Re: Patch added to scsi-rc-fixes-2.6: [SCSI] host lock push-down

From: Jeff Garzik
Date: Wed Nov 10 2010 - 18:28:18 EST


On 11/10/2010 05:40 PM, James Bottomley wrote:
Your commit:

[SCSI] host lock push-down

Move the mid-layer's ->queuecommand() invocation from being locked
with the host lock to being unlocked to facilitate speeding up the
critical path for drivers who don't need this lock taken anyway.

The patch below presents a simple SCSI host lock push-down as an
equivalent transformation. No locking or other behavior should change
with this patch. All existing bugs and locking orders are preserved.

Minimal code disturbance was attempted with this change. Most drivers
needed only two one-line modifications for their host lock push-down.

Signed-off-by: Jeff Garzik<jgarzik@xxxxxxxxxx>
Signed-off-by: James Bottomley<James.Bottomley@xxxxxxx>

has been added to the upstream SCSI tree
You can find it here:

No comments on renaming ->queuecommand to something else?

The consequences are rather dire if this goes unnoticed, yes?

Jeff


In http://marc.info/?l=linux-ide&m=128891665713984&w=2 I wrote:
An alternate arrangement, not presented by this patch, might
be preferred: in order to make it clear that queuecommand
locking has changed, one could s/queuecommand/queuecommand_nl/ in
Scsi_Host_Template, in order to guarantee that drivers are either
(a) upgraded or (b) broken at compile time. Compile-time detection of
new locking may be desirable, and I'll volunteer to change my patch to
do that, if community members prefer that route instead of below.

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