On Wed, May 18, 2011 at 09:37:08AM +0530, Desai, Kashyap wrote:
> On Wed, 2011-05-04 at 17:23 +0530, Kashyap, Desai wrote:
> > The following code seems to be there in /usr/src/linux/arch/x86/include/asm/io.h.
> > This is not going to work.
> >
> > static inline void writeq(__u64 val, volatile void __iomem *addr)
> > {
> > writel(val, addr);
> > writel(val >> 32, addr+4);
> > }
> >
> > So with this code turned on in the kernel, there is going to be race condition
> > where multiple cpus can be writing to the request descriptor at the same time.
> >
> > Meaning this could happen:
> > (A) CPU A doest 32bit write
> > (B) CPU B does 32 bit write
> > (C) CPU A does 32 bit write
> > (D) CPU B does 32 bit write
> >
> > We need the 64 bit completed in one access pci memory write, else spin lock is required.
> > Since it's going to be difficult to know which writeq was implemented in the kernel,
> > the driver is going to have to always acquire a spin lock each time we do 64bit write.
> >
> > Cc: stable@xxxxxxxxxx
> > Signed-off-by: Kashyap Desai <kashyap.desai@xxxxxxx>
> > ---
> > diff --git a/drivers/scsi/mpt2sas/mpt2sas_base.c b/drivers/scsi/mpt2sas/mpt2sas_base.c
> > index efa0255..5778334 100644
> > --- a/drivers/scsi/mpt2sas/mpt2sas_base.c
> > +++ b/drivers/scsi/mpt2sas/mpt2sas_base.c
> > @@ -1558,7 +1558,6 @@ mpt2sas_base_free_smid(struct MPT2SAS_ADAPTER *ioc, u16 smid)
> > * care of 32 bit environment where its not quarenteed to send the entire word
> > * in one transfer.
> > */
> > -#ifndef writeq
>
> Why not make this #ifndef CONFIG_64BIT? You know that all 64 bit
> systems have writeq implemented correctly; you suspect 32 bit systems
> don't.
>
> James
>
> James, This issue was observed on PPC64 system. So what you have suggested will not solve this issue.
> If we are sure that writeq() is atomic across all architecture, we can use it safely. As we have seen issue on ppc64, we are not confident to use
> "writeq" call.
So have you told the powerpc people that they have a broken writeq?
And why do you obfuscate your report by talking about i386 when it's
really about powerpc64?
--
Matthew Wilcox Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours. We can't possibly take such
a retrograde step."
--
To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
