Hi Christof, Thanks for the response. I am running mkfs.ext3 command. I am doing the following in the driver for write(10): Queuecommand: sg = scsi_sglist(cmd->scsi_cmd); cmd->write_buf = (u8 *)(kmap_atomic(sg->page, KM_IRQ0) + sg->offset); Calculate checksum for write_buf Write Done: Calculate checksum for cmd->write_buf and checksums don't match. I am wondering how come OS changed the cmd->write_buf when I have not even unmapped the buffer. Is filesystem changing this cmd->write_buf pages when driver/HW is working on it? Is there anyway I can avoid this. How about if we allocate a local buffer(kmalloc/pci_alloc_consistent) and memcpy kmap_atomic to that local buffer and then calculate checksum on that local buffer. Will this help? --Anil --- On Thu, 9/9/10, Christof Schmitt <christof.schmitt@xxxxxxxxxx> wrote: > From: Christof Schmitt <christof.schmitt@xxxxxxxxxx> > Subject: Re: scsi_cmnd data_buffer checksum > To: "Anil kumar" <anils_r@xxxxxxxxx> > Cc: linux-kernel@xxxxxxxxxxxxxxx, linux-scsi@xxxxxxxxxxxxxxx > Date: Thursday, September 9, 2010, 4:00 AM > On Wed, Sep 08, 2010 at 08:36:32PM > -0700, Anil kumar wrote: > > > > I am writing a checksum calculation of scsi_cmnd data > buffer in the driver. > > > > I calculate the checksum of the scsi_cmd data > buffer(request_buffer) in driver queuecommand. > > > > Now when the command is completed from the hardware > and before driver sends it back to mid-layer, I calculate > the checksum again of the same scsi_cmd data_buffer again. > > > > Sometimes the checksums don't match. I mean somehow > looks like OS changed the scsi_cmd > data_buffer(request_buffer) in the meantime when driver is > working on the command. > > I print the address of the scsi_cmd data_buffer > (virtual address) and its same and the contents of the > buffer is also same during both the calculations. > > > > Can this happen? > > Yes. While a write I/O is being processed in Linux or in > flight, the > data buffers can change. This causes problems for other > checksums as > well; i ran into this when looking at the DIF/DIX checksums > for SCSI > commands. > > At the moment, this problem can be avoided e.g. by running > only direct > I/O on the xfs filesystem. There have been discussions > about this, a > short summary is here, look for "stable pages": > http://lwn.net/Articles/399148/ > > Christof > -- 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
