[PATCH 3.12 055/142] target: Fix COMPARE_AND_WRITE with SG_TO_MEM_NOALLOC handling

Jiri Slaby
2015-05-16T08:19:10Z

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

3.12-stable review patch. If anyone has any objections, please let me know.

===============

commit c8e639852ad720499912acedfd6b072325fd2807 upstream.

This patch fixes a bug for COMPARE_AND_WRITE handling with
fabrics using SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC.

It adds the missing allocation for cmd->t_bidi_data_sg within
transport_generic_new_cmd() that is used by COMPARE_AND_WRITE
for the initial READ payload, even if the fabric is already
providing a pre-allocated buffer for cmd->t_data_sg.

Also, fix zero-length COMPARE_AND_WRITE handling within the
compare_and_write_callback() and target_complete_ok_work()
to queue the response, skipping the initial READ.

This fixes COMPARE_AND_WRITE emulation with loopback, vhost,
and xen-backend fabric drivers using SG_TO_MEM_NOALLOC.

Reported-by: Christoph Hellwig <hch@lst.de>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
drivers/target/target_core_sbc.c | 15 +++++++++-----
drivers/target/target_core_transport.c | 37 ++++++++++++++++++++++++++++++----
include/target/target_core_base.h | 2 +-
3 files changed, 44 insertions(+), 10 deletions(-)

diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 63d56cda2b96..75f126538a72 100644
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -298,7 +298,7 @@ sbc_setup_write_same(struct se_cmd *cmd, unsigned char *flags, struct sbc_ops *o
return 0;
}

-static sense_reason_t xdreadwrite_callback(struct se_cmd *cmd)
+static sense_reason_t xdreadwrite_callback(struct se_cmd *cmd, bool success)
{
unsigned char *buf, *addr;
struct scatterlist *sg;
@@ -362,7 +362,7 @@ sbc_execute_rw(struct se_cmd *cmd)
cmd->data_direction);
}

-static sense_reason_t compare_and_write_post(struct se_cmd *cmd)
+static sense_reason_t compare_and_write_post(struct se_cmd *cmd, bool success)
{
struct se_device *dev = cmd->se_dev;

@@ -385,7 +385,7 @@ static sense_reason_t compare_and_write_post(struct se_cmd *cmd)
return TCM_NO_SENSE;
}

-static sense_reason_t compare_and_write_callback(struct se_cmd *cmd)
+static sense_reason_t compare_and_write_callback(struct se_cmd *cmd, bool success)
{
struct se_device *dev = cmd->se_dev;
struct scatterlist *write_sg = NULL, *sg;
@@ -400,11 +400,16 @@ static sense_reason_t compare_and_write_callback(struct se_cmd *cmd)

/*
* Handle early failure in transport_generic_request_failure(),
- * which will not have taken ->caw_mutex yet..
+ * which will not have taken ->caw_sem yet..
*/
- if (!cmd->t_data_sg || !cmd->t_bidi_data_sg)
+ if (!success && (!cmd->t_data_sg || !cmd->t_bidi_data_sg))
return TCM_NO_SENSE;
/*
+ * Handle special case for zero-length COMPARE_AND_WRITE
+ */
+ if (!cmd->data_length)
+ goto out;
+ /*
* Immediately exit + release dev->caw_sem if command has already
* been failed with a non-zero SCSI status.
*/
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 65ecaa1c59a7..b52bf3cad494 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1589,11 +1589,11 @@ void transport_generic_request_failure(struct se_cmd *cmd,
transport_complete_task_attr(cmd);
/*
* Handle special case for COMPARE_AND_WRITE failure, where the
- * callback is expected to drop the per device ->caw_mutex.
+ * callback is expected to drop the per device ->caw_sem.
*/
if ((cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE) &&
cmd->transport_complete_callback)
- cmd->transport_complete_callback(cmd);
+ cmd->transport_complete_callback(cmd, false);

switch (sense_reason) {
case TCM_NON_EXISTENT_LUN:
@@ -1942,8 +1942,12 @@ static void target_complete_ok_work(struct work_struct *work)
if (cmd->transport_complete_callback) {
sense_reason_t rc;

- rc = cmd->transport_complete_callback(cmd);
+ rc = cmd->transport_complete_callback(cmd, true);
if (!rc && !(cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE_POST)) {
+ if ((cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE) &&
+ !cmd->data_length)
+ goto queue_rsp;
+
return;
} else if (rc) {
ret = transport_send_check_condition_and_sense(cmd,
@@ -1957,6 +1961,7 @@ static void target_complete_ok_work(struct work_struct *work)
}
}

+queue_rsp:
switch (cmd->data_direction) {
case DMA_FROM_DEVICE:
spin_lock(&cmd->se_lun->lun_sep_lock);
@@ -2045,6 +2050,16 @@ static inline void transport_reset_sgl_orig(struct se_cmd *cmd)
static inline void transport_free_pages(struct se_cmd *cmd)
{
if (cmd->se_cmd_flags & SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC) {
+ /*
+ * Release special case READ buffer payload required for
+ * SG_TO_MEM_NOALLOC to function with COMPARE_AND_WRITE
+ */
+ if (cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE) {
+ transport_free_sgl(cmd->t_bidi_data_sg,
+ cmd->t_bidi_data_nents);
+ cmd->t_bidi_data_sg = NULL;
+ cmd->t_bidi_data_nents = 0;
+ }
transport_reset_sgl_orig(cmd);
return;
}
@@ -2193,6 +2208,7 @@ sense_reason_t
transport_generic_new_cmd(struct se_cmd *cmd)
{
int ret = 0;
+ bool zero_flag = !(cmd->se_cmd_flags & SCF_SCSI_DATA_CDB);

/*
* Determine is the TCM fabric module has already allocated physical
@@ -2201,7 +2217,6 @@ transport_generic_new_cmd(struct se_cmd *cmd)
*/
if (!(cmd->se_cmd_flags & SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC) &&
cmd->data_length) {
- bool zero_flag = !(cmd->se_cmd_flags & SCF_SCSI_DATA_CDB);

if ((cmd->se_cmd_flags & SCF_BIDI) ||
(cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE)) {
@@ -2224,6 +2239,20 @@ transport_generic_new_cmd(struct se_cmd *cmd)
cmd->data_length, zero_flag);
if (ret < 0)
return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+ } else if ((cmd->se_cmd_flags & SCF_COMPARE_AND_WRITE) &&
+ cmd->data_length) {
+ /*
+ * Special case for COMPARE_AND_WRITE with fabrics
+ * using SCF_PASSTHROUGH_SG_TO_MEM_NOALLOC.
+ */
+ u32 caw_length = cmd->t_task_nolb *
+ cmd->se_dev->dev_attrib.block_size;
+
+ ret = target_alloc_sgl(&cmd->t_bidi_data_sg,
+ &cmd->t_bidi_data_nents,
+ caw_length, zero_flag);
+ if (ret < 0)
+ return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
}
/*
* If this command is not a write we can execute it right here,
diff --git a/include/target/target_core_base.h b/include/target/target_core_base.h
index 38647a3441c9..085e6bedf393 100644
--- a/include/target/target_core_base.h
+++ b/include/target/target_core_base.h
@@ -457,7 +457,7 @@ struct se_cmd {
sense_reason_t (*execute_cmd)(struct se_cmd *);
sense_reason_t (*execute_rw)(struct se_cmd *, struct scatterlist *,
u32, enum dma_data_direction);
- sense_reason_t (*transport_complete_callback)(struct se_cmd *);
+ sense_reason_t (*transport_complete_callback)(struct se_cmd *, bool);

unsigned char *t_task_cdb;
unsigned char __t_task_cdb[TCM_MAX_COMMAND_SIZE];
--
2.3.7