cfq-iosched: Fix null pointer dereference

NULL pointer dereference can happen in cfq_choose_cfqg()
when there are no cfq groups to select other than the
current serving group. Prevent this by adding a NULL
check before dereferencing.

Unable to handle kernel NULL pointer dereference at virtual address
[<c02502cc>] (cfq_dispatch_requests+0x368/0x8c0) from
[<c0243f30>] (blk_peek_request+0x220/0x25c)
[<c0243f30>] (blk_peek_request+0x220/0x25c) from
[<c0243f74>] (blk_fetch_request+0x8/0x1c)
[<c0243f74>] (blk_fetch_request+0x8/0x1c) from
[<c041cedc>] (mmc_queue_thread+0x58/0x120)
[<c041cedc>] (mmc_queue_thread+0x58/0x120) from
[<c00ad310>] (kthread+0x84/0x90)
[<c00ad310>] (kthread+0x84/0x90) from
[<c000eeac>] (kernel_thread_exit+0x0/0x8)

CRs-Fixed: 416466
Change-Id: I1fab93a4334b53e1d7c5dcc8f93cff174bae0d5e
Signed-off-by: Sujit Reddy Thumma <sthumma@codeaurora.org>
Signed-off-by: Seongmin Park <r_data@naver.com>
Added Simple I/O (SIO) scheduler.

Signed-off-by: Seongmin Park <r_data@naver.com>
Update Simple I/O Scheduler

Signed-off-by: Seongmin Park <r_data@naver.com>
Tune deadline for flash devices

Signed-off-by: Seongmin Park <r_data@naver.com>
block: deadline: disable front_merging.

Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: Seongmin Park <r_data@naver.com>
Add V(R) Scheduler

Conflicts:

	block/Kconfig.iosched
	block/Makefile

Conflicts:

	block/Kconfig.iosched
	block/Makefile

Signed-off-by: Seongmin Park <r_data@naver.com>
block: Adding ROW scheduling algorithm
Date	Thu, 1 Nov 2012 13:59:09 +0200

From: Tatyana Brokhman <tlinder@codeaurora.org>

This patch adds the implementation of a new scheduling algorithm - ROW.
The policy of this algorithm is to prioritize READ requests over WRITE
as much as possible without starving the WRITE requests.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:

	block/Makefile

Signed-off-by: Seongmin Park <r_data@naver.com>
row: Adding support for reinsert already dispatched req
Date	Tue, 11 Dec 2012 15:43:19 +0200

Add support for reinserting already dispatched request back to the
schedulers internal data structures.
The request will be reinserted back to the queue (head) it was
dispatched from as if it was never dispatched.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Seongmin Park <r_data@naver.com>
row: Add support for urgent request handling
Date	Tue, 11 Dec 2012 15:43:20 +0200

This patch add support for handling urgent requests.
ROW queue can be marked as "urgent". If an urgent queue was
un-served in a previous dispatch cycle and a request was added
to it - it will trigger issuing urgent request to the device driver.

Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Add some debug information on ROW queues

1. Add a counter for number of requests on queue.
2. Add function to print queues status (number requests
   currently on queue and number of already dispatched requests
   in current dispatch cycle).

Change-Id: I1e98b9ca33853e6e6a8ddc53240f6cd6981e6024
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Insert dispatch_quantum into struct row_queue

There is really no point in keeping the dispatch quantum
of a queue outside of it. By inserting it to the row_queue
structure we spare extra level in accessing it.

Change-Id: Ic77571818b643e71f9aafbb2ca93d0a92158b199
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:

	block/row-iosched.c

Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: fix sysfs functions - idle_time conversion

idle_time was updated to be stored in msec instead of jiffies.
So there is no need to convert the value when reading from user or
displaying the value to him.

Change-Id: I58e074b204e90a90536d32199ac668112966e9cf
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:

	block/row-iosched.c

Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Aggregate row_queue parameters to one structure

Each ROW queues has several parameters which default values are defined
in separate arrays. This patch aggregates all default values into one
array.
The values in question are:
 - is idling enabled for the queue
 - queue quantum
 - can the queue notify on urgent request

Change-Id: I3821b0a042542295069b340406a16b1000873ec6
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Dispatch requests according to their io-priority

This patch implements "application-hints" which is a way the issuing
application can notify the scheduler on the priority of its request.
This is done by setting the io-priority of the request.
This patch reuses an already existing mechanism of io-priorities developed
for CFQ. Please refer to kernel/Documentation/block/ioprio.txt for
usage example and explanations.

Change-Id: I228ec8e52161b424242bb7bb133418dc8b73925a
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:

	block/row-iosched.c

Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Idling mechanism re-factoring

At the moment idling in ROW is implemented by delayed work that uses
jiffies granularity which is not very accurate. This patch replaces
current idling mechanism implementation with hrtime API, which gives
nanosecond resolution (instead of jiffies).

Change-Id: I86c7b1776d035e1d81571894b300228c8b8f2d92
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:

	block/row-iosched.c

Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Don't notify URGENT if there are un-completed urgent req

When ROW scheduler reports to the block layer that there is an urgent
request pending, the device driver may decide to stop the transmission
of the current request in order to handle the urgent one. If the current
transmitted request is an urgent request - we don't want it to be
stopped.
Due to the above ROW scheduler won't notify of an urgent request if
there are urgent requests in flight.

Change-Id: I2fa186d911b908ec7611682b378b9cdc48637ac7
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:

	block/row-iosched.c

Signed-off-by: Seongmin Park <r_data@naver.com>
block: row: Update initial values of ROW data structures

This patch sets the initial values of internal ROW
parameters.

Change-Id: I38132062a7fcbe2e58b9cc757e55caac64d013dc
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
[smuckle@codeaurora.org: ported from msm-3.7]
Signed-off-by: Steve Muckle <smuckle@codeaurora.org>

Signed-off-by: Seongmin Park <r_data@naver.com>
block: Add support for reinsert a dispatched req

Add support for reinserting a dispatched request back to the
scheduler's internal data structures.
This capability is used by the device driver when it chooses to
interrupt the current request transmission and execute another (more
urgent) pending request. For example: interrupting long write in order
to handle pending read. The device driver re-inserts the
remaining write request back to the scheduler, to be rescheduled
for transmission later on.

Add API for verifying whether the current scheduler
supports reinserting requests mechanism. If reinsert mechanism isn't
supported by the scheduler, this code path will never be activated.

Change-Id: I5c982a66b651ebf544aae60063ac8a340d79e67f
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>

Conflicts:

	include/linux/elevator.h

Signed-off-by: Seongmin Park <r_data@naver.com>
block: Add API for urgent request handling

This patch add support in block & elevator layers for handling
urgent requests. The decision if a request is urgent or not is taken
by the scheduler. Urgent request notification is passed to the underlying
block device driver (eMMC for example). Block device driver may decide to
interrupt the currently running low priority request to serve the new
urgent request. By doing so READ latency is greatly reduced in read&write
collision scenarios.

Note that if the current scheduler doesn't implement the urgent request
mechanism, this code path is never activated.

Change-Id: I8aa74b9b45c0d3a2221bd4e82ea76eb4103e7cfa
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>
Signed-off-by: Seongmin Park <r_data@naver.com>
block: row-iosched.c: fix build error

Signed-off-by: Seongmin Park <r_data@naver.com>