Re: [PATCH] sata_nv: fix nmi intr or system hanging in rhel4u6 adma.

[Jeff Garzik]

Robert Hancock wrote:
> Kuan Luo wrote:
> > Hi, robert
> > One customer reported that their system received a nmi interrupt after
> > issuing "dd if=/dev/sdb of=/dev/null" on a defective disk in rhel4u6.
> > I tested it and found  that my system hung both in rhel4u6(2.6.9-67) and
> > 2.6.24-rc7.
> > The patch can work well,  but I am not sure if the patch has other
> > potential effect on adma.
> > I attached a  file in case of lines breaked.
> >
> > The below info comes from Gunther Mayer to reproduce the issue.
> > "
> > used a Seagate ST3500841NS 3.AE for my test; probably other seagate 
> > drives are also capable of creating media errors with the new hdparm-8.1:
> > - compile hdparm-8.1 - hdparm -- yes-i-know-what-i-am-doing 
> > --make-bad-sector 60000 /dev/sdb
> > Unfortunately this does not succeed for nvidia sata controller (timeouts
> > et al.), but it worked fine on AHCI machine (e.g. FSC R640).
> > When I insert this newly created defective disk in Ultra 20, it 
> > reboots within seconds after issueing "dd if=/dev/sdb of=/dev/null". "
> >
> > Signed-off-by: kluo@xxxxxxxxxx
> >
> > ---
> >  
> > drivers/ata/sata_nv.c |    5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/ata/sata_nv.c b/drivers/ata/sata_nv.c
> > index ed5473b..e824260 100644
> > --- a/drivers/ata/sata_nv.c
> > +++ b/drivers/ata/sata_nv.c
> > @@ -837,9 +837,10 @@ static void nv_adma_tf_read(struct ata_port *ap,
> > struct ata_taskfile *tf)
> >         all shortly be aborted anyway. We assume that NCQ commands
> > are not
> >         issued via passthrough, which is the only way that switching
> > into
> >         ADMA mode could abort outstanding commands. */
> > -    nv_adma_register_mode(ap);
> > +    struct nv_adma_port_priv *pp = ap->private_data;
> >  
> > -    ata_tf_read(ap, tf);
> > +    if (pp->flags & NV_ADMA_PORT_REGISTER_MODE)
> > +        ata_tf_read(ap, tf);
> >  }
> >  
> >  static unsigned int nv_adma_tf_to_cpb(struct ata_taskfile *tf, __le16
> > *cpb)
>
> This is basically avoiding switching into register mode, right? I don't 
> think this is a very good solution as the point of the tf_read function 
> is that it's supposed to read the taskfile provided by the drive to 
> diagnose the error, so not doing this isn't a good thing.

Agree with this analysis -- if ->tf_read() is being called, then 
obviously the core wants a current copy of the device's ATA registers.

It is not a good solution to simply avoiding returning meaningful data, 
because -- as Robert notes -- we need tf_read for analysis.

	Jeff



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