From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Christie Date: Tue, 27 Oct 2020 20:03:28 +0000 Subject: Re: [PATCH 2/2] target: iscsi: fix a race condition when aborting a task Message-Id: <71691FED-C164-482C-B629-A8B89B81E566@oracle.com> List-Id: References: <20201007145326.56850-1-mlombard@redhat.com> <20201007145326.56850-3-mlombard@redhat.com> <20daa17d-08e7-a412-4d33-bcf75587eca6@oracle.com> <1852a8bd-3edc-5c49-fa51-9afe52f125a8@redhat.com> <184667b1-032b-c36f-d1e7-5cfef961c763@oracle.com> In-Reply-To: <184667b1-032b-c36f-d1e7-5cfef961c763@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Maurizio Lombardi , "Martin K. Petersen" Cc: linux-scsi@vger.kernel.org, target-devel@vger.kernel.org, bvanassche@acm.org > On Oct 27, 2020, at 12:54 PM, Mike Christie 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 > 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. > + continue; > + } > se_cmd->transport_state |= CMD_T_FABRIC_STOP; > spin_unlock_irq(&se_cmd->t_state_lock); > } > -- > 1.8.3.1 >