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

[Li Nan]

在 2023/9/4 19:57, Niklas Cassel 写道:
> On Mon, Sep 04, 2023 at 07:45:51PM +0800, Li Nan wrote:
> > 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. :)
>
> Awesome! :)
>
> Please send out a real patch, so that it is easier for the maintainer to
> apply.
>
> No need to give any credit to me.
>
>
> Kind regards,
> Niklas

It is my pleasure. I will send v2 later.

--
Thanks,
Nan