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.
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 <[email protected]>
> ---
> 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.
