Currently the iSCSI transport class synchronises target scanning and
unbinding with a host level mutex. For multi-session hosts (offloading
iSCSI HBAs) connecting to storage arrays that may implement one
target-per-lun, this can result in the target scan work for hundreds of
sessions being serialized behind a single mutex. With slow enough
response times, this can cause scan requests initiated from userspace to
block on the mutex long enough to trigger 120 sec hung task warnings.
I can't see any reason not to move this to a session level mutex and let
the target scans run in parallel, speeding up connecting to a large
number of targets. Note that as iscsi_tcp creates a virtual host for
each session, software iSCSI is effectively doing this already.
Signed-off-by: Chris Leech <cleech@xxxxxxxxxx>
---
drivers/scsi/scsi_transport_iscsi.c | 19 ++++++-------------
include/scsi/scsi_transport_iscsi.h | 2 +-
2 files changed, 7 insertions(+), 14 deletions(-)
diff --git a/drivers/scsi/scsi_transport_iscsi.c b/drivers/scsi/scsi_transport_iscsi.c
index 42bca61..83c90fa 100644
--- a/drivers/scsi/scsi_transport_iscsi.c
+++ b/drivers/scsi/scsi_transport_iscsi.c
@@ -1568,7 +1568,6 @@ static int iscsi_setup_host(struct transport_container *tc, struct device *dev,
memset(ihost, 0, sizeof(*ihost));
atomic_set(&ihost->nr_scans, 0);
- mutex_init(&ihost->mutex);
iscsi_bsg_host_add(shost, ihost);
/* ignore any bsg add error - we just can't do sgio */
@@ -1789,8 +1788,6 @@ static int iscsi_user_scan_session(struct device *dev, void *data)
{
struct iscsi_scan_data *scan_data = data;
struct iscsi_cls_session *session;
- struct Scsi_Host *shost;
- struct iscsi_cls_host *ihost;
unsigned long flags;
unsigned int id;
@@ -1801,10 +1798,7 @@ static int iscsi_user_scan_session(struct device *dev, void *data)
ISCSI_DBG_TRANS_SESSION(session, "Scanning session\n");
- shost = iscsi_session_to_shost(session);
- ihost = shost->shost_data;
-
- mutex_lock(&ihost->mutex);
+ mutex_lock(&session->mutex);
spin_lock_irqsave(&session->lock, flags);
if (session->state != ISCSI_SESSION_LOGGED_IN) {
spin_unlock_irqrestore(&session->lock, flags);
@@ -1823,7 +1817,7 @@ static int iscsi_user_scan_session(struct device *dev, void *data)
}
user_scan_exit:
- mutex_unlock(&ihost->mutex);
+ mutex_unlock(&session->mutex);
ISCSI_DBG_TRANS_SESSION(session, "Completed session scan\n");
return 0;
}
@@ -2001,26 +1995,24 @@ static void __iscsi_unbind_session(struct work_struct *work)
struct iscsi_cls_session *session =
container_of(work, struct iscsi_cls_session,
unbind_work);
- struct Scsi_Host *shost = iscsi_session_to_shost(session);
- struct iscsi_cls_host *ihost = shost->shost_data;
unsigned long flags;
unsigned int target_id;
ISCSI_DBG_TRANS_SESSION(session, "Unbinding session\n");
/* Prevent new scans and make sure scanning is not in progress */
- mutex_lock(&ihost->mutex);
+ mutex_lock(&session->mutex);
spin_lock_irqsave(&session->lock, flags);
if (session->target_id == ISCSI_MAX_TARGET) {
spin_unlock_irqrestore(&session->lock, flags);
- mutex_unlock(&ihost->mutex);
+ mutex_unlock(&session->mutex);
return;
}
target_id = session->target_id;
session->target_id = ISCSI_MAX_TARGET;
spin_unlock_irqrestore(&session->lock, flags);
- mutex_unlock(&ihost->mutex);
+ mutex_unlock(&session->mutex);
if (session->ida_used)
ida_simple_remove(&iscsi_sess_ida, target_id);
@@ -2053,6 +2045,7 @@ iscsi_alloc_session(struct Scsi_Host *shost, struct iscsi_transport *transport,
INIT_WORK(&session->unbind_work, __iscsi_unbind_session);
INIT_WORK(&session->scan_work, iscsi_scan_session);
spin_lock_init(&session->lock);
+ mutex_init(&session->mutex);
/* this is released in the dev's release function */
scsi_host_get(shost);
diff --git a/include/scsi/scsi_transport_iscsi.h b/include/scsi/scsi_transport_iscsi.h
index 6183d20..acf9d9d 100644
--- a/include/scsi/scsi_transport_iscsi.h
+++ b/include/scsi/scsi_transport_iscsi.h
@@ -238,6 +238,7 @@ struct iscsi_cls_session {
struct work_struct unblock_work;
struct work_struct scan_work;
struct work_struct unbind_work;
+ struct mutex mutex;
/* recovery fields */
int recovery_tmo;
@@ -272,7 +273,6 @@ struct iscsi_cls_session {
struct iscsi_cls_host {
atomic_t nr_scans;
- struct mutex mutex;
struct request_queue *bsg_q;
uint32_t port_speed;
uint32_t port_state;
--
2.7.4
--
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