On 2019/3/25 20:20, John Garry wrote:
> On 25/03/2019 11:55, 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.
>
> Out of curiousity, which platform did you observe this on?
ARM64
>
> Thanks,
> John
>
>> 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.
>>
>> 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 <zhengbi...@huawei.com>
>>>> ---
>>>> 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
>>>>
>>>
>>
>>
>> .
>>
>
>
>
> .
>
