Re: [PATCH 4/7] megaraid_sas: Send SYNCHRONIZE_CACHE command to firmware

[James Bottomley <jejb@linux.vnet.ibm.com>]

On Mon, 2016-10-17 at 12:27 -0400, Ric Wheeler wrote:
> On 10/17/2016 12:20 PM, James Bottomley wrote:
> > On Mon, 2016-10-17 at 09:01 -0400, Ric Wheeler wrote:
> > > On 10/17/2016 07:34 AM, Hannes Reinecke wrote:
> > > > On 10/17/2016 12:24 PM, Sumit Saxena wrote:
> > > > > megaraid_sas driver returns SYNCHRONIZE_CACHE command back to
> > > > > SCSI layer without sending it to firmware as firmware takes
> > > > > care
> > > > > of flushing cache.  This patch will change the driver
> > > > > behavior
> > > > > wrt SYNCHRONIZE_CACHE handling. If underlying firmware has
> > > > > support to handle the SYNCHORNIZE_CACHE, driver will send it
> > > > > for
> > > > > firmware otherwise complete it back to SCSI layer with
> > > > > SUCCESS
> > > > > immediately.  If  Firmware  handle SYNCHORNIZE_CACHE for both
> > > > > VD
> > > > > and JBOD "canHandleSyncCache" bit in scratch pad
> > > > > register(offset
> > > > > 0x00B4) will be set.
> > > > > 
> > > > > This behavior can be controlled via module parameter and user
> > > > > can
> > > > > fallback to old behavior of returning SYNCHRONIZE_CACHE by
> > > > > driver
> > > > > only without sending it to firmware.
> > > > > 
> > > > > Signed-off-by: Sumit Saxena <sumit.saxena@broadcom.com>
> > > > > Signed-off-by: Kashyap Desai <kashyap.desai@broadcom.com>
> > > > > ---
> > > > >    drivers/scsi/megaraid/megaraid_sas.h        |  3 +++
> > > > >    drivers/scsi/megaraid/megaraid_sas_base.c   | 14 ++++++---
> > > > > -----
> > > > >    drivers/scsi/megaraid/megaraid_sas_fusion.c |  3 +++
> > > > >    drivers/scsi/megaraid/megaraid_sas_fusion.h |  2 ++
> > > > >    4 files changed, 14 insertions(+), 8 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/scsi/megaraid/megaraid_sas.h
> > > > > b/drivers/scsi/megaraid/megaraid_sas.h
> > > > > index ca86c88..43fd14f 100644
> > > > > --- a/drivers/scsi/megaraid/megaraid_sas.h
> > > > > +++ b/drivers/scsi/megaraid/megaraid_sas.h
> > > > > @@ -1429,6 +1429,8 @@ enum FW_BOOT_CONTEXT {
> > > > >    #define MR_MAX_REPLY_QUEUES_EXT_OFFSET_SHIFT    14
> > > > >    #define MR_MAX_MSIX_REG_ARRAY                   16
> > > > >    #define MR_RDPQ_MODE_OFFSET			0X00800
> > > > > 000
> > > > > +#define MR_CAN_HANDLE_SYNC_CACHE_OFFSET		0X010
> > > > > 0000
> > > > > 0
> > > > > +
> > > > >    /*
> > > > >    * register set for both 1068 and 1078 controllers
> > > > >    * structure extended for 1078 registers
> > > > > @@ -2140,6 +2142,7 @@ struct megasas_instance {
> > > > >    	u8 is_imr;
> > > > >    	u8 is_rdpq;
> > > > >    	bool dev_handle;
> > > > > +	bool fw_sync_cache_support;
> > > > >    };
> > > > >    struct MR_LD_VF_MAP {
> > > > >    	u32 size;
> > > > > diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c
> > > > > b/drivers/scsi/megaraid/megaraid_sas_base.c
> > > > > index 092387f..a4a8e2f 100644
> > > > > --- a/drivers/scsi/megaraid/megaraid_sas_base.c
> > > > > +++ b/drivers/scsi/megaraid/megaraid_sas_base.c
> > > > > @@ -104,6 +104,10 @@ unsigned int scmd_timeout =
> > > > > MEGASAS_DEFAULT_CMD_TIMEOUT;
> > > > >    module_param(scmd_timeout, int, S_IRUGO);
> > > > >    MODULE_PARM_DESC(scmd_timeout, "scsi command timeout (10
> > > > > -90s),
> > > > > default 90s. See megasas_reset_timer.");
> > > > >    
> > > > > +bool block_sync_cache;
> > > > > +module_param(block_sync_cache, bool, S_IRUGO);
> > > > > +MODULE_PARM_DESC(block_sync_cache, "Block SYNC CACHE by
> > > > > driver
> > > > > Default: 0(Send it to firmware)");
> > > > > +
> > > > >    MODULE_LICENSE("GPL");
> > > > >    MODULE_VERSION(MEGASAS_VERSION);
> > > > >    MODULE_AUTHOR("megaraidlinux.pdl@avagotech.com");
> > > > > @@ -1700,16 +1704,10 @@ megasas_queue_command(struct
> > > > > Scsi_Host
> > > > > *shost, struct scsi_cmnd *scmd)
> > > > >    		goto out_done;
> > > > >    	}
> > > > >    
> > > > > -	switch (scmd->cmnd[0]) {
> > > > > -	case SYNCHRONIZE_CACHE:
> > > > > -		/*
> > > > > -		 * FW takes care of flush cache on its own
> > > > > -		 * No need to send it down
> > > > > -		 */
> > > > > +	if ((scmd->cmnd[0] == SYNCHRONIZE_CACHE) &&
> > > > > +		(!instance->fw_sync_cache_support)) {
> > > > >    		scmd->result = DID_OK << 16;
> > > > >    		goto out_done;
> > > > > -	default:
> > > > > -		break;
> > > > >    	}
> > > > >    
> > > > >    	return instance->instancet
> > > > > ->build_and_issue_cmd(instance, scmd);
> > > > > diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.c
> > > > > b/drivers/scsi/megaraid/megaraid_sas_fusion.c
> > > > > index 2159f6a..8237580 100644
> > > > > --- a/drivers/scsi/megaraid/megaraid_sas_fusion.c
> > > > > +++ b/drivers/scsi/megaraid/megaraid_sas_fusion.c
> > > > > @@ -747,6 +747,9 @@ megasas_ioc_init_fusion(struct
> > > > > megasas_instance *instance)
> > > > >    		ret = 1;
> > > > >    		goto fail_fw_init;
> > > > >    	}
> > > > > +	if (!block_sync_cache)
> > > > > +		instance->fw_sync_cache_support =
> > > > > (scratch_pad_2
> > > > > &
> > > > > +			MR_CAN_HANDLE_SYNC_CACHE_OFFSET) ? 1
> > > > > :
> > > > > 0;
> > > > >    
> > > > >    	IOCInitMessage =
> > > > >    	  dma_alloc_coherent(&instance->pdev->dev,
> > > > > diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.h
> > > > > b/drivers/scsi/megaraid/megaraid_sas_fusion.h
> > > > > index e3bee04..2857154 100644
> > > > > --- a/drivers/scsi/megaraid/megaraid_sas_fusion.h
> > > > > +++ b/drivers/scsi/megaraid/megaraid_sas_fusion.h
> > > > > @@ -72,6 +72,8 @@
> > > > >    #define MPI2_SUP_REPLY_POST_HOST_INDEX_OFFSET  
> > > > >  (0x0000030C)
> > > > >    #define MPI2_REPLY_POST_HOST_INDEX_OFFSET	(0x000000
> > > > > 6C)
> > > > >    
> > > > > +extern bool block_sync_cache;
> > > > > +
> > > > >    /*
> > > > >     * Raid context flags
> > > > >     */
> > > > > 
> > > > Be extra careful with that.
> > > > 
> > > > SYNCHRONIZE_CACHE has (potentially) a global scope, as there
> > > > might
> > > > be an array-wide cache, and a cache flush would affect the
> > > > entire
> > > > cache. Linux is using SYNCHRONIZE_CACHE as a per device
> > > > setting, ie
> > > > it assumes that the effects of a cache flush is restricted to
> > > > the
> > > > device in question.
> > > > 
> > > > If this is _not_ the case I'd rather not enable it.
> > > > Have you checked that enabling this functionality doesn't have
> > > > negative performance impact?
> > > > 
> > > > Cheers,
> > > > 
> > > > Hannes
> > > This must go in - without this fix, there is no data integrity
> > > for
> > > any file system.
> > That's not what I get from the change log.  What it says to me is 
> > that the caches are currently firmware managed.  Barring firmware 
> > bugs, that means that we currently don't have any integrity issues.
> 
> Your understanding (or the change log) is incorrect.

There's no current way in English of construing "as firmware takes care
of flushing cache" to mean its inverse, so the changelog needs updating
to explain that firmware does *not* take care of cache flushing, so
effectively nothing does and we'll need a cc to stable if the problem
is that nothing takes care of flushing the drive caches.

James


> The issue here is for devices that are non-RAID or pass through - 
> this is a real issue and has been seen in practice.