On 10/28/20 12:09 PM, Maurizio Lombardi wrote:
Dne 27. 10. 20 v 21:03 Michael Christie napsal(a):
On Oct 27, 2020, at 12:54 PM, Mike Christie <michael.christie@xxxxxxxxxx> wrote:
On 10/27/20 8:49 AM, Maurizio Lombardi wrote:
Hello Mike,
Dne 22. 10. 20 v 4:42 Mike Christie napsal(a):
If we free the cmd from the abort path, then for your conn stop plus abort race case, could we do:
1. thread1 runs iscsit_release_commands_from_conn and sets CMD_T_FABRIC_STOP.
2. thread2 runs iscsit_aborted_task and then does __iscsit_free_cmd. It then returns from the aborted_task callout and we finish target_handle_abort and do:
target_handle_abort -> transport_cmd_check_stop_to_fabric -> lio_check_stop_free -> target_put_sess_cmd
The cmd is now freed.
3. thread1 now finishes iscsit_release_commands_from_conn and runs iscsit_free_cmd while accessing a command we just released.
Thanks for the review!
There are definitely some problems with task aborts and commands' refcounting *
but this is a different bug than the one this patch is trying to solve (a race to list_del_init());
unless you are saying that abort tasks should never be executed when the connection
is going down and we have to prevent such cases from happening at all.
Yeah, I think if we prevent the race then we fix the refcount issue and your issue.
Here is a patch that is only compile tested:
From 209709bcedd9a6ce6003e6bb86f3ebf547dca6af Mon Sep 17 00:00:00 2001
From: Mike Christie <michael.christie@xxxxxxxxxx>
Date: Tue, 27 Oct 2020 12:30:53 -0500
Subject: [PATCH] iscsi target: fix cmd abort vs fabric stop race
The abort and cmd stop paths can race where:
1. thread1 runs iscsit_release_commands_from_conn and sets
CMD_T_FABRIC_STOP.
2. thread2 runs iscsit_aborted_task and then does __iscsit_free_cmd. It
then returns from the aborted_task callout and we finish
target_handle_abort and do:
target_handle_abort -> transport_cmd_check_stop_to_fabric ->
lio_check_stop_free -> target_put_sess_cmd
The cmd is now freed.
3. thread1 now finishes iscsit_release_commands_from_conn and runs
iscsit_free_cmd while accessing a command we just released.
In __target_check_io_state we check for CMD_T_FABRIC_STOP and set the
CMD_T_ABORTED if the driver is not cleaning up the cmd because of
a session shutdown. However, iscsit_release_commands_from_conn only
sets the CMD_T_FABRIC_STOP and does not check to see if the abort path
has claimed completion ownership of the command.
This adds a check in iscsit_release_commands_from_conn so only the
abort or fabric stop path cleanup the command.
---
drivers/target/iscsi/iscsi_target.c | 13 +++++++++++--
1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index f77e5ee..85027d3 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -483,8 +483,7 @@ int iscsit_queue_rsp(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
void iscsit_aborted_task(struct iscsi_conn *conn, struct iscsi_cmd *cmd)
{
spin_lock_bh(&conn->cmd_lock);
- if (!list_empty(&cmd->i_conn_node) &&
- !(cmd->se_cmd.transport_state & CMD_T_FABRIC_STOP))
+ if (!list_empty(&cmd->i_conn_node))
list_del_init(&cmd->i_conn_node);
spin_unlock_bh(&conn->cmd_lock);
@@ -4088,6 +4087,16 @@ static void iscsit_release_commands_from_conn(struct iscsi_conn *conn)
if (se_cmd->se_tfo != NULL) {
spin_lock_irq(&se_cmd->t_state_lock);
+ if (se_cmd->transport_state & CMD_T_ABORTED) {
+ /*
+ * LIO's abort path owns the cleanup for this,
+ * so put it back on the list and let
+ * aborted_task handle it.
+ */
+ list_add_tail(&cmd->i_conn_node,
+ &conn->conn_cmd_list);
That should have been a move from the tmp list back to the conn_cmd_list.
Nice, it looks simple and I will test it.
I am a bit worried there could be other possible race conditions.
Example:
thread1: connection is going to be closed,
iscsit_release_commands_from_conn() finds a command that is about
to be aborted, re-adds it to conn_cmd_list and proceeds.
iscsit_close_connection() decreases the conn usage count and finally calls iscsit_free_conn(conn)
that destroys the conn structure.
thread2: iscsit_aborted_task() gets called and tries to lock the conn->cmd_lock spinlock, dereferencing
an invalid pointer.
Nice catch. You are right.
Possible solutions that I can think of:
- Make iscsit_release_commands_from_conn() wait for the abort task to finish
Yeah you could set a completion in there then have aborted_task do the
complete() call maybe?
There is also the transport_cmd_check_stop_to_fabric
t_transport_stop_comp completion and transport_wait_for_tasks pairing
that seems close to what we want. I think we would have to change it to
make it work for this case. Oh yeah, that is more of a brain stroming
guess than a review type of comment :)
or
- abort handler could hold a reference to the conn structure so that iscsit_close_connection()
will sleep when calling iscsit_check_conn_usage_count(conn) until abort finishes.
