Hello, James.
This is repost of reqfn-reimplmentation patchset posted about a month
ago. As REQ_SPECIAL semantics patchset, which this patchset depends
on, has been accepted with slight modification (REQ_SOFTBARRIER
handled by blk layer), this patchset is adjusted accordingly. Also,
it's updated to use original scsi_add_timer function as timer API
change patch isn't accepted yet.
scsi_reqfn_reimplementation patch depends on the timer update
patchset I've posted yesterday. The only dependency is the removal of
scsi_dispatch_cmd() because the timer patchset modifies
scsi_queue_insert() call in that function. If you decide to not
accept the timer updates, just removing scsi_cmd_get_serial() and
scsi_dispatch_cmd() by hand should suffice.
Original description follows.
This patchset reimplements scsi_request_fn(). All prep's are moved
into prep_fn and all state checking/issueing are moved into
scsi_reqfn. prep_fn() only terminates/defers unpreparable requests
and all requests are terminated through scsi midlayer.
[ Start of patch descriptions ]
01_scsi_reqfn_consolidate_error_handling.patch
: consolidate error handling out of scsi_init_io() into scsi_prep_fn()
This patch fixes a queue stall bug which occurred when sgtable
allocation failed and device_busy == 0. When scsi_init_io()
returns BLKPREP_DEFER or BLKPREP_KILL, it's supposed to free
resources itself. This patch consolidates defer and kill
handling into scsi_prep_fn().
Note that this patch doesn't consolidate state defer/kill
handlings in scsi_prep_fn() as all state checks will be moved
into scsi_reques_fn() by the following reqfn_reimpl patch.
ret value checking was changed to switch() as in James's
patch. Also, kill: comment is copied from James's patch.
02_scsi_reqfn_move_preps_to_prep_fn.patch
: move request preps in other places into prep_fn()
Move request preparations scattered in scsi_request_fn() and
scsi_dispatch_cmd() into scsi_prep_fn()
* CDB_SIZE check in scsi_dispatch_cmd()
* SCSI-2 LUN preparation in scsi_dispatch_cmd()
No invalid request reaches scsi_request_fn() anymore.
Note that scsi_init_cmd_errh() is still left in
scsi_request_fn(). As all requeued requests need its sense
buffer and result value cleared, we can't move this to
prep_fn() yet. This is moved into prep_fn in the following
requeue path consoildation patchset.
03_scsi_reqfn_reimplementation.patch
: reimplement scsi_request_fn()
New scsi_request_fn() is formatted mostly as Chistoph Hellwig
suggested.
This patch rewrites scsi_request_fn(). scsi_dispatch_cmd() is
merged into scsi_request_fn(). Goals are
* Remove unnecessary operations (host_lock unlocking/locking,
recursing into scsi_run_queue(), ...)
* Consolidate defer/kill paths.
* Be concise.
The following bugs are fixed.
* All killed requests now get fully prep'ed and pass through
__scsi_done(). This is the only kill path.
- scsi_cmnd leak in offline-kill path removed
- unfinished request bug in
scsi_dispatch_cmd():SDEV_DEL-kill path removed.
- commands are never terminated directly from blk
layer unless they are invalid, so no need to supply
req->end_io callback for special requests.
* Timer is added while holding host_lock, after all conditions
are checked and serial number is assigned. This guarantees
that until host_lock is released, the scsi_cmnd pointed to
by cmd isn't released. That didn't hold in the original
code and, theoretically, the original code could access
already released cmd.
* For the same reason, if shost->hostt->queuecommand() fails,
we try to delete the timer before releasing host_lock.
Other changes/notes
* host_lock is acquired and released only once.
enter (qlocked) -> enter loop -> dev-prep -> switch to hlock -\
^---- switch to qlock <- issue <- host-prep <-/
* unnecessary if () on get_device() removed.
* loop on elv_next_request() instead of blk_queue_plugged().
We now explicitly break out of loop when we plug and check if
the queue has been plugged underneath us at the end of loop.
* All device/host state checks are done in this function and
done only once while holding qlock/host_lock respectively.
* Requests which get deferred during dev-prep are never
removed from request queue, so deferring is achieved by
simply breaking out of the loop and returning.
* Failure of blk_queue_start_tag() on tagged queue is a BUG
now. This condition should have been catched by
scsi_dev_queue_ready().
* req->special == NULL test removed. This just can't happen,
and even if it ever happens, scsi_request_fn() will
deterministically oops.
* Requests which gets deferred during host-prep are requeued
using blk_requeue_request(). This is the only requeue path.
04_scsi_reqfn_remove_wait_req_end_io.patch
: remove unnecessary scsi_wait_req_end_io()
As all requests are now terminated via scsi midlayer, we don't
need to set end_io for special reqs, remove it.
[ End of patch descriptions ]
Thanks a lot.
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