Hello, James.
This patchset is split up of REQ_SPECIAL update patches (#01-02) of
previous patchset posted on March 31. Explicit setting of
REQ_SOFTBARRIER in scsi_init_io() is added.
This patchset makes REQ_SPECIAL mean that the request is a special
request and REQ_SOFTBARRIER setting explicit.
Previously, REQ_SPECIAL duplicately meant the request has been
prepp'ed by SCSI midlayer and/or the request is a special request.
This left special requests handling in the midlayer subtley
inconsistent.
Also, the setting of REQ_SPECIAL was done by the block layer using
blk_insert_request() mostly but sometimes by the SCSI midlayer (when
returning BLK_PREP_DEFER from scsi_prep_fn()). blk_insert_request()
was used for two different purposes.
* enqueue special requests
* turn on REQ_SPECIAL|REQ_SOFTBARRIER and call blk_requeue_request().
The second somewhat unobvious feature of blk_insert_request() is used
only by SCSI midlayer and SCSI midlayer depended on it to set
REQ_SOFTBARRIER. Unfortunately, when the SCSI midlayer sets
REQ_SPECIAL explicitly (sg allocation failure path) it didn't set
REQ_SOFTBARRIER, creating a *highly* unlikely but still existing dead
lock condition caused by allowing reorder of a request which has its
cmd allocated. IMHO, this proves the subtlety of current situation.
This patch makes SCSI midlayer use blk_requeue_request() for
reqeueuing and setting of REQ_SOFTBARRIER explicit.
To prevent more misuses, the last patch in this patchset remove
requeue feature from blk_insert_request(). Requeueing should be done
with blk_requeue_request() not blk_insert_request().
[ Start of patch descriptions ]
01_scsi_REQ_SPECIAL_semantic_scsi_init_io.patch
: replace REQ_SPECIAL with REQ_SOFTBARRIER in scsi_init_io()
scsi_init_io() used to set REQ_SPECIAL when it fails sg
allocation before requeueing the request by returning
BLKPREP_DEFER. REQ_SPECIAL is being updated to mean special
requests and we need to set REQ_SOFTBARRIER for half-prepp'ed
requests. So, replace REQ_SPECIAL with REQ_SOFTBARRIER.
02_scsi_REQ_SPECIAL_semantic_scsi_queue_insert.patch
: make scsi_queue_insert() use blk_requeue_request()
scsi_queue_insert() used to use blk_insert_request() for
requeueing requests. This behavior depends on the unobvious
behavior of blk_insert_request() setting REQ_SPECIAL and
REQ_SOFTBARRIER when requeueing. This patch makes
scsi_queue_insert() use blk_requeue_request() and explicitly
set REQ_SOFTBARRIER. As REQ_SPECIAL now means special
requests, the flag is not set on requeue.
Note that scsi_queue_insert() now calls scsi_run_queue()
itself, and the prototype of the function is added right above
scsi_queue_insert(). This is temporary, as later requeue path
consolidation patchset removes scsi_queue_insert(). By adding
temporary prototype, we can do away with unnecessary changes.
03_scsi_REQ_SPECIAL_semantic_scsi_requeue_command.patch
: make scsi_requeue_request() use blk_requeue_request()
scsi_requeue_request() used to use blk_insert_request() for
requeueing requests. This behavior depends on the unobvious
behavior of blk_insert_request() setting REQ_SPECIAL and
REQ_SOFTBARRIER when requeueing. This patch makes
scsi_requeue_request() use blk_requeue_request() and
explicitly set REQ_SOFTBARRIER. As REQ_SPECIAL now means
special requests, the flag is not set on requeue.
04_scsi_blk_insert_request_no_requeue.patch
: remove requeue feature from blk_insert_request()
blk_insert_request() has a unobivous feature of requeuing a
request setting REQ_SPECIAL|REQ_SOFTBARRIER. SCSI midlayer
was the only user and as previous patches removed the usage,
remove the feature from blk_insert_request(). Only special
requests should be queued with blk_insert_request(). All
requeueing should go through blk_requeue_request().
[ End of patch descriptions ]
This patchset completes preparation for scsi_request_fn()
reimplementation patchset. As it seemed better to clear up requeue
paths inside scsi_request_fn() first, requeue path consolidation
patchset follows scsi_request_fn() reimplementation patchset.
Thanks a lot.
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