target: Fix COMPARE_AND_WRITE with SG_TO_MEM_NOALLOC handling

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>
Cc: <stable@vger.kernel.org> # v3.12+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --git a/drivers/target/target_core_sbc.c b/drivers/target/target_core_sbc.c
index 315ff641408bb6122815392cd7de0c4fc7cdb8ef..0064ffe9a2193bec8b1cdfe03eb2c9e3c0ff4f6f 100644 (file)
--- a/drivers/target/target_core_sbc.c
+++ b/drivers/target/target_core_sbc.c
@@ -321,7 +321,7 @@ 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;
@@ -385,7 +385,7 @@ 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;
 
@@ -408,7 +408,7 @@ 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;
@@ -423,10 +423,15 @@ 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 --cc drivers/target/target_core_transport.c
Simple merge

diff --cc include/target/target_core_base.h
Simple merge