binfmt_elf.c: use get_random_int() to fix entropy depleting

Changes:
--------
v4->v3:
- s/random_stack_user()/get_atrandom_bytes()/
- Move this function to ahead of its use to avoid the predeclaration.

v3->v2:
- Tweak code comments of random_stack_user().
- Remove redundant bits mask and shift upon the random variable.

v2->v1:
- Fix random copy to check up buffer length that are not 4-byte multiples.

v3 can be found at:
http://www.spinics.net/lists/linux-fsdevel/msg59597.html
v2 can be found at:
http://www.spinics.net/lists/linux-fsdevel/msg59418.html
v1 can be found at:
http://www.spinics.net/lists/linux-fsdevel/msg59128.html

Thanks,
-Jeff

Entropy is quickly depleted under normal operations like ls(1), cat(1),
etc...  between 2.6.30 to current mainline, for instance:

$ cat /proc/sys/kernel/random/entropy_avail
3428
$ cat /proc/sys/kernel/random/entropy_avail
2911
$cat /proc/sys/kernel/random/entropy_avail
2620

We observed this problem has been occurring since 2.6.30 with
fs/binfmt_elf.c: create_elf_tables()->get_random_bytes(), introduced by
f06295b44c296c8f ("ELF: implement AT_RANDOM for glibc PRNG seeding").

/*
 * Generate 16 random bytes for userspace PRNG seeding.
 */
get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes));

The patch introduces a wrapper around get_random_int() which has lower
overhead than calling get_random_bytes() directly.

With this patch applied:
$ cat /proc/sys/kernel/random/entropy_avail
2731
$ cat /proc/sys/kernel/random/entropy_avail
2802
$ cat /proc/sys/kernel/random/entropy_avail
2878

Analyzed by John Sobecki.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Dilger <aedilger@gmail.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnn@arndb.de>
Cc: John Sobecki <john.sobecki@oracle.com>
Cc: James Morris <james.l.morris@oracle.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Ted Ts'o <tytso@mit.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ulrich Drepper <drepper@redhat.com>
block: Adding ROW scheduling algorithm

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.
The requests are kept in queues according to their priority. The dispatch
is done in a Round Robin manner with a different slice for each queue.
READ request queues get bigger dispatch quantum than the write requests.

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

Conflicts:

	block/Kconfig.iosched
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>
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>
block:row: fix idling mechanism in ROW

This patch addresses the following issues found in the ROW idling
mechanism:
1. Fix the delay passed to queue_delayed_work (pass actual delay
   and not the time when to start the work)
2. Change the idle time and the idling-trigger frequency to be
   HZ dependent (instead of using msec_to_jiffies())
3. Destroy idle_workqueue() in queue_exit

Change-Id: If86513ad6b4be44fb7a860f29bd2127197d8d5bf
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>

Conflicts:
	block/row-iosched.c
row: Adding support for reinsert already dispatched req

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.

Change-Id: I70954df300774409c25b5821465fb3aa33d8feb5
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
row: Add support for urgent request handling

This patch adds support for handling urgent requests.
ROW queue can be marked as "urgent" so if it was un-served in last
dispatch cycle and a request was added to it - it will trigger
issuing an urgent-request-notification to the block device driver.
The block device driver may choose at stop the transmission of current
ongoing request to handle the urgent one. Foe example: long WRITE may
be stopped to handle an urgent READ. This decreases READ latency.

Change-Id: I84954c13f5e3b1b5caeadc9fe1f9aa21208cb35e
Signed-off-by: Tatyana Brokhman <tlinder@codeaurora.org>
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>
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>
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>
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>
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>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.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>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>