From: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx>
This patch converts struct Scsi_Host->cmd_serial_number to an atomic_t so that
scsi_cmd_get_serial() can be safely called without struct Scsi_Host->host_lock
in scsi_dispatch_cmd(). This patch also adds a struct Scsi_Host->use_serial_number
to signal serial_number usage, but this is now disabled by default in
scsi_host_alloc().
One special item in scsi_cmd_get_serial() recommended by Joe Eykholt is to
start struct Scsi_Host->cmd_serial_number at 1, and increment each serial_number
by 2 so that the serial is odd, and wraps to 1 instead of 0.
Signed-off-by: Nicholas A. Bellinger <nab@xxxxxxxxxxxxxxx>
---
drivers/scsi/hosts.c | 4 ++++
drivers/scsi/scsi.c | 13 ++++++++++---
include/scsi/scsi_host.h | 8 +++++---
3 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 8a8f803..aff1c9c 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -380,6 +380,10 @@ 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;
+ /*
+ * Set the default shost->cmd_serial_number to 1.
+ */
+ 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 ad0ed21..4724ce7 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -636,9 +636,16 @@ void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
*/
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++;
+ /*
+ * The use of per struct scsi_cmnd->serial_number is disabled by default
+ */
+ if (!(host->use_serial_number))
+ return;
+ /*
+ * 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);
}
/**
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index b7bdecb..b08d0f2 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -602,10 +602,9 @@ 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;
@@ -636,6 +635,9 @@ struct Scsi_Host {
/* Asynchronous scan in progress */
unsigned async_scan:1;
+ /* Signal usage of per struct scsi_cmnd->serial_number */
+ unsigned use_serial_number:1;
+
/*
* Optional work queue to be utilized by the transport
*/
--
1.7.2.3
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