On 3/30/19 10:38 AM, zhengbin (A) wrote:
> ping
>
> On 2019/3/26 21:29, zhengbin (A) wrote:
>> On 2019/3/25 19:55, zhengbin (A) wrote:
>>> On 2019/3/25 18:02, Pavel Tikhomirov wrote:
>>>> Likely we should do the same for host_eh_scheduled++ as we do for
>>>> host_failed++ in scsi_eh_inc_host_failed. Just put it in call_rcu. These
>>>> way rcu_read_lock would be enough: if we don't see RECOVERY state in
>>>> scsi_dec_host_busy, that means that host_eh_scheduled++ and
>>>> corresponding scsi_eh_wakeup not yet happened, and they will handle
>>>> wakeup for us.
>>>>
>>>> Bart did these rcu-way to make common path faster, so better we do it
>>>> without slow mem-barrier.
>> Bart did these rcu-way, and protecting the host_failed checks with the SCSI host lock.
>> If we use rcu-way, maybe we need to put host_busy & shost_state in host_lock too.
>> I think we should use smp_mb().
I'm not staying against using barrier(or spinlock implicit one).
Actually I still use my old 'slow' spinlock fix because it is much simpler.
>>
>> Looking forward to reply, thanks.
>>> If we use rcu for host_eh_scheduled. we should add rcu_head in Scsi_Host,
>>> replace scsi_schedule_eh(ap->scsi_host) with call_rcu in ata_std_sched_eh, sas_queue_reset??
>>> This will trigger a kernel hang or oops because of double or more call_rcu() call.
I'm not an expert in rcu but if double rcu warning is a protection from
leaking resources like double free, and as we don't free anything from
our rcu callback, double calling it might be fine.
>>>
>>> Any more suggestions?>>
>>>> On 3/25/19 12:05 PM, zhengbin wrote:
>>>>> When I use fio test kernel in the following steps:
>>>>> 1.The sas controller mixes SAS/SATA disks
>>>>> 2.Use fio test all disks
>>>>> 3.Simultaneous enable/disable/link_reset/hard_reset PHY
>>>>>
>>>>> it will hung in ata_port_wait_eh
>>>>> Call trace:
>>>>> __switch_to+0xb4/0x1b8
>>>>> __schedule+0x1e8/0x718
>>>>> schedule+0x38/0x90
>>>>> ata_port_wait_eh+0x70/0xf8
>>>>> sas_ata_wait_eh+0x24/0x30 [libsas]
>>>>> transport_sas_phy_reset.isra.3+0x128/0x160 [libsas]
>>>>> phy_reset_work+0x20/0x30 [libsas]
>>>>> process_one_work+0x1e4/0x460
>>>>> worker_thread+0x40/0x450
>>>>> kthread+0x12c/0x130
>>>>> ret_from_fork+0x10/0x18
>>>>>
>>>>> The key code process is like this:
>>>>> scsi_dec_host_busy
>>>>> atomic_dec(&shost->host_busy);
>>>>> if (unlikely(scsi_host_in_recovery(shost))) {
>>>>> spin_lock_irqsave(shost->host_lock, flags);
>>>>> ...
>>>>> scsi_eh_wakeup(shost)
>>>>> ...
>>>>> }
>>>>>
>>>>> scsi_schedule_eh
>>>>> spin_lock_irqsave(shost->host_lock, flags);
>>>>> if (scsi_host_set_state(shost, SHOST_RECOVERY) == 0 ||
>>>>> scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY) == 0) {
>>>>> ...
>>>>> scsi_eh_wakeup(shost);
>>>>> }
>>>>>
>>>>> scsi_eh_wakeup
>>>>> if (scsi_host_busy(shost) == shost->host_failed)
>>>>> wake_up_process(shost->ehandler);
>>>>>
>>>>> In scsi_dec_host_busy, host_busy & shost_state not in spinlock. Neither
>>>>> function wakes up the SCSI error handler in the following timing:
>>>>>
>>>>> CPU 0(call scsi_dec_host_busy) CPU 1(call scsi_schedule_eh)
>>>>> LOAD shost_state(!=recovery)
>>>>> scsi_host_set_state(SHOST_RECOVERY)
>>>>> scsi_eh_wakeup(host_busy != host_failed)
>>>>> atomic_dec(&shost->host_busy);
>>>>> if (scsi_host_in_recovery(shost))
>>>>>
>>>>> Add a smp_mb between host_busy and shost_state.
>>>>>
>>>>> Signed-off-by: zhengbin <zhengbin13@xxxxxxxxxx>
>>>>> ---
>>>>> drivers/scsi/scsi_error.c | 7 +++++++
>>>>> drivers/scsi/scsi_lib.c | 5 +++++
>>>>> 2 files changed, 12 insertions(+)
>>>>>
>>>>> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
>>>>> index 1b8378f..c605a71 100644
>>>>> --- a/drivers/scsi/scsi_error.c
>>>>> +++ b/drivers/scsi/scsi_error.c
>>>>> @@ -88,6 +88,13 @@ void scsi_schedule_eh(struct Scsi_Host *shost)
>>>>>
>>>>> if (scsi_host_set_state(shost, SHOST_RECOVERY) == 0 ||
>>>>> scsi_host_set_state(shost, SHOST_CANCEL_RECOVERY) == 0) {
>>>>> + /*
>>>>> + * We have to order shost_state store above and test of
>>>>> + * the host_busy(scsi_eh_wakeup will test it), because
>>>>> + * scsi_dec_host_busy accesses these variables without
>>>>> + * host_lock.
>>>>> + */
>>>>> + smp_mb();
>>>>> shost->host_eh_scheduled++;
>>>>> scsi_eh_wakeup(shost);
>>>>> }
>>>>> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
>>>>> index 601b9f1..9094d20 100644
>>>>> --- a/drivers/scsi/scsi_lib.c
>>>>> +++ b/drivers/scsi/scsi_lib.c
>>>>> @@ -337,6 +337,11 @@ static void scsi_dec_host_busy(struct Scsi_Host *shost)
>>>>>
>>>>> rcu_read_lock();
>>>>> atomic_dec(&shost->host_busy);
>>>>> + /*
>>>>> + * We have to order host_busy dec above and test of the shost_state
>>>>> + * below outside the host_lock.
>>>>> + */
>>>>> + smp_mb();
>>>>> if (unlikely(scsi_host_in_recovery(shost))) {
>>>>> spin_lock_irqsave(shost->host_lock, flags);
>>>>> if (shost->host_failed || shost->host_eh_scheduled)
>>>>> --
>>>>> 2.7.4
>>>>>
>>>>
>
--
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.
