[PATCH] scsi: target: Clear cmd_cnt when initial counter enrollment fails

[PATCH] scsi: target: Clear cmd_cnt when initial counter enrollment fails

[Leon Romanovsky]

From: Leon Romanovsky <leonro@nvidia.com>

When target_get_sess_cmd() fails during session shutdown because
percpu_ref_tryget_live() returns false, the command keeps the
se_cmd->cmd_cnt pointer that __target_init_cmd() assigned earlier without
owning a reference. Final release through target_release_cmd_kref() then
issues an unmatched percpu_ref_put().

Commit 8e288be8606a ("scsi: target: Pass in cmd counter to use during cmd
setup") moved the cmd_cnt assignment ahead of the reference acquisition.
Clear se_cmd->cmd_cnt whenever the initial target_get_sess_cmd() fails in
target_init_cmd() and target_submit_tmr(), so release performs exactly one
matching put per acquired reference.

Fixes: 8e288be8606a ("scsi: target: Pass in cmd counter to use during cmd setup")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
---
Found by sashiko.
---
 drivers/target/target_core_transport.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index fad03a15c969..dcfe94594916 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -1734,6 +1734,7 @@ int target_init_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
 		    u32 data_length, int task_attr, int data_dir, int flags)
 {
 	struct se_portal_group *se_tpg;
+	int ret;
 
 	se_tpg = se_sess->se_tpg;
 	BUG_ON(!se_tpg);
@@ -1763,7 +1764,11 @@ int target_init_cmd(struct se_cmd *se_cmd, struct se_session *se_sess,
 	 * necessary for fabrics using TARGET_SCF_ACK_KREF that expect a second
 	 * kref_put() to happen during fabric packet acknowledgement.
 	 */
-	return target_get_sess_cmd(se_cmd, flags & TARGET_SCF_ACK_KREF);
+	ret = target_get_sess_cmd(se_cmd, flags & TARGET_SCF_ACK_KREF);
+	if (ret)
+		se_cmd->cmd_cnt = NULL;
+
+	return ret;
 }
 EXPORT_SYMBOL_GPL(target_init_cmd);
 
@@ -2039,8 +2044,10 @@ int target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
 	 * allocation failure.
 	 */
 	ret = core_tmr_alloc_req(se_cmd, fabric_tmr_ptr, tm_type, gfp);
-	if (ret < 0)
+	if (ret < 0) {
+		se_cmd->cmd_cnt = NULL;
 		return -ENOMEM;
+	}
 
 	if (tm_type == TMR_ABORT_TASK)
 		se_cmd->se_tmr_req->ref_task_tag = tag;
@@ -2048,6 +2055,7 @@ int target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
 	/* See target_submit_cmd for commentary */
 	ret = target_get_sess_cmd(se_cmd, flags & TARGET_SCF_ACK_KREF);
 	if (ret) {
+		se_cmd->cmd_cnt = NULL;
 		core_tmr_release_req(se_cmd->se_tmr_req);
 		return ret;
 	}

---
base-commit: 74f49255492a62658f36bf2578d7916f1c6ffad1
change-id: 20260721-reference-count-underflow-in-target-a7e580e549ca

Best regards,
--  
Leon Romanovsky <leonro@nvidia.com>

Re: [PATCH] scsi: target: Clear cmd_cnt when initial counter enrollment fails

[Mike Christie]

On 7/22/26 1:30 AM, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@nvidia.com>
> 
> When target_get_sess_cmd() fails during session shutdown because
> percpu_ref_tryget_live() returns false, the command keeps the
> se_cmd->cmd_cnt pointer that __target_init_cmd() assigned earlier without
> owning a reference. Final release through target_release_cmd_kref() then
> issues an unmatched percpu_ref_put().
> 
> Commit 8e288be8606a ("scsi: target: Pass in cmd counter to use during cmd
> setup") moved the cmd_cnt assignment ahead of the reference acquisition.
> Clear se_cmd->cmd_cnt whenever the initial target_get_sess_cmd() fails in
> target_init_cmd() and target_submit_tmr(), so release performs exactly one
> matching put per acquired reference.
> 
> Fixes: 8e288be8606a ("scsi: target: Pass in cmd counter to use during cmd setup")
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

Reviewed-by: Mike Christie <michael.christie@oracle.com>

Re: [PATCH] scsi: target: Clear cmd_cnt when initial counter enrollment fails

[Martin K. Petersen]

On Wed, 22 Jul 2026 09:30:10 +0300, Leon Romanovsky wrote:

> When target_get_sess_cmd() fails during session shutdown because
> percpu_ref_tryget_live() returns false, the command keeps the
> se_cmd->cmd_cnt pointer that __target_init_cmd() assigned earlier without
> owning a reference. Final release through target_release_cmd_kref() then
> issues an unmatched percpu_ref_put().
> 
> Commit 8e288be8606a ("scsi: target: Pass in cmd counter to use during cmd
> setup") moved the cmd_cnt assignment ahead of the reference acquisition.
> Clear se_cmd->cmd_cnt whenever the initial target_get_sess_cmd() fails in
> target_init_cmd() and target_submit_tmr(), so release performs exactly one
> matching put per acquired reference.
> 
> [...]

Applied to 7.2/scsi-fixes, thanks!

[1/1] scsi: target: Clear cmd_cnt when initial counter enrollment fails
      https://git.kernel.org/mkp/scsi/c/a8ddfd2425bb

-- 
Martin K. Petersen