1. 07 Jan, 2011 40 commits
    • Ike Panhc's avatar
      ideapad: add platform driver for ideapad · 98ee6919
      Ike Panhc authored
      Create /sys/devices/platform/ideapad for nodes of ideapad landing.
      Signed-off-by: default avatarIke Panhc <ike.pan@canonical.com>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      98ee6919
    • Namhyung Kim's avatar
      fujitsu-laptop: fix compiler warning on pnp_ids · 9c232250
      Namhyung Kim authored
      Annotate pnp_ids as '__used' to fix following warning:
      
        CC      drivers/platform/x86/fujitsu-laptop.o
      drivers/platform/x86/fujitsu-laptop.c:1243: warning: ‘pnp_ids’ defined but not used
      Signed-off-by: default avatarNamhyung Kim <namhyung@gmail.com>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      9c232250
    • Dan Carpenter's avatar
      WMI: return error if wmi_create_device() fails · e1e0dacb
      Dan Carpenter authored
      The break resets the retval to 0 but we want to return an error code.
      This was introduced in c64eefd4 "WMI: embed struct device directly
      into wmi_block"
      Signed-off-by: default avatarDan Carpenter <error27@gmail.com>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      Acked-by: default avatarDmitry Torokhov <dtor@mail.ru>
      e1e0dacb
    • Corentin Chary's avatar
      eeepc-wmi: never load if legacy device is enabled · d358cb55
      Corentin Chary authored
      If legacy device (SB.ATKD - ASUS010) used by eeepc-laptop
      is enabled, don't allow eeepc-wmi to load because:
      - eeepc-laptop may be loaded, and can conflict with
        eeepc-wmi (they both try to register eeepc::touchpad
        led for example).
      - the WMI interface is inteded to be used when the OS is
        not detected as Win 7. And when this is the case, the
        ASUS010 device is disabled.
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      d358cb55
    • Corentin Chary's avatar
      eeepc-laptop: add a getter for touchpad led · 62a75d83
      Corentin Chary authored
      Allow te get the current led state in a more accurate way.
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      62a75d83
    • Corentin Chary's avatar
      eeepc-wmi: remove unneeded static · dfed65d5
      Corentin Chary authored
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      dfed65d5
    • Corentin Chary's avatar
      eeepc-wmi: claim eeepc-wmi maintainership · 4c4edfa3
      Corentin Chary authored
      Since eeepc-wmi has currently no official maintainer, I claim
      maintainership of this driver, and add it to the acpi4asus project.
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      4c4edfa3
    • Corentin Chary's avatar
    • Corentin Chary's avatar
      eeepc-wmi: add debugfs entries · 8c1b2d83
      Corentin Chary authored
      eeepc-wmi/    - debugfs root directory
        dev_id      - current dev_id
        ctrl_param  - current ctrl_param
        devs        - call DEVS(dev_id, ctrl_param) and print result
        dsts        - call DSTS(dev_id)  and print result
      
      DEVS and DSTS are the main functions used in eeepc-wmi, this
      will allow to test new features without patching the drivers.
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      8c1b2d83
    • Corentin Chary's avatar
    • Corentin Chary's avatar
      eeepc-wmi: add rfkill support for wlan, bluetooth and 3g · ba48fdb9
      Corentin Chary authored
      wimax support is missing because I don't have any DSDT
      with WMI and wimax support.
      
      Most of the code comes from eeepc-laptop.
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      ba48fdb9
    • Corentin Chary's avatar
      eeepc-wmi: add touchpad led support · 084fca63
      Corentin Chary authored
      Most of the code comes from eeepc-laptop.
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      084fca63
    • Corentin Chary's avatar
      eeepc-wmi: rework eeepc_wmi_init and eeepc_wmi_exit · 27c136c8
      Corentin Chary authored
      The old code was using platform_driver.probe to initialize
      eeepc_wmi context. That's a mistake because if probe fail,
      eeepc_platform_register() won't tell anyone, and chaos will happen.
      
      Wrap add and remove code inside eeepc_wmi_add() / eeepc_wmi_remove(),
      and try to use the static platform_device only in eeepc_wmi_init()
      and eeepc_wmi_exit()
      
      The code is now very similar to eeepc-laptop, except eeepc_laptop_add
      and eeepc_laptop_remove are called from acpi_driver, not module
      init/exit functions, but WMI doesn't provide such functionalities (yet ?).
      Signed-off-by: default avatarCorentin Chary <corentincj@iksaif.net>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      27c136c8
    • Herton Ronaldo Krzesinski's avatar
      classmate-laptop: add missing input_sync call · 72135d21
      Herton Ronaldo Krzesinski authored
      Add missing input_sync call in cmpc_keys_handler function.
      Signed-off-by: default avatarHerton Ronaldo Krzesinski <herton@mandriva.com.br>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      Acked-by: default avatarThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
      72135d21
    • Herton Ronaldo Krzesinski's avatar
      classmate-laptop: little optimization for cmpc_rfkill_block · 698e1641
      Herton Ronaldo Krzesinski authored
      We don't need to call bios/acpi (cmpc_set_rfkill_wlan) if the blocked
      state is already set to the same value (little optimization). This can
      happen for example if we initialize the module with same initial
      hardware state (rfkill core always call cmpc_rfkill_block on
      initialization here).
      
      Also GWRI method only accepts 0 or 1 for setting rfkill block, as can be
      seen on AML code from acpidump->DSDT from a classmate sample I have, so
      should be fine setting state only to 0 or 1 directly.
      Signed-off-by: default avatarHerton Ronaldo Krzesinski <herton@mandriva.com.br>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      Acked-by: default avatarThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
      698e1641
    • Colin King's avatar
      WMI: Cater for multiple events with same GUID · 58f6425e
      Colin King authored
      WMI data blocks can contain WMI events with the same GUID but with
      different notifiy_ids, for example volume up/down hotkeys.
      This patch enables a single event handler to be registered and
      unregistered against all events with same GUID but different
      notify_ids.  Since an event handler is passed the notify_id of
      an event it can can differentiate between the different events.
      
      The patch also ensures we only register and unregister a device per
      unique GUID.
      Signed-off-by: default avatarColin Ian King <colin.king@canonical.com>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      58f6425e
    • Joe Perches's avatar
      3098064d
    • Sreedhara DS's avatar
      intel_scu_ipc: Utility driver for intel scu ipc · 5369c02d
      Sreedhara DS authored
      This driver implements ioctl and interfaces with intel scu ipc driver. It
      is used to access pmic/msic registers from user space and firmware update
      utility.
      Signed-off-by: default avatarSreedhara DS <sreedhara.ds@intel.com>
      [Extensive clean up and debug]
      Signed-off-by: default avatarAlan Cox <alan@linux.intel.com>
      Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
      5369c02d
    • Linus Torvalds's avatar
      Merge branch 'usb-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6 · 3e5b08cb
      Linus Torvalds authored
      * 'usb-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb-2.6: (144 commits)
        USB: add support for Dream Cheeky DL100B Webmail Notifier (1d34:0004)
        USB: serial: ftdi_sio: add support for TIOCSERGETLSR
        USB: ehci-mxc: Setup portsc register prior to accessing OTG viewport
        USB: atmel_usba_udc: fix freeing irq in usba_udc_remove()
        usb: ehci-omap: fix tll channel enable mask
        usb: ohci-omap3: fix trivial typo
        USB: gadget: ci13xxx: don't assume that PAGE_SIZE is 4096
        USB: gadget: ci13xxx: fix complete() callback for no_interrupt rq's
        USB: gadget: update ci13xxx to work with g_ether
        USB: gadgets: ci13xxx: fix probing of compiled-in gadget drivers
        Revert "USB: musb: pm: don't rely fully on clock support"
        Revert "USB: musb: blackfin: pm: make it work"
        USB: uas: Use GFP_NOIO instead of GFP_KERNEL in I/O submission path
        USB: uas: Ensure we only bind to a UAS interface
        USB: uas: Rename sense pipe and sense urb to status pipe and status urb
        USB: uas: Use kzalloc instead of kmalloc
        USB: uas: Fix up the Sense IU
        usb: musb: core: kill unneeded #include's
        DA8xx: assign name to MUSB IRQ resource
        usb: gadget: g_ncm added
        ...
      
      Manually fix up trivial conflicts in USB Kconfig changes in:
      	arch/arm/mach-omap2/Kconfig
      	arch/sh/Kconfig
      	drivers/usb/Kconfig
      	drivers/usb/host/ehci-hcd.c
      and annoying chip clock data conflicts in:
      	arch/arm/mach-omap2/clock3xxx_data.c
      	arch/arm/mach-omap2/clock44xx_data.c
      3e5b08cb
    • Linus Torvalds's avatar
      Merge git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6 · da40d036
      Linus Torvalds authored
      * git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi-misc-2.6: (147 commits)
        [SCSI] arcmsr: fix write to device check
        [SCSI] lpfc: lower stack use in lpfc_fc_frame_check
        [SCSI] eliminate an unnecessary local variable from scsi_remove_target()
        [SCSI] libiscsi: use bh locking instead of irq with session lock
        [SCSI] libiscsi: do not take host lock in queuecommand
        [SCSI] be2iscsi: fix null ptr when accessing task hdr
        [SCSI] be2iscsi: fix gfp use in alloc_pdu
        [SCSI] libiscsi: add more informative failure message during iscsi scsi eh
        [SCSI] gdth: Add missing call to gdth_ioctl_free
        [SCSI] bfa: remove unused defintions and misc cleanups
        [SCSI] bfa: remove inactive functions
        [SCSI] bfa: replace bfa_assert with WARN_ON
        [SCSI] qla2xxx: Use sg_next to fetch next sg element while walking sg list.
        [SCSI] qla2xxx: Fix to avoid recursive lock failure during BSG timeout.
        [SCSI] qla2xxx: Remove code to not reset ISP82xx on failure.
        [SCSI] qla2xxx: Display mailbox register 4 during 8012 AEN for ISP82XX parts.
        [SCSI] qla2xxx: Don't perform a BIG_HAMMER if Get-ID (0x20) mailbox command fails on CNAs.
        [SCSI] qla2xxx: Remove redundant module parameter permission bits
        [SCSI] qla2xxx: Add sysfs node for displaying board temperature.
        [SCSI] qla2xxx: Code cleanup to remove unwanted comments and code.
        ...
      da40d036
    • Dan Carpenter's avatar
      input/tc3589x: fix compile error · aa58abc2
      Dan Carpenter authored
      There was a semi-colon missing and it broke the compile.
      Signed-off-by: default avatarDan Carpenter <error27@gmail.com>
      Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
      Signed-off-by: default avatarLinus Walleij <linus.walleij@stericsson.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      aa58abc2
    • Linus Torvalds's avatar
      Merge branch 'vfs-scale-working' of... · b4a45f5f
      Linus Torvalds authored
      Merge branch 'vfs-scale-working' of git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin
      
      * 'vfs-scale-working' of git://git.kernel.org/pub/scm/linux/kernel/git/npiggin/linux-npiggin: (57 commits)
        fs: scale mntget/mntput
        fs: rename vfsmount counter helpers
        fs: implement faster dentry memcmp
        fs: prefetch inode data in dcache lookup
        fs: improve scalability of pseudo filesystems
        fs: dcache per-inode inode alias locking
        fs: dcache per-bucket dcache hash locking
        bit_spinlock: add required includes
        kernel: add bl_list
        xfs: provide simple rcu-walk ACL implementation
        btrfs: provide simple rcu-walk ACL implementation
        ext2,3,4: provide simple rcu-walk ACL implementation
        fs: provide simple rcu-walk generic_check_acl implementation
        fs: provide rcu-walk aware permission i_ops
        fs: rcu-walk aware d_revalidate method
        fs: cache optimise dentry and inode for rcu-walk
        fs: dcache reduce branches in lookup path
        fs: dcache remove d_mounted
        fs: fs_struct use seqlock
        fs: rcu-walk for path lookup
        ...
      b4a45f5f
    • Nick Piggin's avatar
      fs: scale mntget/mntput · b3e19d92
      Nick Piggin authored
      The problem that this patch aims to fix is vfsmount refcounting scalability.
      We need to take a reference on the vfsmount for every successful path lookup,
      which often go to the same mount point.
      
      The fundamental difficulty is that a "simple" reference count can never be made
      scalable, because any time a reference is dropped, we must check whether that
      was the last reference. To do that requires communication with all other CPUs
      that may have taken a reference count.
      
      We can make refcounts more scalable in a couple of ways, involving keeping
      distributed counters, and checking for the global-zero condition less
      frequently.
      
      - check the global sum once every interval (this will delay zero detection
        for some interval, so it's probably a showstopper for vfsmounts).
      
      - keep a local count and only taking the global sum when local reaches 0 (this
        is difficult for vfsmounts, because we can't hold preempt off for the life of
        a reference, so a counter would need to be per-thread or tied strongly to a
        particular CPU which requires more locking).
      
      - keep a local difference of increments and decrements, which allows us to sum
        the total difference and hence find the refcount when summing all CPUs. Then,
        keep a single integer "long" refcount for slow and long lasting references,
        and only take the global sum of local counters when the long refcount is 0.
      
      This last scheme is what I implemented here. Attached mounts and process root
      and working directory references are "long" references, and everything else is
      a short reference.
      
      This allows scalable vfsmount references during path walking over mounted
      subtrees and unattached (lazy umounted) mounts with processes still running
      in them.
      
      This results in one fewer atomic op in the fastpath: mntget is now just a
      per-CPU inc, rather than an atomic inc; and mntput just requires a spinlock
      and non-atomic decrement in the common case. However code is otherwise bigger
      and heavier, so single threaded performance is basically a wash.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      b3e19d92
    • Nick Piggin's avatar
      fs: rename vfsmount counter helpers · c6653a83
      Nick Piggin authored
      Suggested by Andreas, mnt_ prefix is clearer namespace, follows kernel
      conventions better, and is easier for tab complete. I introduced these
      names so I'll admit they were not good choices.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      c6653a83
    • Nick Piggin's avatar
      fs: implement faster dentry memcmp · 9d55c369
      Nick Piggin authored
      The standard memcmp function on a Westmere system shows up hot in
      profiles in the `git diff` workload (both parallel and single threaded),
      and it is likely due to the costs associated with trapping into
      microcode, and little opportunity to improve memory access (dentry
      name is not likely to take up more than a cacheline).
      
      So replace it with an open-coded byte comparison. This increases code
      size by 8 bytes in the critical __d_lookup_rcu function, but the
      speedup is huge, averaging 10 runs of each:
      
      git diff st   user   sys   elapsed  CPU
      before        1.15   2.57  3.82      97.1
      after         1.14   2.35  3.61      96.8
      
      git diff mt   user   sys   elapsed  CPU
      before        1.27   3.85  1.46     349
      after         1.26   3.54  1.43     333
      
      Elapsed time for single threaded git diff at 95.0% confidence:
              -0.21  +/- 0.01
              -5.45% +/- 0.24%
      
      It's -0.66% +/- 0.06% elapsed time on my Opteron, so rep cmp costs on the
      fam10h seem to be relatively smaller, but there is still a win.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      9d55c369
    • Nick Piggin's avatar
      fs: prefetch inode data in dcache lookup · e1bb5782
      Nick Piggin authored
      This makes single threaded git diff -1.25% +/- 0.05% elapsed time on my
      2s12c24t Westmere system, and -0.86% +/- 0.05% on my 2s8c Barcelona, by
      prefetching the important first cacheline of the inode in while we do the
      actual name compare and other operations on the dentry.
      
      There was no measurable slowdown in the single file stat case, or the creat
      case (where negative dentries would be common).
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      e1bb5782
    • Nick Piggin's avatar
      fs: improve scalability of pseudo filesystems · 4b936885
      Nick Piggin authored
      Regardless of how much we possibly try to scale dcache, there is likely
      always going to be some fundamental contention when adding or removing children
      under the same parent. Pseudo filesystems do not seem need to have connected
      dentries because by definition they are disconnected.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      4b936885
    • Nick Piggin's avatar
      fs: dcache per-inode inode alias locking · 873feea0
      Nick Piggin authored
      dcache_inode_lock can be replaced with per-inode locking. Use existing
      inode->i_lock for this. This is slightly non-trivial because we sometimes
      need to find the inode from the dentry, which requires d_inode to be
      stabilised (either with refcount or d_lock).
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      873feea0
    • Nick Piggin's avatar
      fs: dcache per-bucket dcache hash locking · ceb5bdc2
      Nick Piggin authored
      We can turn the dcache hash locking from a global dcache_hash_lock into
      per-bucket locking.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      ceb5bdc2
    • Nick Piggin's avatar
      bit_spinlock: add required includes · 626d6074
      Nick Piggin authored
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      626d6074
    • Nick Piggin's avatar
      kernel: add bl_list · 4e35e607
      Nick Piggin authored
      Introduce a type of hlist that can support the use of the lowest bit in the
      hlist_head. This will be subsequently used to implement per-bucket bit spinlock
      for inode and dentry hashes, and may be useful in other cases such as network
      hashes.
      Reviewed-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      4e35e607
    • Nick Piggin's avatar
      xfs: provide simple rcu-walk ACL implementation · 880566e1
      Nick Piggin authored
      This simple implementation just checks for no ACLs on the inode, and
      if so, then the rcu-walk may proceed, otherwise fail it.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      880566e1
    • Nick Piggin's avatar
      btrfs: provide simple rcu-walk ACL implementation · 258a5aa8
      Nick Piggin authored
      This simple implementation just checks for no ACLs on the inode, and
      if so, then the rcu-walk may proceed, otherwise fail it.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      258a5aa8
    • Nick Piggin's avatar
      ext2,3,4: provide simple rcu-walk ACL implementation · 73598611
      Nick Piggin authored
      This simple implementation just checks for no ACLs on the inode, and
      if so, then the rcu-walk may proceed, otherwise fail it.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      73598611
    • Nick Piggin's avatar
      fs: provide simple rcu-walk generic_check_acl implementation · 1e1743eb
      Nick Piggin authored
      This simple implementation just checks for no ACLs on the inode, and
      if so, then the rcu-walk may proceed, otherwise fail it.
      
      This could easily be extended to put acls under RCU and check them
      under seqlock, if need be. But this implementation is enough to show
      the rcu-walk aware permissions code for path lookups is working, and
      will handle cases where there are no ACLs or ACLs in just the final
      element.
      
      This patch implicity converts tmpfs to rcu-aware permission check.
      Subsequent patches onvert ext*, xfs, and, btrfs. Each of these uses
      acl/permission code in a different way, so convert them all to provide
      templates and proof of concept.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      1e1743eb
    • Nick Piggin's avatar
      fs: provide rcu-walk aware permission i_ops · b74c79e9
      Nick Piggin authored
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      b74c79e9
    • Nick Piggin's avatar
      fs: rcu-walk aware d_revalidate method · 34286d66
      Nick Piggin authored
      Require filesystems be aware of .d_revalidate being called in rcu-walk
      mode (nd->flags & LOOKUP_RCU). For now do a simple push down, returning
      -ECHILD from all implementations.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      34286d66
    • Nick Piggin's avatar
      fs: cache optimise dentry and inode for rcu-walk · 44a7d7a8
      Nick Piggin authored
      Put dentry and inode fields into top of data structure.  This allows RCU path
      traversal to perform an RCU dentry lookup in a path walk by touching only the
      first 56 bytes of the dentry.
      
      We also fit in 8 bytes of inline name in the first 64 bytes, so for short
      names, only 64 bytes needs to be touched to perform the lookup. We should
      get rid of the hash->prev pointer from the first 64 bytes, and fit 16 bytes
      of name in there, which will take care of 81% rather than 32% of the kernel
      tree.
      
      inode is also rearranged so that RCU lookup will only touch a single cacheline
      in the inode, plus one in the i_ops structure.
      
      This is important for directory component lookups in RCU path walking. In the
      kernel source, directory names average is around 6 chars, so this works.
      
      When we reach the last element of the lookup, we need to lock it and take its
      refcount which requires another cacheline access.
      
      Align dentry and inode operations structs, so members will be at predictable
      offsets and we can group common operations into head of structure.
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      44a7d7a8
    • Nick Piggin's avatar
      fs: dcache reduce branches in lookup path · fb045adb
      Nick Piggin authored
      Reduce some branches and memory accesses in dcache lookup by adding dentry
      flags to indicate common d_ops are set, rather than having to check them.
      This saves a pointer memory access (dentry->d_op) in common path lookup
      situations, and saves another pointer load and branch in cases where we
      have d_op but not the particular operation.
      
      Patched with:
      
      git grep -E '[.>]([[:space:]])*d_op([[:space:]])*=' | xargs sed -e 's/\([^\t ]*\)->d_op = \(.*\);/d_set_d_op(\1, \2);/' -e 's/\([^\t ]*\)\.d_op = \(.*\);/d_set_d_op(\&\1, \2);/' -i
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      fb045adb
    • Nick Piggin's avatar
      fs: dcache remove d_mounted · 5f57cbcc
      Nick Piggin authored
      Rather than keep a d_mounted count in the dentry, set a dentry flag instead.
      The flag can be cleared by checking the hash table to see if there are any
      mounts left, which is not time critical because it is performed at detach time.
      
      The mounted state of a dentry is only used to speculatively take a look in the
      mount hash table if it is set -- before following the mount, vfsmount lock is
      taken and mount re-checked without races.
      
      This saves 4 bytes on 32-bit, nothing on 64-bit but it does provide a hole I
      might use later (and some configs have larger than 32-bit spinlocks which might
      make use of the hole).
      
      Autofs4 conversion and changelog by Ian Kent <raven@themaw.net>:
      In autofs4, when expring direct (or offset) mounts we need to ensure that we
      block user path walks into the autofs mount, which is covered by another mount.
      To do this we clear the mounted status so that follows stop before walking into
      the mount and are essentially blocked until the expire is completed. The
      automount daemon still finds the correct dentry for the umount due to the
      follow mount logic in fs/autofs4/root.c:autofs4_follow_link(), which is set as
      an inode operation for direct and offset mounts only and is called following
      the lookup that stopped at the covered mount.
      
      At the end of the expire the covering mount probably has gone away so the
      mounted status need not be restored. But we need to check this and only restore
      the mounted status if the expire failed.
      
      XXX: autofs may not work right if we have other mounts go over the top of it?
      Signed-off-by: default avatarNick Piggin <npiggin@kernel.dk>
      5f57cbcc