
}
+ /*
+ * Assign a cmd->serial_number from host->cmd_serial_number that
+ * is used by scsi_softirq_done() to signal scsi_try_to_abort_cmd()
+ * that a outstanding cmd has been completed.
+ */
+ scsi_cmd_get_serial(host, cmd);

if (unlikely(host->shost_state == SHOST_DEL)) {
cmd->result = (DID_NO_CONNECT << 16);
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index cea74ba..6909038 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -518,7 +518,6 @@ struct scsi_host_template {
int rc; \
struct Scsi_Host *shost = cmd->device->host; \
spin_lock_irqsave(shost->host_lock, irq_flags); \
- scsi_cmd_get_serial(shost, cmd); \
rc = func_name##_lck (cmd, done); \
spin_unlock_irqrestore(shost->host_lock, irq_flags); \
return rc; \
@@ -625,10 +624,9 @@ struct Scsi_Host {
short unsigned int max_sectors;
unsigned long dma_boundary;
/*
- * Used to assign serial numbers to the cmds.
- * Protected by the host lock.
+ * Used to assign serial numbers to the cmds in scsi_cmd_get_serial()
*/
- unsigned long cmd_serial_number;
+ atomic_t cmd_serial_number;

unsigned active_mode:2;
unsigned unchecked_isa_dma:1;
@@ -773,7 +771,6 @@ extern struct Scsi_Host *scsi_host_get(struct Scsi_Host *);
extern void scsi_host_put(struct Scsi_Host *t);
extern struct Scsi_Host *scsi_host_lookup(unsigned short);
extern const char *scsi_host_state_name(enum scsi_host_state);
-extern void scsi_cmd_get_serial(struct Scsi_Host *, struct scsi_cmnd *);

extern u64 scsi_calculate_bounce_limit(struct Scsi_Host *);

--
1.5.6.5