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

[Robert Hancock <hancockr@shaw.ca>]

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@nvidia.com
> 
> ---
>  
> 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.

Is there a reason why going into register mode should cause a lockup in 
this case?