02 Mar, 2013

1 commit

  • Pull new ARC architecture from Vineet Gupta:
    "Initial ARC Linux port with some fixes on top for 3.9-rc1:

    I would like to introduce the Linux port to ARC Processors (from
    Synopsys) for 3.9-rc1. The patch-set has been discussed on the public
    lists since Nov and has received a fair bit of review, specially from
    Arnd, tglx, Al and other subsystem maintainers for DeviceTree, kgdb...

    The arch bits are in arch/arc, some asm-generic changes (acked by
    Arnd), a minor change to PARISC (acked by Helge).

    The series is a touch bigger for a new port for 2 main reasons:

    1. It enables a basic kernel in first sub-series and adds
    ptrace/kgdb/.. later

    2. Some of the fallout of review (DeviceTree support, multi-platform-
    image support) were added on top of orig series, primarily to
    record the revision history.

    This updated pull request additionally contains

    - fixes due to our GNU tools catching up with the new syscall/ptrace
    ABI

    - some (minor) cross-arch Kconfig updates."

    * tag 'arc-v3.9-rc1-late' of git://git.kernel.org/pub/scm/linux/kernel/git/vgupta/arc: (82 commits)
    ARC: split elf.h into uapi and export it for userspace
    ARC: Fixup the current ABI version
    ARC: gdbserver using regset interface possibly broken
    ARC: Kconfig cleanup tracking cross-arch Kconfig pruning in merge window
    ARC: make a copy of flat DT
    ARC: [plat-arcfpga] DT arc-uart bindings change: "baud" => "current-speed"
    ARC: Ensure CONFIG_VIRT_TO_BUS is not enabled
    ARC: Fix pt_orig_r8 access
    ARC: [3.9] Fallout of hlist iterator update
    ARC: 64bit RTSC timestamp hardware issue
    ARC: Don't fiddle with non-existent caches
    ARC: Add self to MAINTAINERS
    ARC: Provide a default serial.h for uart drivers needing BASE_BAUD
    ARC: [plat-arcfpga] defconfig for fully loaded ARC Linux
    ARC: [Review] Multi-platform image #8: platform registers SMP callbacks
    ARC: [Review] Multi-platform image #7: SMP common code to use callbacks
    ARC: [Review] Multi-platform image #6: cpu-to-dma-addr optional
    ARC: [Review] Multi-platform image #5: NR_IRQS defined by ARC core
    ARC: [Review] Multi-platform image #4: Isolate platform headers
    ARC: [Review] Multi-platform image #3: switch to board callback
    ...

    Linus Torvalds
     

26 Feb, 2013

2 commits

  • Pull user namespace and namespace infrastructure changes from Eric W Biederman:
    "This set of changes starts with a few small enhnacements to the user
    namespace. reboot support, allowing more arbitrary mappings, and
    support for mounting devpts, ramfs, tmpfs, and mqueuefs as just the
    user namespace root.

    I do my best to document that if you care about limiting your
    unprivileged users that when you have the user namespace support
    enabled you will need to enable memory control groups.

    There is a minor bug fix to prevent overflowing the stack if someone
    creates way too many user namespaces.

    The bulk of the changes are a continuation of the kuid/kgid push down
    work through the filesystems. These changes make using uids and gids
    typesafe which ensures that these filesystems are safe to use when
    multiple user namespaces are in use. The filesystems converted for
    3.9 are ceph, 9p, afs, ocfs2, gfs2, ncpfs, nfs, nfsd, and cifs. The
    changes for these filesystems were a little more involved so I split
    the changes into smaller hopefully obviously correct changes.

    XFS is the only filesystem that remains. I was hoping I could get
    that in this release so that user namespace support would be enabled
    with an allyesconfig or an allmodconfig but it looks like the xfs
    changes need another couple of days before it they are ready."

    * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace: (93 commits)
    cifs: Enable building with user namespaces enabled.
    cifs: Convert struct cifs_ses to use a kuid_t and a kgid_t
    cifs: Convert struct cifs_sb_info to use kuids and kgids
    cifs: Modify struct smb_vol to use kuids and kgids
    cifs: Convert struct cifsFileInfo to use a kuid
    cifs: Convert struct cifs_fattr to use kuid and kgids
    cifs: Convert struct tcon_link to use a kuid.
    cifs: Modify struct cifs_unix_set_info_args to hold a kuid_t and a kgid_t
    cifs: Convert from a kuid before printing current_fsuid
    cifs: Use kuids and kgids SID to uid/gid mapping
    cifs: Pass GLOBAL_ROOT_UID and GLOBAL_ROOT_GID to keyring_alloc
    cifs: Use BUILD_BUG_ON to validate uids and gids are the same size
    cifs: Override unmappable incoming uids and gids
    nfsd: Enable building with user namespaces enabled.
    nfsd: Properly compare and initialize kuids and kgids
    nfsd: Store ex_anon_uid and ex_anon_gid as kuids and kgids
    nfsd: Modify nfsd4_cb_sec to use kuids and kgids
    nfsd: Handle kuids and kgids in the nfs4acl to posix_acl conversion
    nfsd: Convert nfsxdr to use kuids and kgids
    nfsd: Convert nfs3xdr to use kuids and kgids
    ...

    Linus Torvalds
     
  • Pull module update from Rusty Russell:
    "The sweeping change is to make add_taint() explicitly indicate whether
    to disable lockdep, but it's a mechanical change."

    * tag 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux:
    MODSIGN: Add option to not sign modules during modules_install
    MODSIGN: Add -s option to sign-file
    MODSIGN: Specify the hash algorithm on sign-file command line
    MODSIGN: Simplify Makefile with a Kconfig helper
    module: clean up load_module a little more.
    modpost: Ignore ARC specific non-alloc sections
    module: constify within_module_*
    taint: add explicit flag to show whether lock dep is still OK.
    module: printk message when module signature fail taints kernel.

    Linus Torvalds
     

22 Feb, 2013

2 commits

  • Pull misc ia64 bits from Tony Luck.

    * tag 'please-pull-misc-3.9' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux:
    MAINTAINERS: update SGI & ia64 Altix stuff
    sysctl: Enable IA64 "ignore-unaligned-usertrap" to be used cross-arch

    Linus Torvalds
     
  • Pull driver core patches from Greg Kroah-Hartman:
    "Here is the big driver core merge for 3.9-rc1

    There are two major series here, both of which touch lots of drivers
    all over the kernel, and will cause you some merge conflicts:

    - add a new function called devm_ioremap_resource() to properly be
    able to check return values.

    - remove CONFIG_EXPERIMENTAL

    Other than those patches, there's not much here, some minor fixes and
    updates"

    Fix up trivial conflicts

    * tag 'driver-core-3.9-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (221 commits)
    base: memory: fix soft/hard_offline_page permissions
    drivercore: Fix ordering between deferred_probe and exiting initcalls
    backlight: fix class_find_device() arguments
    TTY: mark tty_get_device call with the proper const values
    driver-core: constify data for class_find_device()
    firmware: Ignore abort check when no user-helper is used
    firmware: Reduce ifdef CONFIG_FW_LOADER_USER_HELPER
    firmware: Make user-mode helper optional
    firmware: Refactoring for splitting user-mode helper code
    Driver core: treat unregistered bus_types as having no devices
    watchdog: Convert to devm_ioremap_resource()
    thermal: Convert to devm_ioremap_resource()
    spi: Convert to devm_ioremap_resource()
    power: Convert to devm_ioremap_resource()
    mtd: Convert to devm_ioremap_resource()
    mmc: Convert to devm_ioremap_resource()
    mfd: Convert to devm_ioremap_resource()
    media: Convert to devm_ioremap_resource()
    iommu: Convert to devm_ioremap_resource()
    drm: Convert to devm_ioremap_resource()
    ...

    Linus Torvalds
     

20 Feb, 2013

3 commits

  • Pull async changes from Tejun Heo:
    "These are followups for the earlier deadlock issue involving async
    ending up waiting for itself through block requesting module[1]. The
    following changes are made by these commits.

    - Instead of requesting default elevator on each request_queue init,
    block now requests it once early during boot.

    - Kmod triggers warning if invoked from an async worker.

    - Async synchronization implementation has been reimplemented. It's
    a lot simpler now."

    * 'for-3.9-async' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq:
    async: initialise list heads to fix crash
    async: replace list of active domains with global list of pending items
    async: keep pending tasks on async_domain and remove async_pending
    async: use ULLONG_MAX for infinity cookie value
    async: bring sanity to the use of words domain and running
    async, kmod: warn on synchronous request_module() from async workers
    block: don't request module during elevator init
    init, block: try to load default elevator module early during boot

    Linus Torvalds
     
  • Pull scheduler changes from Ingo Molnar:
    "Main changes:

    - scheduler side full-dynticks (user-space execution is undisturbed
    and receives no timer IRQs) preparation changes that convert the
    cputime accounting code to be full-dynticks ready, from Frederic
    Weisbecker.

    - Initial sched.h split-up changes, by Clark Williams

    - select_idle_sibling() performance improvement by Mike Galbraith:

    " 1 tbench pair (worst case) in a 10 core + SMT package:

    pre 15.22 MB/sec 1 procs
    post 252.01 MB/sec 1 procs "

    - sched_rr_get_interval() ABI fix/change. We think this detail is not
    used by apps (so it's not an ABI in practice), but lets keep it
    under observation.

    - misc RT scheduling cleanups, optimizations"

    * 'sched-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
    sched/rt: Add header to
    cputime: Remove irqsave from seqlock readers
    sched, powerpc: Fix sched.h split-up build failure
    cputime: Restore CPU_ACCOUNTING config defaults for PPC64
    sched/rt: Move rt specific bits into new header file
    sched/rt: Add a tuning knob to allow changing SCHED_RR timeslice
    sched: Move sched.h sysctl bits into separate header
    sched: Fix signedness bug in yield_to()
    sched: Fix select_idle_sibling() bouncing cow syndrome
    sched/rt: Further simplify pick_rt_task()
    sched/rt: Do not account zero delta_exec in update_curr_rt()
    cputime: Safely read cputime of full dynticks CPUs
    kvm: Prepare to add generic guest entry/exit callbacks
    cputime: Use accessors to read task cputime stats
    cputime: Allow dynamic switch between tick/virtual based cputime accounting
    cputime: Generic on-demand virtual cputime accounting
    cputime: Move default nsecs_to_cputime() to jiffies based cputime file
    cputime: Librarize per nsecs resolution cputime definitions
    cputime: Avoid multiplication overflow on utime scaling
    context_tracking: Export context state for generic vtime
    ...

    Fix up conflict in kernel/context_tracking.c due to comment additions.

    Linus Torvalds
     
  • Pull irq core changes from Ingo Molnar:
    "The biggest changes are the IRQ-work and printk changes from Frederic
    Weisbecker, which prepare the code for 'full dynticks' (the ability to
    stop or slow down the periodic tick arbitrarily, not just in idle time
    as today):

    - Don't stop tick with irq works pending. This fix is generally
    useful and concerns archs that can't raise self IPIs.

    - Flush irq works before CPU offlining.

    - Introduce "lazy" irq works that can wait for the next tick to be
    executed, unless it's stopped.

    - Implement klogd wake up using irq work. This removes the ad-hoc
    printk_tick()/printk_needs_cpu() hooks and make it working even in
    dynticks mode.

    - Cleanups and fixes."

    * 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
    genirq: Export enable/disable_percpu_irq()
    arch Kconfig: Remove references to IRQ_PER_CPU
    irq_work: Remove return value from the irq_work_queue() function
    genirq: Avoid deadlock in spurious handling
    printk: Wake up klogd using irq_work
    irq_work: Make self-IPIs optable
    irq_work: Warn if there's still work on cpu_down
    irq_work: Flush work on CPU_DYING
    irq_work: Don't stop the tick with pending works
    nohz: Add API to check tick state
    irq_work: Remove CONFIG_HAVE_IRQ_WORK
    irq_work: Fix racy check on work pending flag
    irq_work: Fix racy IRQ_WORK_BUSY flag setting

    Linus Torvalds
     

16 Feb, 2013

1 commit

  • PARISC defines /proc/sys/kernel/unaligned-trap to runtime toggle
    unaligned access emulation.

    The exact mechanics of enablig/disabling are still arch specific, we can
    make the sysctl usable by other arches.

    Signed-off-by: Vineet Gupta
    Acked-by: Helge Deller
    Cc: "James E.J. Bottomley"
    Cc: Helge Deller
    Cc: "Eric W. Biederman"
    Cc: Serge Hallyn

    Vineet Gupta
     

13 Feb, 2013

8 commits


12 Feb, 2013

2 commits


08 Feb, 2013

3 commits

  • Commit abf917cd91cb ("cputime: Generic on-demand virtual cputime
    accounting") inadvertantly changed the default CPU_ACCOUNTING
    config for PPC64. Repair that.

    Signed-off-by: Stephen Rothwell
    Acked-by: Frederic Weisbecker
    Cc: Li Zhong
    Cc: Namhyung Kim
    Cc: Paul E. McKenney
    Cc: Paul Gortmaker
    Cc: Peter Zijlstra
    Cc: Steven Rostedt
    Cc: ppc-dev
    Cc: Benjamin Herrenschmidt
    Link: http://lkml.kernel.org/r/20130208141938.f31b7b9e1acac5bbe769ee4c@canb.auug.org.au
    Signed-off-by: Ingo Molnar

    Stephen Rothwell
     
  • Move rt scheduler definitions out of include/linux/sched.h into
    new file include/linux/sched/rt.h

    Signed-off-by: Clark Williams
    Cc: Peter Zijlstra
    Cc: Steven Rostedt
    Link: http://lkml.kernel.org/r/20130207094707.7b9f825f@riff.lan
    Signed-off-by: Ingo Molnar

    Clark Williams
     
  • Move the sysctl-related bits from include/linux/sched.h into
    a new file: include/linux/sched/sysctl.h. Then update source
    files requiring access to those bits by including the new
    header file.

    Signed-off-by: Clark Williams
    Cc: Peter Zijlstra
    Cc: Steven Rostedt
    Link: http://lkml.kernel.org/r/20130207094659.06dced96@riff.lan
    Signed-off-by: Ingo Molnar

    Clark Williams
     

07 Feb, 2013

1 commit

  • All in-kernel users of class_find_device() don't really need mutable
    data for match callback.

    In two places (kernel/power/suspend_test.c, drivers/scsi/osd/osd_uld.c)
    this patch changes match callbacks to use const search data.

    The const is propagated to rtc_class_open() and power_supply_get_by_name()
    parameters.

    Note that there's a dev reference leak in suspend_test.c that's not
    touched in this patch.

    Signed-off-by: Michał Mirosław
    Acked-by: Grant Likely
    Signed-off-by: Greg Kroah-Hartman

    Michał Mirosław
     

05 Feb, 2013

3 commits

  • …x/kernel/git/frederic/linux-dynticks into sched/core

    Pull full-dynticks (user-space execution is undisturbed and
    receives no timer IRQs) preparation changes that convert the
    cputime accounting code to be full-dynticks ready,
    from Frederic Weisbecker:

    "This implements the cputime accounting on full dynticks CPUs.

    Typical cputime stats infrastructure relies on the timer tick and
    its periodic polling on the CPU to account the amount of time
    spent by the CPUs and the tasks per high level domains such as
    userspace, kernelspace, guest, ...

    Now we are preparing to implement full dynticks capability on
    Linux for Real Time and HPC users who want full CPU isolation.
    This feature requires a cputime accounting that doesn't depend
    on the timer tick.

    To implement it, this new cputime infrastructure plugs into
    kernel/user/guest boundaries to take snapshots of cputime and
    flush these to the stats when needed. This performs pretty
    much like CONFIG_VIRT_CPU_ACCOUNTING except that context location
    and cputime snaphots are synchronized between write and read
    side such that the latter can safely retrieve the pending tickless
    cputime of a task and add it to its latest cputime snapshot to
    return the correct result to the user."

    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Signed-off-by: Ingo Molnar <mingo@kernel.org>

    Ingo Molnar
     
  • Conflicts:
    kernel/irq_work.c

    Add support for printk in full dynticks CPU.

    * Don't stop tick with irq works pending. This
    fix is generally useful and concerns archs that
    can't raise self IPIs.

    * Flush irq works before CPU offlining.

    * Introduce "lazy" irq works that can wait for the
    next tick to be executed, unless it's stopped.

    * Implement klogd wake up using irq work. This
    removes the ad-hoc printk_tick()/printk_needs_cpu()
    hooks and make it working even in dynticks mode.

    Signed-off-by: Frederic Weisbecker

    Frederic Weisbecker
     
  • …/linux-rcu into core/rcu

    Pull RCU updates from Paul E. McKenney:

    1. Changes to rcutorture and to RCU documentation. Posted to LKML at
    https://lkml.org/lkml/2013/1/26/188.

    2. Enhancements to uniprocessor handling in tiny RCU. Posted to LKML
    at https://lkml.org/lkml/2013/1/27/2.

    3. Tag RCU callbacks with grace-period number to simplify callback
    advancement. Posted to LKML at https://lkml.org/lkml/2013/1/26/203.

    4. Miscellaneous fixes. Posted to LKML at https://lkml.org/lkml/2013/1/26/204.

    Signed-off-by: Ingo Molnar <mingo@kernel.org>

    Ingo Molnar
     

31 Jan, 2013

2 commits

  • Pull x86 fixes from Peter Anvin:
    "This is a collection of miscellaneous fixes, the most important one is
    the fix for the Samsung laptop bricking issue (auto-blacklisting the
    samsung-laptop driver); the efi_enabled() changes you see below are
    prerequisites for that fix.

    The other issues fixed are booting on OLPC XO-1.5, an UV fix, NMI
    debugging, and requiring CAP_SYS_RAWIO for MSR references, just as
    with I/O port references."

    * 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
    samsung-laptop: Disable on EFI hardware
    efi: Make 'efi_enabled' a function to query EFI facilities
    smp: Fix SMP function call empty cpu mask race
    x86/msr: Add capabilities check
    x86/dma-debug: Bump PREALLOC_DMA_DEBUG_ENTRIES
    x86/olpc: Fix olpc-xo1-sci.c build errors
    arch/x86/platform/uv: Fix incorrect tlb flush all issue
    x86-64: Fix unwind annotations in recent NMI changes
    x86-32: Start out cr0 clean, disable paging before modifying cr3/4

    Linus Torvalds
     
  • Originally 'efi_enabled' indicated whether a kernel was booted from
    EFI firmware. Over time its semantics have changed, and it now
    indicates whether or not we are booted on an EFI machine with
    bit-native firmware, e.g. 64-bit kernel with 64-bit firmware.

    The immediate motivation for this patch is the bug report at,

    https://bugs.launchpad.net/ubuntu-cdimage/+bug/1040557

    which details how running a platform driver on an EFI machine that is
    designed to run under BIOS can cause the machine to become
    bricked. Also, the following report,

    https://bugzilla.kernel.org/show_bug.cgi?id=47121

    details how running said driver can also cause Machine Check
    Exceptions. Drivers need a new means of detecting whether they're
    running on an EFI machine, as sadly the expression,

    if (!efi_enabled)

    hasn't been a sufficient condition for quite some time.

    Users actually want to query 'efi_enabled' for different reasons -
    what they really want access to is the list of available EFI
    facilities.

    For instance, the x86 reboot code needs to know whether it can invoke
    the ResetSystem() function provided by the EFI runtime services, while
    the ACPI OSL code wants to know whether the EFI config tables were
    mapped successfully. There are also checks in some of the platform
    driver code to simply see if they're running on an EFI machine (which
    would make it a bad idea to do BIOS-y things).

    This patch is a prereq for the samsung-laptop fix patch.

    Cc: David Airlie
    Cc: Corentin Chary
    Cc: Matthew Garrett
    Cc: Dave Jiang
    Cc: Olof Johansson
    Cc: Peter Jones
    Cc: Colin Ian King
    Cc: Steve Langasek
    Cc: Tony Luck
    Cc: Konrad Rzeszutek Wilk
    Cc: Rafael J. Wysocki
    Cc:
    Signed-off-by: Matt Fleming
    Signed-off-by: H. Peter Anvin

    Matt Fleming
     

29 Jan, 2013

2 commits

  • The TINY_PREEMPT_RCU is complex, does not provide that much memory
    savings, and therefore TREE_PREEMPT_RCU should be used instead. The
    systems where the difference between TINY_PREEMPT_RCU and TREE_PREEMPT_RCU
    are quite small compared to the memory footprint of CONFIG_PREEMPT.

    This commit therefore takes a first step towards eliminating
    TINY_PREEMPT_RCU by allowing TREE_PREEMPT_RCU to be configured on !SMP
    systems.

    Signed-off-by: Paul E. McKenney
    Reviewed-by: Josh Triplett

    Paul E. McKenney
     
  • Tiny RCU has historically omitted RCU CPU stall warnings in order to
    reduce memory requirements, however, lack of these warnings caused
    Thomas Gleixner some debugging pain recently. Therefore, this commit
    adds RCU CPU stall warnings to tiny RCU if RCU_TRACE=y. This keeps
    the memory footprint small, while still enabling CPU stall warnings
    in kernels built to enable them.

    Updated to include Josh Triplett's suggested use of RCU_STALL_COMMON
    config variable to simplify #if expressions.

    Reported-by: Thomas Gleixner
    Signed-off-by: Paul E. McKenney
    Signed-off-by: Paul E. McKenney
    Reviewed-by: Josh Triplett

    Paul E. McKenney
     

28 Jan, 2013

1 commit

  • If we want to stop the tick further idle, we need to be
    able to account the cputime without using the tick.

    Virtual based cputime accounting solves that problem by
    hooking into kernel/user boundaries.

    However implementing CONFIG_VIRT_CPU_ACCOUNTING require
    low level hooks and involves more overhead. But we already
    have a generic context tracking subsystem that is required
    for RCU needs by archs which plan to shut down the tick
    outside idle.

    This patch implements a generic virtual based cputime
    accounting that relies on these generic kernel/user hooks.

    There are some upsides of doing this:

    - This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING
    if context tracking is already built (already necessary for RCU in full
    tickless mode).

    - We can rely on the generic context tracking subsystem to dynamically
    (de)activate the hooks, so that we can switch anytime between virtual
    and tick based accounting. This way we don't have the overhead
    of the virtual accounting when the tick is running periodically.

    And one downside:

    - There is probably more overhead than a native virtual based cputime
    accounting. But this relies on hooks that are already set anyway.

    Signed-off-by: Frederic Weisbecker
    Cc: Andrew Morton
    Cc: Ingo Molnar
    Cc: Li Zhong
    Cc: Namhyung Kim
    Cc: Paul E. McKenney
    Cc: Paul Gortmaker
    Cc: Peter Zijlstra
    Cc: Steven Rostedt
    Cc: Thomas Gleixner

    Frederic Weisbecker
     

27 Jan, 2013

1 commit


26 Jan, 2013

1 commit


25 Jan, 2013

2 commits


24 Jan, 2013

2 commits


21 Jan, 2013

1 commit

  • Pull misc syscall fixes from Al Viro:

    - compat syscall fixes (discussed back in December)

    - a couple of "make life easier for sigaltstack stuff by reducing
    inter-tree dependencies"

    - fix up compiler/asmlinkage calling convention disagreement of
    sys_clone()

    - misc

    * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/signal:
    sys_clone() needs asmlinkage_protect
    make sure that /linuxrc has std{in,out,err}
    x32: fix sigtimedwait
    x32: fix waitid()
    switch compat_sys_wait4() and compat_sys_waitid() to COMPAT_SYSCALL_DEFINE
    switch compat_sys_sigaltstack() to COMPAT_SYSCALL_DEFINE
    CONFIG_GENERIC_SIGALTSTACK build breakage with asm-generic/syscalls.h
    Ensure that kernel_init_freeable() is not inlined into non __init code

    Linus Torvalds
     

20 Jan, 2013

1 commit


19 Jan, 2013

1 commit

  • This patch adds default module loading and uses it to load the default
    block elevator. During boot, it's called right after initramfs or
    initrd is made available and right before control is passed to
    userland. This ensures that as long as the modules are available in
    the usual places in initramfs, initrd or the root filesystem, the
    default modules are loaded as soon as possible.

    This will replace the on-demand elevator module loading from elevator
    init path.

    v2: Fixed build breakage when !CONFIG_BLOCK. Reported by kbuild test
    robot.

    Signed-off-by: Tejun Heo
    Cc: Jens Axboe
    Cc: Arjan van de Ven
    Cc: Linus Torvalds
    Cc: Alex Riesen
    Cc: Fengguang We

    Tejun Heo