Please ignore this patch. Subject line is messed up. I am going to resend with subject line fixed. > -----Original Message----- > From: linux-scsi-owner@xxxxxxxxxxxxxxx [mailto:linux-scsi- > owner@xxxxxxxxxxxxxxx] On Behalf Of Kashyap, Desai > Sent: Wednesday, May 04, 2011 4:34 PM > To: linux-scsi@xxxxxxxxxxxxxxx > Cc: James.Bottomley@xxxxxxxxxxxxxxxxxxxxx; Moore, Eric; Prakash, Sathya > Subject: [PATCH 1/3] mpt2sas: removetheuseofwriteq@xxxxxxx, since > writeq is not atomic > > > 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 > static inline void _base_writeq(__u64 b, volatile void __iomem *addr, > spinlock_t *writeq_lock) > { > @@ -1570,13 +1569,6 @@ static inline void _base_writeq(__u64 b, > volatile void __iomem *addr, > writel((u32)(data_out >> 32), (addr + 4)); > spin_unlock_irqrestore(writeq_lock, flags); > } > -#else > -static inline void _base_writeq(__u64 b, volatile void __iomem *addr, > - spinlock_t *writeq_lock) > -{ > - writeq(cpu_to_le64(b), addr); > -} > -#endif > > /** > * mpt2sas_base_put_smid_scsi_io - send SCSI_IO request to firmware > -- > 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 -- 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
