[PATCH AUTOSEL 4.19 12/15] scsi: libiscsi: Fix NOP race condition

Sasha Levin
2020-11-25T15:40:48Z

From: Lee Duncan <lduncan@suse.com>

[ Upstream commit fe0a8a95e7134d0b44cd407bc0085b9ba8d8fe31 ]

iSCSI NOPs are sometimes "lost", mistakenly sent to the user-land iscsid
daemon instead of handled in the kernel, as they should be, resulting in a
message from the daemon like:

iscsid: Got nop in, but kernel supports nop handling.

This can occur because of the new forward- and back-locks, and the fact
that an iSCSI NOP response can occur before processing of the NOP send is
complete. This can result in "conn->ping_task" being NULL in
iscsi_nop_out_rsp(), when the pointer is actually in the process of being
set.

To work around this, we add a new state to the "ping_task" pointer. In
addition to NULL (not assigned) and a pointer (assigned), we add the state
"being set", which is signaled with an INVALID pointer (using "-1").

Link: https://lore.kernel.org/r/20201106193317.16993-1-leeman.duncan@gmail.com
Reviewed-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/scsi/libiscsi.c | 23 +++++++++++++++--------
include/scsi/libiscsi.h | 3 +++
2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
index 7a05c72717666..1c69515e870cb 100644
--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -571,8 +571,8 @@ static void iscsi_complete_task(struct iscsi_task *task, int state)
if (conn->task == task)
conn->task = NULL;

- if (conn->ping_task == task)
- conn->ping_task = NULL;
+ if (READ_ONCE(conn->ping_task) == task)
+ WRITE_ONCE(conn->ping_task, NULL);

/* release get from queueing */
__iscsi_put_task(task);
@@ -781,6 +781,9 @@ __iscsi_conn_send_pdu(struct iscsi_conn *conn, struct iscsi_hdr *hdr,
task->conn->session->age);
}

+ if (unlikely(READ_ONCE(conn->ping_task) == INVALID_SCSI_TASK))
+ WRITE_ONCE(conn->ping_task, task);
+
if (!ihost->workq) {
if (iscsi_prep_mgmt_task(conn, task))
goto free_task;
@@ -988,8 +991,11 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)
struct iscsi_nopout hdr;
struct iscsi_task *task;

- if (!rhdr && conn->ping_task)
- return -EINVAL;
+ if (!rhdr) {
+ if (READ_ONCE(conn->ping_task))
+ return -EINVAL;
+ WRITE_ONCE(conn->ping_task, INVALID_SCSI_TASK);
+ }

memset(&hdr, 0, sizeof(struct iscsi_nopout));
hdr.opcode = ISCSI_OP_NOOP_OUT | ISCSI_OP_IMMEDIATE;
@@ -1004,11 +1010,12 @@ static int iscsi_send_nopout(struct iscsi_conn *conn, struct iscsi_nopin *rhdr)

task = __iscsi_conn_send_pdu(conn, (struct iscsi_hdr *)&hdr, NULL, 0);
if (!task) {
+ if (!rhdr)
+ WRITE_ONCE(conn->ping_task, NULL);
iscsi_conn_printk(KERN_ERR, conn, "Could not send nopout\n");
return -EIO;
} else if (!rhdr) {
/* only track our nops */
- conn->ping_task = task;
conn->last_ping = jiffies;
}

@@ -1021,7 +1028,7 @@ static int iscsi_nop_out_rsp(struct iscsi_task *task,
struct iscsi_conn *conn = task->conn;
int rc = 0;

- if (conn->ping_task != task) {
+ if (READ_ONCE(conn->ping_task) != task) {
/*
* If this is not in response to one of our
* nops then it must be from userspace.
@@ -1961,7 +1968,7 @@ static void iscsi_start_tx(struct iscsi_conn *conn)
*/
static int iscsi_has_ping_timed_out(struct iscsi_conn *conn)
{
- if (conn->ping_task &&
+ if (READ_ONCE(conn->ping_task) &&
time_before_eq(conn->last_recv + (conn->recv_timeout * HZ) +
(conn->ping_timeout * HZ), jiffies))
return 1;
@@ -2096,7 +2103,7 @@ enum blk_eh_timer_return iscsi_eh_cmd_timed_out(struct scsi_cmnd *sc)
* Checking the transport already or nop from a cmd timeout still
* running
*/
- if (conn->ping_task) {
+ if (READ_ONCE(conn->ping_task)) {
task->have_checked_conn = true;
rc = BLK_EH_RESET_TIMER;
goto done;
diff --git a/include/scsi/libiscsi.h b/include/scsi/libiscsi.h
index c9bd935f4fd1c..1ee0f30ae190b 100644
--- a/include/scsi/libiscsi.h
+++ b/include/scsi/libiscsi.h
@@ -145,6 +145,9 @@ struct iscsi_task {
void *dd_data; /* driver/transport data */
};

+/* invalid scsi_task pointer */
+#define INVALID_SCSI_TASK (struct iscsi_task *)-1l
+
static inline int iscsi_task_has_unsol_data(struct iscsi_task *task)
{
return task->unsol_r2t.data_length > task->unsol_r2t.sent;
--
2.27.0