On 11/18/2010 05:57 PM, Nicholas A. Bellinger wrote:
<Trimming CC list>
On Thu, 2010-11-18 at 12:15 +0200, Boaz Harrosh wrote:
On 11/18/2010 12:19 AM, Nicholas A. Bellinger wrote:
From: Nicholas Bellinger<nab@xxxxxxxxxxxxxxx>
This patch converts the mpt2sas driver to run in host_lock less mode
with the new IRQ_DISABLE_SCSI_QCMD() that disables interrupts while
calling ->queuecommand() dispatch
Signed-off-by: Nicholas A. Bellinger<nab@xxxxxxxxxxxxxxx>
---
drivers/scsi/mpt2sas/mpt2sas_scsih.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/mpt2sas/mpt2sas_scsih.c b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
index 1a96a00..e564fe7 100644
--- a/drivers/scsi/mpt2sas/mpt2sas_scsih.c
+++ b/drivers/scsi/mpt2sas/mpt2sas_scsih.c
@@ -3304,7 +3304,7 @@ _scsih_eedp_error_handling(struct scsi_cmnd *scmd, u16 ioc_status)
}
/**
- * _scsih_qcmd - main scsi request entry point
+ * _scsih_qcmd_irq_disable - main scsi request entry point
* @scmd: pointer to scsi command object
* @done: function pointer to be invoked on completion
*
@@ -3315,7 +3315,7 @@ _scsih_eedp_error_handling(struct scsi_cmnd *scmd, u16 ioc_status)
* SCSI_MLQUEUE_HOST_BUSY if the entire host queue is full
*/
static int
-_scsih_qcmd_lck(struct scsi_cmnd *scmd, void (*done)(struct scsi_cmnd *))
+_scsih_qcmd_irq_disable(struct scsi_cmnd *scmd, void (*done)(struct scsi_cmnd *))
{
struct MPT2SAS_ADAPTER *ioc = shost_priv(scmd->device->host);
struct MPT2SAS_DEVICE *sas_device_priv_data;
@@ -3441,7 +3441,7 @@ _scsih_qcmd_lck(struct scsi_cmnd *scmd, void (*done)(struct scsi_cmnd *))
return SCSI_MLQUEUE_HOST_BUSY;
}
-static DEF_SCSI_QCMD(_scsih_qcmd)
+static IRQ_DISABLE_SCSI_QCMD(_scsih_qcmd)
How can this (and other in the patchset) can be correct? I mean I expect
that if you remove the lock,xx_qcmd_lck,unlock then inside the xx_qcmd_lck
there was an unlock,do123,lock and that driver was effectively running lockless
before. (like in iscsi). But here this is new behaviour. If it is correct
I would like to see a statement from you that:
"I have audited this driver, and all shared resources are protected by
XYZ so ..."
Otherwise how can I know this is correct? I have never audited this driver myself
So for this specific mpt2sas case, Vasu Dev had been testing the
lock_less case w/o disabling interrupts for his original
SHT->unlocked_qcmd=1 patch, and from his comments this mode was stable
during his JBOD lock_less small block IOP performance test.
Test results are not the same as reviewing and understanding the locking
in the driver, and adjusting the code accordingly...
_scsih_qcmd_lck() seems to rely on per-device and per-host data not
changing, which might seem to imply that the driver is secretly using
the SCSI host_lock to guarantee access to members such as
ioc->ioc_link_reset_in_progress or sas_target_priv_data->tm_busy.
These accesses appear racy in both lock-free and local_irq_save()
configurations from my naive reading, though I do see additional locking
inside mpt2sas_base_get_smid_scsiio()
Jeff
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