Re: [PATCH] scsi: ata: Fix a race condition between scsi error handler and ahci interrupt

[Li Nan <linan666@xxxxxxxxxxxxxxx>]

在 2023/8/22 18:30, Niklas Cassel 写道:
> On Tue, Aug 22, 2023 at 05:20:33PM +0800, Li Nan wrote:
> > Thanks for your reply, Niklas.
> >
> > 在 2023/8/21 21:51, Niklas Cassel 写道:
> > > On Thu, Aug 10, 2023 at 09:48:48AM +0800, linan666@xxxxxxxxxxxxxxx wrote:
> >
> > [snip]
> >
> > > Hello Li Nan,
> > >
> > > I do not understand why the code in:
> > > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L722-L731
> > >
> > > does not kick in, and repeats EH.
> > >
> > >
> > > EH_PENDING is cleared before ->error_handler() is called:
> > > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L697
> > >
> > > So ahci_error_intr() from the second error interrupt, which is called after
> > > thawing the port, should have called ata_std_sched_eh(), which calls
> > > ata_eh_set_pending(), which should have set EH_PENDING:
> > > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L884
> > >
> > >
> > >
> > > My only guess is that after thawing the port:
> > > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L2807
> > >
> > > The second error irq comes, and sets EH_PENDING,
> > > but then this silly code might clear it:
> > > https://github.com/torvalds/linux/blob/v6.5-rc7/drivers/ata/libata-eh.c#L2825-L2837
> >
> > Yeah, I think so.
> >
> > > I think the best way would be if we could improve this "spurious error
> > > condition check"... because if this is indeed the code that clears EH_PENDING
> > > for you, then this code basically makes the "goto repeat" code in
> > > ata_scsi_port_error_handler() useless...
> > >
> > >
> > > An alternative to improving the "spurious error condition check" might be for
> > > you to try something like:
> >
> > We have used this solution before, but it will case WARN_ON in
> > ata_eh_finish() as below:
> >
> >    WARNING: CPU: 1 PID: 118 at ../drivers/ata/libata-eh.c:4016
> > ata_eh_finish+0x15a/0x170
>
> Ok.
>
> How about if you simply move the WARN_ON to ata_scsi_port_error_handler()
> as well:
>
> diff --git a/drivers/ata/libata-eh.c b/drivers/ata/libata-eh.c
> index 35e03679b0bf..5be2fc651131 100644
> --- a/drivers/ata/libata-eh.c
> +++ b/drivers/ata/libata-eh.c
> @@ -741,6 +741,12 @@ void ata_scsi_port_error_handler(struct Scsi_Host *host, struct ata_port *ap)
>                   */
>                  ap->ops->end_eh(ap);
>   
> +               if (!ap->scsi_host->host_eh_scheduled) {
> +                       /* make sure nr_active_links is zero after EH */
> +                       WARN_ON(ap->nr_active_links);
> +                       ap->nr_active_links = 0;
> +               }
> +
>                  spin_unlock_irqrestore(ap->lock, flags);
>                  ata_eh_release(ap);
>          } else {
> @@ -962,7 +968,7 @@ void ata_std_end_eh(struct ata_port *ap)
>   {
>          struct Scsi_Host *host = ap->scsi_host;
>   
> -       host->host_eh_scheduled = 0;
> +       host->host_eh_scheduled--;
>   }
>   EXPORT_SYMBOL(ata_std_end_eh);
>   
> @@ -3948,10 +3954,6 @@ void ata_eh_finish(struct ata_port *ap)
>                          }
>                  }
>          }
> -
> -       /* make sure nr_active_links is zero after EH */
> -       WARN_ON(ap->nr_active_links);
> -       ap->nr_active_links = 0;
>   }
>   
>   /**
>
>
>
> Kind regards,
> Niklas

We have tested this patch and it can fix the bug. Thank you so much. :)

Feel free to add:

Tested-by: Li Nan <linan122@xxxxxxxxxx>

--
Thanks,
Nan