From: Michael Christie <firstname.lastname@example.org> To: Maurizio Lombardi <email@example.com> Cc: "Martin K. Petersen" <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org Subject: Re: [PATCH 2/2] target: iscsi: fix a race condition when aborting a task Date: Wed, 11 Nov 2020 15:37:51 +0000 Message-ID: <5D26782D-1249-4A2C-8BF9-7176D5B85F55@oracle.com> (raw) In-Reply-To: <email@example.com> > On Nov 11, 2020, at 8:58 AM, Maurizio Lombardi <firstname.lastname@example.org> wrote: > > > > Dne 11. 11. 20 v 3:16 Mike Christie napsal(a): >> Hey, I tested this out and I do not think this will happen. We will get stuck waiting on the TMF completion for the affected cmd/cmds. >> >> In conn_cmd_list we would have [CMD1 -> ABORT TMF]. Those cmds get moved to the tmp list. It might happen where CMD1's CMD_T_ABORTED bit is set, and iscsit_release_commands_from_conn will would put it back onto the conn_cmd_list. But then it will see the ABORT on the list. We will then wait on the ABORT in: >> >> iscsit_release_commands_from_conn -> iscsit_free_cmd -> transport_generic_free_cmd. > > Hi Mike, > > I'm not sure if I understood this part. > > The commands are moved to the tmp_list; > we check for CMD_T_ABORTED and eventually move the commands from tmp_list back to conn_cmd_list > because it's the abort task the one that should do the cleanup. I’m not sure what you mean here. Are you saying both CMD1’s se_cmd and the ABORT’s se_cmd will have the CMD_T_ABORTED bit set and will both go through the aborted_task callout? > > iscsit_release_commands_from_conn() then scans the tmp_list and calls iscsit_free_cmd()... but not against > those commands with CMD_T_ABORTED flag set because we just moved them back to conn_cmd_list > and aren't linked to tmp_list anymore. > > Am I missing something? If you have a SCSI READ/WRITE se_cmd (CMD1 in my example) and a ABORT se_cmd (ABORT TMF in my example) on the conn_cmd_list, then the ABORT’s se_cmd would not have the CMD_T_ABORTED bit set, right? If so, what sets it? If the SCSI R/W has the CMD_T_ABORTED bit set, we move it it back to the conn_cmd_list and the abort code path cleans it up. But then we still have the ABORT’s se_cmd on the tmp_list. We will then call transport_generic_free_cmd(wait_for_tasks=true) -> __transport_wait_for_tasks(fabric_stop=true) And wait for the ABORT to complete, and the ABORT does not complete until the last ref on the command it’s aborting completes. If you have a LUN RESET in the mix like: [CMD1 -> ABORT TMF -> LUN RESET TMF] Then CMD1 and the ABORT could have their CMD_T_ABORTED bit set. core_tmr_drain_tmr_list would call __target_check_io_state during the RESET processing. However, in this case, the LUN RESET’s se_cmd would not have the bit set, so we would end up waiting like I described for that to complete. In that case though the RESET waits for the cmds and tmfs it is cleaning up.
next prev parent reply index Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-07 14:53 [PATCH 0/2] fix race conditions with task aborts Maurizio Lombardi 2020-10-07 14:53 ` [PATCH 1/2] target: iscsi: prevent a race condition in iscsit_unmap_cmd() Maurizio Lombardi 2020-10-08 2:15 ` Bart Van Assche 2020-10-08 9:42 ` Maurizio Lombardi 2020-10-07 14:53 ` [PATCH 2/2] target: iscsi: fix a race condition when aborting a task Maurizio Lombardi 2020-10-22 2:42 ` Mike Christie 2020-10-27 13:49 ` Maurizio Lombardi 2020-10-27 17:54 ` Mike Christie 2020-10-27 20:03 ` Michael Christie 2020-10-28 17:09 ` Maurizio Lombardi 2020-10-28 20:37 ` Mike Christie 2020-11-10 21:29 ` Maurizio Lombardi 2020-11-10 23:08 ` Mike Christie 2020-11-11 2:16 ` Mike Christie 2020-11-11 14:58 ` Maurizio Lombardi 2020-11-11 15:37 ` Michael Christie [this message] 2020-11-11 15:48 ` Maurizio Lombardi
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