* [PATCH v2] target: core: remove from tmr_list at lun unlink
@ 2021-04-16 9:21 Dmitry Bogdanov
2021-04-16 21:38 ` Mike Christie
` (2 more replies)
0 siblings, 3 replies; 7+ messages in thread
From: Dmitry Bogdanov @ 2021-04-16 9:21 UTC (permalink / raw)
To: Martin Petersen, target-devel
Cc: linux-scsi, linux, Dmitry Bogdanov, Roman Bolshakov
Currently TMF commands are removed from de_device.dev_tmf_list at
the very end of se_cmd lifecycle. But se_lun unlinks from se_cmd
up on a command status (response) is queued in transport layer.
It means that LUN and backend device can be deleted meantime and at
the moment of repsonse completion a panic is occured:
target_tmr_work()
cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
- // - // - // -
<<<--- lun remove
<<<--- core backend device remove
- // - // - // -
qlt_handle_abts_completion()
tfo->free_mcmd()
transport_generic_free_cmd()
target_put_sess_cmd()
core_tmr_release_req() {
if (dev) { // backend device, can not be null
spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH
Call Trace:
NIP [c000000000e1683c] _raw_spin_lock_irqsave+0x2c/0xc0
LR [c00800000e433338] core_tmr_release_req+0x40/0xa0 [target_core_mod]
Call Trace:
(unreliable)
0x0
target_put_sess_cmd+0x2a0/0x370 [target_core_mod]
transport_generic_free_cmd+0x6c/0x1b0 [target_core_mod]
tcm_qla2xxx_complete_mcmd+0x28/0x50 [tcm_qla2xxx]
process_one_work+0x2c4/0x5c0
worker_thread+0x88/0x690
For FC protocol it is a race condition, but for iSCSI protocol it is
easyly reproduced by manual sending iSCSI commands:
- Send some SCSI sommand
- Send Abort of that command over iSCSI
- Remove LUN on target
- Send next iSCSI command to acknowledge the Abort_Response
- target panics
There is no sense to keep the command in tmr_list until response
completion, so move the removal from tmr_list from the response
completion to the response queueing when lun is unlinked.
Move the removal from state list too as it is a subject to the same
race condition.
Fixes: c66ac9db8d4a ("[SCSI] target: Add LIO target core v4.0.0-rc6")
Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
---
v2:
fix cmd stuck in tmr list in error case in iscsi
move clearing cmd->se_lun to transport_lun_remove_cmd
The issue exists from the very begining.
I uploaded a scapy script that helps to reproduce the issue at
https://gist.github.com/logost/cb93df41dd2432454324449b390403c4
---
drivers/target/iscsi/iscsi_target.c | 2 +-
drivers/target/target_core_tmr.c | 9 --------
drivers/target/target_core_transport.c | 29 +++++++++++++++++++-------
3 files changed, 23 insertions(+), 17 deletions(-)
diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
index d0e7ed8f28cc..3311b031a812 100644
--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -2142,7 +2142,7 @@ iscsit_handle_task_mgt_cmd(struct iscsi_conn *conn, struct iscsi_cmd *cmd,
* TMR TASK_REASSIGN.
*/
iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
- target_put_sess_cmd(&cmd->se_cmd);
+ transport_generic_free_cmd(&cmd->se_cmd, false);
return 0;
}
EXPORT_SYMBOL(iscsit_handle_task_mgt_cmd);
diff --git a/drivers/target/target_core_tmr.c b/drivers/target/target_core_tmr.c
index 7347285471fa..323a173010c1 100644
--- a/drivers/target/target_core_tmr.c
+++ b/drivers/target/target_core_tmr.c
@@ -50,15 +50,6 @@ EXPORT_SYMBOL(core_tmr_alloc_req);
void core_tmr_release_req(struct se_tmr_req *tmr)
{
- struct se_device *dev = tmr->tmr_dev;
- unsigned long flags;
-
- if (dev) {
- spin_lock_irqsave(&dev->se_tmr_lock, flags);
- list_del_init(&tmr->tmr_list);
- spin_unlock_irqrestore(&dev->se_tmr_lock, flags);
- }
-
kfree(tmr);
}
diff --git a/drivers/target/target_core_transport.c b/drivers/target/target_core_transport.c
index 5ecb9f18a53d..34b20c0646ab 100644
--- a/drivers/target/target_core_transport.c
+++ b/drivers/target/target_core_transport.c
@@ -667,6 +667,20 @@ static void target_remove_from_state_list(struct se_cmd *cmd)
spin_unlock_irqrestore(&dev->queues[cmd->cpuid].lock, flags);
}
+static void target_remove_from_tmr_list(struct se_cmd *cmd)
+{
+ struct se_device *dev = NULL;
+ unsigned long flags;
+
+ if (cmd->se_cmd_flags & SCF_SCSI_TMR_CDB)
+ dev = cmd->se_tmr_req->tmr_dev;
+
+ if (dev) {
+ spin_lock_irqsave(&dev->se_tmr_lock, flags);
+ list_del_init(&cmd->se_tmr_req->tmr_list);
+ spin_unlock_irqrestore(&dev->se_tmr_lock, flags);
+ }
+}
/*
* This function is called by the target core after the target core has
* finished processing a SCSI command or SCSI TMF. Both the regular command
@@ -678,13 +692,6 @@ static int transport_cmd_check_stop_to_fabric(struct se_cmd *cmd)
{
unsigned long flags;
- target_remove_from_state_list(cmd);
-
- /*
- * Clear struct se_cmd->se_lun before the handoff to FE.
- */
- cmd->se_lun = NULL;
-
spin_lock_irqsave(&cmd->t_state_lock, flags);
/*
* Determine if frontend context caller is requesting the stopping of
@@ -719,8 +726,16 @@ static void transport_lun_remove_cmd(struct se_cmd *cmd)
if (!lun)
return;
+ target_remove_from_state_list(cmd);
+ target_remove_from_tmr_list(cmd);
+
if (cmpxchg(&cmd->lun_ref_active, true, false))
percpu_ref_put(&lun->lun_ref);
+
+ /*
+ * Clear struct se_cmd->se_lun before the handoff to FE.
+ */
+ cmd->se_lun = NULL;
}
static void target_complete_failure_work(struct work_struct *work)
--
2.25.1
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH v2] target: core: remove from tmr_list at lun unlink
2021-04-16 9:21 [PATCH v2] target: core: remove from tmr_list at lun unlink Dmitry Bogdanov
@ 2021-04-16 21:38 ` Mike Christie
2021-04-16 21:41 ` Mike Christie
2021-04-16 22:39 ` Mike Christie
2021-04-17 9:39 ` Konstantin Shelekhin
2 siblings, 1 reply; 7+ messages in thread
From: Mike Christie @ 2021-04-16 21:38 UTC (permalink / raw)
To: Dmitry Bogdanov, Martin Petersen, target-devel
Cc: linux-scsi, linux, Roman Bolshakov
On 4/16/21 4:21 AM, Dmitry Bogdanov wrote:
> Currently TMF commands are removed from de_device.dev_tmf_list at
> the very end of se_cmd lifecycle. But se_lun unlinks from se_cmd
> up on a command status (response) is queued in transport layer.
> It means that LUN and backend device can be deleted meantime and at
> the moment of repsonse completion a panic is occured:
>
> target_tmr_work()
> cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
> transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
> - // - // - // -
> <<<--- lun remove
> <<<--- core backend device remove
> - // - // - // -
> qlt_handle_abts_completion()
> tfo->free_mcmd()
> transport_generic_free_cmd()
> target_put_sess_cmd()
> core_tmr_release_req() {
> if (dev) { // backend device, can not be null
> spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH
>
Sorry about this. I was thinking about this patch some more while
reviewing this version.
Is there another race possible?
1. We have a cmd running in lio.
2. The initiator times it out and sends tmf.
3. cmd completes.
4. target_submit_tmr has called transport_lookup_tmr_lun.
5. transport_lookup_tmr_lun has set se_dev and tmr_dev.
6. You now remove the lun and device.
7. Now you crash on the dev references.
I think we need to do a percpu_ref_tryget_live in transport_lookup_tmr_lun
like is done in transport_lookup_cmd_lun. If successful set
se_cmd->lun_ref_active = true;
If we get the ref, we drop it in transport_lun_remove_cmd like with
the non tmr case.
Combined with this patch then I think we are ok for all races.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] target: core: remove from tmr_list at lun unlink
2021-04-16 21:38 ` Mike Christie
@ 2021-04-16 21:41 ` Mike Christie
0 siblings, 0 replies; 7+ messages in thread
From: Mike Christie @ 2021-04-16 21:41 UTC (permalink / raw)
To: Dmitry Bogdanov, Martin Petersen, target-devel
Cc: linux-scsi, linux, Roman Bolshakov
On 4/16/21 4:38 PM, Mike Christie wrote:
> On 4/16/21 4:21 AM, Dmitry Bogdanov wrote:
>> Currently TMF commands are removed from de_device.dev_tmf_list at
>> the very end of se_cmd lifecycle. But se_lun unlinks from se_cmd
>> up on a command status (response) is queued in transport layer.
>> It means that LUN and backend device can be deleted meantime and at
>> the moment of repsonse completion a panic is occured:
>>
>> target_tmr_work()
>> cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
>> transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
>> - // - // - // -
>> <<<--- lun remove
>> <<<--- core backend device remove
>> - // - // - // -
>> qlt_handle_abts_completion()
>> tfo->free_mcmd()
>> transport_generic_free_cmd()
>> target_put_sess_cmd()
>> core_tmr_release_req() {
>> if (dev) { // backend device, can not be null
>> spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH
>>
>
> Sorry about this. I was thinking about this patch some more while
> reviewing this version.
>
> Is there another race possible?
>
> 1. We have a cmd running in lio.
> 2. The initiator times it out and sends tmf.
> 3. cmd completes.
> 4. target_submit_tmr has called transport_lookup_tmr_lun.
> 5. transport_lookup_tmr_lun has set se_dev and tmr_dev.
> 6. You now remove the lun and device.
> 7. Now you crash on the dev references.
>
> I think we need to do a percpu_ref_tryget_live in transport_lookup_tmr_lun
> like is done in transport_lookup_cmd_lun. If successful set
>
> se_cmd->lun_ref_active = true;
>
> If we get the ref, we drop it in transport_lun_remove_cmd like with
> the non tmr case.
>
Ignore this. I see we do a percpu_ref_tryget_live in there already.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] target: core: remove from tmr_list at lun unlink
2021-04-16 9:21 [PATCH v2] target: core: remove from tmr_list at lun unlink Dmitry Bogdanov
2021-04-16 21:38 ` Mike Christie
@ 2021-04-16 22:39 ` Mike Christie
2021-04-16 22:50 ` Mike Christie
2021-04-17 9:39 ` Konstantin Shelekhin
2 siblings, 1 reply; 7+ messages in thread
From: Mike Christie @ 2021-04-16 22:39 UTC (permalink / raw)
To: Dmitry Bogdanov, Martin Petersen, target-devel
Cc: linux-scsi, linux, Roman Bolshakov
On 4/16/21 4:21 AM, Dmitry Bogdanov wrote:
> Currently TMF commands are removed from de_device.dev_tmf_list at
> the very end of se_cmd lifecycle. But se_lun unlinks from se_cmd
> up on a command status (response) is queued in transport layer.
> It means that LUN and backend device can be deleted meantime and at
> the moment of repsonse completion a panic is occured:
>
> target_tmr_work()
> cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
> transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
> - // - // - // -
> <<<--- lun remove
> <<<--- core backend device remove
> - // - // - // -
> qlt_handle_abts_completion()
> tfo->free_mcmd()
> transport_generic_free_cmd()
> target_put_sess_cmd()
> core_tmr_release_req() {
> if (dev) { // backend device, can not be null
> spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH
>
> Call Trace:
> NIP [c000000000e1683c] _raw_spin_lock_irqsave+0x2c/0xc0
> LR [c00800000e433338] core_tmr_release_req+0x40/0xa0 [target_core_mod]
> Call Trace:
> (unreliable)
> 0x0
> target_put_sess_cmd+0x2a0/0x370 [target_core_mod]
> transport_generic_free_cmd+0x6c/0x1b0 [target_core_mod]
> tcm_qla2xxx_complete_mcmd+0x28/0x50 [tcm_qla2xxx]
> process_one_work+0x2c4/0x5c0
> worker_thread+0x88/0x690
>
> For FC protocol it is a race condition, but for iSCSI protocol it is
> easyly reproduced by manual sending iSCSI commands:
> - Send some SCSI sommand
> - Send Abort of that command over iSCSI
> - Remove LUN on target
> - Send next iSCSI command to acknowledge the Abort_Response
> - target panics
>
> There is no sense to keep the command in tmr_list until response
> completion, so move the removal from tmr_list from the response
> completion to the response queueing when lun is unlinked.
> Move the removal from state list too as it is a subject to the same
> race condition.
>
> Fixes: c66ac9db8d4a ("[SCSI] target: Add LIO target core v4.0.0-rc6")
> Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
> Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
>
> ---
> v2:
> fix cmd stuck in tmr list in error case in iscsi
> move clearing cmd->se_lun to transport_lun_remove_cmd
>
> The issue exists from the very begining.
> I uploaded a scapy script that helps to reproduce the issue at
> https://urldefense.com/v3/__https://gist.github.com/logost/cb93df41dd2432454324449b390403c4__;!!GqivPVa7Brio!MjANCRIp5ZrtKYonxEKclROOwOe7s-adKHLiUd2Njis6m1774RMpLGNkHyapFf68BwFr$
> ---
> drivers/target/iscsi/iscsi_target.c | 2 +-
> drivers/target/target_core_tmr.c | 9 --------
> drivers/target/target_core_transport.c | 29 +++++++++++++++++++-------
> 3 files changed, 23 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
> index d0e7ed8f28cc..3311b031a812 100644
> --- a/drivers/target/iscsi/iscsi_target.c
> +++ b/drivers/target/iscsi/iscsi_target.c
> @@ -2142,7 +2142,7 @@ iscsit_handle_task_mgt_cmd(struct iscsi_conn *conn, struct iscsi_cmd *cmd,
> * TMR TASK_REASSIGN.
> */
> iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
> - target_put_sess_cmd(&cmd->se_cmd);
> + transport_generic_free_cmd(&cmd->se_cmd, false);
> return 0;
> }
Doh. I see how I got all confused. I guess this path leaks the lun_ref
taken by transport_lookup_tmr_lun. It looks like an old issue and nothing
to do with your patch.
I'm not sure if we are supposed to be calling transport_generic_free_cmd
twice. It looks like it works ok, because your patch added the "cmd->se_lun = NULL"
in transport_lun_remove_cmd, so we won't do a double list deletion.
It feels dirty though. I can feel Bart saying, "Mike did you see the comment
at the top of the function". :)
Maybe it's best to more cleanly unwind what was setup in the rror path. I think we
can fix lun_ref leak too.
So instead of doing transport_generic_free_cmd above do transport_lun_remove_cmd
to match/undo the transport_lookup_tmr_lun call in iscsit_handle_task_mgt_cmd?
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] target: core: remove from tmr_list at lun unlink
2021-04-16 22:39 ` Mike Christie
@ 2021-04-16 22:50 ` Mike Christie
2021-04-21 15:07 ` Dmitriy Bogdanov
0 siblings, 1 reply; 7+ messages in thread
From: Mike Christie @ 2021-04-16 22:50 UTC (permalink / raw)
To: Dmitry Bogdanov, Martin Petersen, target-devel
Cc: linux-scsi, linux, Roman Bolshakov
On 4/16/21 5:39 PM, Mike Christie wrote:
> On 4/16/21 4:21 AM, Dmitry Bogdanov wrote:
>> Currently TMF commands are removed from de_device.dev_tmf_list at
>> the very end of se_cmd lifecycle. But se_lun unlinks from se_cmd
>> up on a command status (response) is queued in transport layer.
>> It means that LUN and backend device can be deleted meantime and at
>> the moment of repsonse completion a panic is occured:
>>
>> target_tmr_work()
>> cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
>> transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
>> - // - // - // -
>> <<<--- lun remove
>> <<<--- core backend device remove
>> - // - // - // -
>> qlt_handle_abts_completion()
>> tfo->free_mcmd()
>> transport_generic_free_cmd()
>> target_put_sess_cmd()
>> core_tmr_release_req() {
>> if (dev) { // backend device, can not be null
>> spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH
>>
>> Call Trace:
>> NIP [c000000000e1683c] _raw_spin_lock_irqsave+0x2c/0xc0
>> LR [c00800000e433338] core_tmr_release_req+0x40/0xa0 [target_core_mod]
>> Call Trace:
>> (unreliable)
>> 0x0
>> target_put_sess_cmd+0x2a0/0x370 [target_core_mod]
>> transport_generic_free_cmd+0x6c/0x1b0 [target_core_mod]
>> tcm_qla2xxx_complete_mcmd+0x28/0x50 [tcm_qla2xxx]
>> process_one_work+0x2c4/0x5c0
>> worker_thread+0x88/0x690
>>
>> For FC protocol it is a race condition, but for iSCSI protocol it is
>> easyly reproduced by manual sending iSCSI commands:
>> - Send some SCSI sommand
>> - Send Abort of that command over iSCSI
>> - Remove LUN on target
>> - Send next iSCSI command to acknowledge the Abort_Response
>> - target panics
>>
>> There is no sense to keep the command in tmr_list until response
>> completion, so move the removal from tmr_list from the response
>> completion to the response queueing when lun is unlinked.
>> Move the removal from state list too as it is a subject to the same
>> race condition.
>>
>> Fixes: c66ac9db8d4a ("[SCSI] target: Add LIO target core v4.0.0-rc6")
>> Reviewed-by: Roman Bolshakov <r.bolshakov@yadro.com>
>> Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
>>
>> ---
>> v2:
>> fix cmd stuck in tmr list in error case in iscsi
>> move clearing cmd->se_lun to transport_lun_remove_cmd
>>
>> The issue exists from the very begining.
>> I uploaded a scapy script that helps to reproduce the issue at
>> https://urldefense.com/v3/__https://gist.github.com/logost/cb93df41dd2432454324449b390403c4__;!!GqivPVa7Brio!MjANCRIp5ZrtKYonxEKclROOwOe7s-adKHLiUd2Njis6m1774RMpLGNkHyapFf68BwFr$
>> ---
>> drivers/target/iscsi/iscsi_target.c | 2 +-
>> drivers/target/target_core_tmr.c | 9 --------
>> drivers/target/target_core_transport.c | 29 +++++++++++++++++++-------
>> 3 files changed, 23 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/target/iscsi/iscsi_target.c b/drivers/target/iscsi/iscsi_target.c
>> index d0e7ed8f28cc..3311b031a812 100644
>> --- a/drivers/target/iscsi/iscsi_target.c
>> +++ b/drivers/target/iscsi/iscsi_target.c
>> @@ -2142,7 +2142,7 @@ iscsit_handle_task_mgt_cmd(struct iscsi_conn *conn, struct iscsi_cmd *cmd,
>> * TMR TASK_REASSIGN.
>> */
>> iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
>> - target_put_sess_cmd(&cmd->se_cmd);
>> + transport_generic_free_cmd(&cmd->se_cmd, false);
>> return 0;
>> }
>
> Doh. I see how I got all confused. I guess this path leaks the lun_ref
> taken by transport_lookup_tmr_lun. It looks like an old issue and nothing
> to do with your patch.
>
> I'm not sure if we are supposed to be calling transport_generic_free_cmd
> twice. It looks like it works ok, because your patch added the "cmd->se_lun = NULL"
> in transport_lun_remove_cmd, so we won't do a double list deletion.
> It feels dirty though. I can feel Bart saying, "Mike did you see the comment
> at the top of the function". :)
>
> Maybe it's best to more cleanly unwind what was setup in the rror path. I think we
> can fix lun_ref leak too.
>
> So instead of doing transport_generic_free_cmd above do transport_lun_remove_cmd
> to match/undo the transport_lookup_tmr_lun call in iscsit_handle_task_mgt_cmd?
Shoot. I'm all over the place. I think the root issue is my original comment on the v1
patch was wrong.
On a failure we would still do:
iscsit_free_cmd -> transport_generic_free_cmd -> transport_lun_remove_cmd
right? So we don't need any change in the iscsi target. It should all
just work.
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH v2] target: core: remove from tmr_list at lun unlink
2021-04-16 9:21 [PATCH v2] target: core: remove from tmr_list at lun unlink Dmitry Bogdanov
2021-04-16 21:38 ` Mike Christie
2021-04-16 22:39 ` Mike Christie
@ 2021-04-17 9:39 ` Konstantin Shelekhin
2 siblings, 0 replies; 7+ messages in thread
From: Konstantin Shelekhin @ 2021-04-17 9:39 UTC (permalink / raw)
To: Dmitry Bogdanov
Cc: Martin Petersen, target-devel, linux-scsi, linux, Roman Bolshakov
On Fri, Apr 16, 2021 at 12:21:46PM +0300, Dmitry Bogdanov wrote:
> @@ -719,8 +726,16 @@ static void transport_lun_remove_cmd(struct se_cmd *cmd)
> if (!lun)
> return;
>
> + target_remove_from_state_list(cmd);
> + target_remove_from_tmr_list(cmd);
> +
> if (cmpxchg(&cmd->lun_ref_active, true, false))
> percpu_ref_put(&lun->lun_ref);
> +
> + /*
> + * Clear struct se_cmd->se_lun before the handoff to FE.
> + */
> + cmd->se_lun = NULL;
> }
Sadly we just found out that this code is racing with
core_tmr_drain_tmr_list(). If LUN RESET comes in while there are still
some outstanding ABORT TASK functions left, the following sequence is
possible:
1. During LUN RESET processing core_tmr_drain_tmr_list() is called
2. During ABORT TASK processing transport_lun_remove_cmd() is called
at the sime time
3. core_tmr_drain_tmr_list() acquires &dev->se_tmr_lock lock and moves
TMRs to the on-stack drain_tmr_list
4. core_tmr_drain_tmr_list() releases &dev->se_tmr_lock and starts
working on the drain_tmr_list
5. At the same moment target_remove_from_tmr_list() is called
6. It acquires &dev->se_tmr_lock, removes TMR from the list by
list_del_init() and releases &dev->se_tmr_lock
What happens next is this:
[ 391.438244] LUN_RESET: releasing TMR 00000000e2ee2634 Function: 0x01, Response: 0x05, t_state: 11
[ 391.438246] LUN_RESET: releasing TMR 00000000e2ee2634 Function: 0x01, Response: 0x05, t_state: 11
The same TMR is being pulled out twice out of the drain_tmr_list. This
happens because there are no locks that prevent the list traversal in
core_tmr_drain_tmr_list() and the list element removal in
target_remove_from_tmr_list() from being executed concurrently. So
list_del_init() in target_remove_from_tmr_list() calls INIT_LIST_HEAD()
and tmr_p->next now points to tmr_p.
Hence the following warnings:
[ 391.438300] WARNING: CPU: 12 PID: 20064 at ../drivers/target/target_core_transport.c:2785
...
[ 391.438448] WARNING: CPU: 12 PID: 20064 at ../lib/refcount.c:28 refcount_warn_saturate+0x224/0x240
This issue also prevents other TMRs from being released, resulting in a
stuck session. Not always, since sometimes drain_tmr_list only contains
one element, but still possible.
^ permalink raw reply [flat|nested] 7+ messages in thread
* RE: [PATCH v2] target: core: remove from tmr_list at lun unlink
2021-04-16 22:50 ` Mike Christie
@ 2021-04-21 15:07 ` Dmitriy Bogdanov
0 siblings, 0 replies; 7+ messages in thread
From: Dmitriy Bogdanov @ 2021-04-21 15:07 UTC (permalink / raw)
To: Mike Christie, Martin Petersen, target-devel
Cc: linux-scsi, linux, Roman Bolshakov
Hi Mike,
>>> --- a/drivers/target/iscsi/iscsi_target.c
>>> +++ b/drivers/target/iscsi/iscsi_target.c
>>> @@ -2142,7 +2142,7 @@ iscsit_handle_task_mgt_cmd(struct iscsi_conn *conn, struct iscsi_cmd *cmd,
>>> * TMR TASK_REASSIGN.
>>> */
>>> iscsit_add_cmd_to_response_queue(cmd, conn, cmd->i_state);
>>> - target_put_sess_cmd(&cmd->se_cmd);
>>> + transport_generic_free_cmd(&cmd->se_cmd, false);
>>> return 0;
>>> }
>>
>> Doh. I see how I got all confused. I guess this path leaks the lun_ref
>> taken by transport_lookup_tmr_lun. It looks like an old issue and
>> nothing to do with your patch.
>> I'm not sure if we are supposed to be calling
>> transport_generic_free_cmd twice. It looks like it works ok, because your patch added the "cmd->se_lun = NULL"
>> in transport_lun_remove_cmd, so we won't do a double list deletion.
>> It feels dirty though. I can feel Bart saying, "Mike did you see the
>> comment at the top of the function". :)
>>
>> Maybe it's best to more cleanly unwind what was setup in the rror
>> path. I think we can fix lun_ref leak too.
>>
>> So instead of doing transport_generic_free_cmd above do
>> transport_lun_remove_cmd to match/undo the transport_lookup_tmr_lun call in iscsit_handle_task_mgt_cmd?
>
>Shoot. I'm all over the place. I think the root issue is my original comment on the v1 patch was wrong.
>On a failure we would still do:
>iscsit_free_cmd -> transport_generic_free_cmd -> transport_lun_remove_cmd
>right? So we don't need any change in the iscsi target. It should all just work.
iscsit_free_cmd will be called only at response completion(next incoming iscsi command): iscsit_ack_from_expstatsn -> iscsit_free_cmd.
That produces some unacceptable delay of lun unlinking from cmd. There is a bug report to the similar behavior:
http://lkml.iu.edu/hypermail/linux/kernel/2002.0/05272.html
Because of that complain, the commit 83f85b8ec305, that solves the same crash as I am fixing, was reverted.
So, this piece of patch has some indirect relation :)
I will extract it to a separate patch in the coming patchset on TMF handling.
BR,
Dmitry
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2021-04-21 15:07 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-04-16 9:21 [PATCH v2] target: core: remove from tmr_list at lun unlink Dmitry Bogdanov
2021-04-16 21:38 ` Mike Christie
2021-04-16 21:41 ` Mike Christie
2021-04-16 22:39 ` Mike Christie
2021-04-16 22:50 ` Mike Christie
2021-04-21 15:07 ` Dmitriy Bogdanov
2021-04-17 9:39 ` Konstantin Shelekhin
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