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Message-Id: <1285285052-16351-1-git-send-email-nab@linux-iscsi.org>
Date: Thu, 23 Sep 2010 16:37:32 -0700
From: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To: linux-scsi <linux-scsi@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Vasu Dev <vasu.dev@...ux.intel.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Andi Kleen <ak@...ux.intel.com>,
Matthew Wilcox <willy@...ux.intel.com>,
James Bottomley <James.Bottomley@...e.de>,
Mike Christie <michaelc@...wisc.edu>
Cc: James Smart <james.smart@...lex.com>,
Andrew Vasquez <andrew.vasquez@...gic.com>,
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
Hannes Reinecke <hare@...e.de>,
Joe Eykholt <jeykholt@...co.com>,
Christoph Hellwig <hch@....de>,
MPTFusionLinux <DL-MPTFusionLinux@....com>,
"eata.c maintainer" <dario.ballabio@...ind.it>,
Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: [RFC v3 01/15] scsi: Drop struct Scsi_Host->host_lock usage in scsi_dispatch_cmd()
From: Nicholas Bellinger <nab@...ux-iscsi.org>
This patch converts scsi_dispatch_cmd() drop the struct Scsi_Host->host_lock
legacy usage so that SHT->queuecommand() can be called without this lock held
softirq interrupts disabled via spin_lock_irq()
This patch drops the usage of scsi_cmd_get_serial() in scsi_dispatch_cmd()
and assumes the legacy SCSI LLDs that depend upon struct scsi_cmnd->serial_number
will call the now EXPORT_SYMBOL()'ed scsi_cmd_get_serial() call.
This patch also updates scsi_error.c:scsi_try_to_abort_cmd() to use:
if (test_bit(REQ_ATOM_COMPLETE, &scmd->request->atomic_flags))
return SUCCESS;
instead of checking for (scmd->serial_number == 0) following a recommendation
by Mike Christie.
This patch also converts the remaining struct Scsi_Host->cmd_serial_number to
atomic_t following a recommedation by Joe Eykholt 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.
Many thanks to Vasu Dev, Tim Chen, Mike and Joe for their help with particular
series!
Signed-off-by: Nicholas A. Bellinger <nab@...ux-iscsi.org>
---
drivers/scsi/scsi.c | 29 ++++++++++++++---------------
drivers/scsi/scsi_error.c | 10 +++++++---
include/scsi/scsi_cmnd.h | 1 +
include/scsi/scsi_host.h | 5 ++---
4 files changed, 24 insertions(+), 21 deletions(-)
diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index ad0ed21..84dbe76 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -628,18 +628,22 @@ void scsi_log_completion(struct scsi_cmnd *cmd, int disposition)
/**
* scsi_cmd_get_serial - Assign a serial number to a command
- * @host: the scsi host
* @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 LLDs that have a
+ * legacy requirement for struct scsi_cmnd->serial_number.
*/
-static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd *cmd)
+void scsi_cmd_get_serial(struct scsi_cmnd *cmd)
{
- cmd->serial_number = host->cmd_serial_number++;
- if (cmd->serial_number == 0)
- cmd->serial_number = host->cmd_serial_number++;
+ struct Scsi_Host *host = cmd->device->host;
+ /*
+ * 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.
@@ -651,7 +655,6 @@ static inline void scsi_cmd_get_serial(struct Scsi_Host *host, struct scsi_cmnd
int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
{
struct Scsi_Host *host = cmd->device->host;
- unsigned long flags = 0;
unsigned long timeout;
int rtn = 0;
@@ -736,15 +739,11 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
scsi_done(cmd);
goto out;
}
-
- spin_lock_irqsave(host->host_lock, flags);
/*
- * AK: unlikely race here: for some reason the timer could
- * expire before the serial number is set up below.
- *
- * TODO: kill serial or move to blk layer
+ * Note that scsi_cmd_get_serial() used to be called here, but
+ * now we expect the legacy SCSI LLDs that actually need this
+ * to call it directly within their SHT->queuecommand() caller.
*/
- scsi_cmd_get_serial(host, cmd);
if (unlikely(host->shost_state == SHOST_DEL)) {
cmd->result = (DID_NO_CONNECT << 16);
@@ -753,7 +752,7 @@ int scsi_dispatch_cmd(struct scsi_cmnd *cmd)
trace_scsi_dispatch_cmd_start(cmd);
rtn = host->hostt->queuecommand(cmd, scsi_done);
}
- spin_unlock_irqrestore(host->host_lock, flags);
+
if (rtn) {
trace_scsi_dispatch_cmd_error(cmd, rtn);
if (rtn != SCSI_MLQUEUE_DEVICE_BUSY &&
diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 1de30eb..34a4fce 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -39,6 +39,8 @@
#include "scsi_logging.h"
#include "scsi_transport_api.h"
+#include <../block/blk.h> /* For REQ_ATOM_COMPLETE */
+
#include <trace/events/scsi.h>
#define SENSE_TIMEOUT (10*HZ)
@@ -645,11 +647,13 @@ static int __scsi_try_to_abort_cmd(struct scsi_cmnd *scmd)
static int scsi_try_to_abort_cmd(struct scsi_cmnd *scmd)
{
/*
- * scsi_done was called just after the command timed out and before
- * we had a chance to process it. (db)
+ * Use the struct request atomic_flags here to check if
+ * block/blk.h:blk_mark_rq_complete() has already been called
+ * from the block softirq
*/
- if (scmd->serial_number == 0)
+ if (test_bit(REQ_ATOM_COMPLETE, &scmd->request->atomic_flags))
return SUCCESS;
+
return __scsi_try_to_abort_cmd(scmd);
}
diff --git a/include/scsi/scsi_cmnd.h b/include/scsi/scsi_cmnd.h
index a5e885a..bbba4fa 100644
--- a/include/scsi/scsi_cmnd.h
+++ b/include/scsi/scsi_cmnd.h
@@ -136,6 +136,7 @@ extern struct scsi_cmnd *__scsi_get_command(struct Scsi_Host *, gfp_t);
extern void scsi_put_command(struct scsi_cmnd *);
extern void __scsi_put_command(struct Scsi_Host *, struct scsi_cmnd *,
struct device *);
+extern void scsi_cmd_get_serial(struct scsi_cmnd *);
extern void scsi_finish_command(struct scsi_cmnd *cmd);
extern void *scsi_kmap_atomic_sg(struct scatterlist *sg, int sg_count,
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index b7bdecb..1b69511 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;
--
1.7.3
--
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