This now refcounts but doesn't actually check the reference was obtained in
all the places it should.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Use the port mutex instead
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The lock is no longer needed for wait until sent paths so this can go
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Use the port mutext for config setting, the rest is locked sufficiently
anyway that the BKL makes no odds.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

We don't need it while waiting and we can lock the ioctls using the port
mutex. While at it eliminate use of the hangup mutex and switch to the port
mutex.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

We can use the port mutex for this and also for the hangup path so removing
the problematic use of the hangup mutex in this driver. Fix up the locking
on the various port flags while we are at it.

Ultimately this driver needs to be using tty_port_ helpers which would sort
this out far better.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

As with the others we can use the port mutex to get the needed locking
properties and fix the race with open.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The riscom8 board uses lock_kernel to protect bits of the port setting
ioctl logic. We can use the port mutex for this as the logic is internal
and will also lock set versus open (a locking property that has been lost
somewhere along the way)
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This lets us avoid problems with races on the flag changes
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Remove unneeded tty layer lock kernel bits. Relock the needed bits using the
port mutex. The istallion still has brd state races but those are not new
or introduced by the removal of the lock_kernel logic.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Jesse's initial patch commit said:

"At panic time (i.e.  when oops_in_progress is set) we should try a bit
harder to update the screen and make sure output gets to the VT, since
some drivers are capable of flipping back to it.

So make sure we try to unblank and update the display if called from a
panic context."

I've enhanced this to add a flag to the vc that console layer can set to
indicate they want this behaviour to occur.  This also adds support to
fbcon for that flag and adds an fb flag for drivers to indicate they want
to use the support.  It enables this for KMS drivers.
Signed-off-by: NDave Airlie <airlied@redhat.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: NJames Simmons <jsimmons@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This patch is against the 2.6.34 source.

Paraphrased from the 1989 BSD patch by David Borman @ cray.com:

     These are the changes needed for the kernel to support
     LINEMODE in the server.

     There is a new bit in the termios local flag word, EXTPROC.
     When this bit is set, several aspects of the terminal driver
     are disabled.  Input line editing, character echo, and mapping
     of signals are all disabled.  This allows the telnetd to turn
     off these functions when in linemode, but still keep track of
     what state the user wants the terminal to be in.

     New ioctl:
         TIOCSIG         Generate a signal to processes in the
                         current process group of the pty.

     There is a new mode for packet driver, the TIOCPKT_IOCTL bit.
     When packet mode is turned on in the pty, and the EXTPROC bit
     is set, then whenever the state of the pty is changed, the
     next read on the master side of the pty will have the TIOCPKT_IOCTL
     bit set.  This allows the process on the server side of the pty
     to know when the state of the terminal has changed; it can then
     issue the appropriate ioctl to retrieve the new state.

Since the original BSD patches accompanied the source code for telnet
I've left that reference here, but obviously the feature is useful for
any remote terminal protocol, including ssh.

The corresponding feature has existed in the BSD tty driver since 1989.
For historical reference, a good copy of the relevant files can be found
here:

http://anonsvn.mit.edu/viewvc/krb5/trunk/src/appl/telnet/?pathrev=17741Signed-off-by: NHoward Chu <hyc@symas.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

As Jeff Dike pointed out, the Hayes ESP driver was removed in commit
f53a2ade, so these ioctl definitions
should also be removed.  This cleans up the remaining arch-specific
locations of this ioctl value.

Thanks to Arnd for pointing these out.

Cc: Jeff Dike <jdike@addtoit.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Remove Hayes ESP ioctls

The Hayes ESP driver has been removed from the tree:
commit f53a2ade
("tty: esp: remove broken driver")
so its ioctls aren't needed any more.
Signed-off-by: NJeff Dike <jdike@linux.intel.com>
Acked-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The mrst_max3110 driver had a set of unsafe wakeup sequences
along the following line:

if (!atomic_read(&foo)) {
  atomic_set(&foo, 1);
  wake_up(worker_thread);
}
and the worker thread would do

if (atomic_read(&foo)) {
  do_work();
  atomic_set(&foo, 0);
}

which can result in various missed wakups due to test-then-set races,
as well as due to clear-after-work instead of clear-before-work.

This patch fixes these races by using the proper bit test-and-set operations,
and by doing clear-before-work.
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

The mrst_max3110.c driver uses an open coded, non atomic variable
to create exclusion between two of its worker threads. More than that,
while the main thread does a proper set-work-clear sequence,
the other thread only does a test, with the result that no actual
exclusion is happening.

this patch replaces this open coded variable with a proper mutex

in addition, the 'lock' spinlock is removed from the per adapter structure,
the lock was only ever initialized but never used
Signed-off-by: NArjan van de Ven <arjan@linux.intel.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

MAX3111 is the SPI/UART IC installed on the MRST SPI Port Card as a serial
debug goal, and the SPI Port Card will be frequently mounted and unmounted
from the main board by developers depending whether debug serial is
required or not.

As the MAX3111 has no subvendor or product id registers available, the patch
will try to access one register to decide if this IC is present or not.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

This driver enable the max3110 device, it can be used as
a system console. the IRQ needs be enabled if user want a
better performance. MRST max3110 works in 3.684MHz clock,
which supports 230400 as its maximum rate.
Signed-off-by: NFeng Tang <feng.tang@intel.com>
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Adding UART_CAP_EFR and UART_CAP_SLEEP flags will enable sleep mode
and automatic CTS flow control for 16C950 UARTs. It will also avoid
capabilities detection warning like this:

"ttyS0: detected caps 00000700 should be 00000100"
Signed-off-by: NYegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

Signed-off-by: NAndy Shevchenko <ext-andriy.shevchenko@nokia.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

as there's no config CONSOLE (never has been as far as I can tell) and
noone has ever missed that piece of code, it should be safe to remove
it making the kernel a tiny bit less complex.
Signed-off-by: NChristoph Egger <siccegge@cs.fau.de>
Acked-by: NGreg Ungerer <gerg@snapgear.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/char/n_gsm.c: linux/timer.h is included more than once.
Signed-off-by: NAndrea Gelmini <andrea.gelmini@gelma.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

* 'writable_limits' of git://decibel.fi.muni.cz/~xslaby/linux:
  unistd: add __NR_prlimit64 syscall numbers
  rlimits: implement prlimit64 syscall
  rlimits: switch more rlimit syscalls to do_prlimit
  rlimits: redo do_setrlimit to more generic do_prlimit
  rlimits: add rlimit64 structure
  rlimits: do security check under task_lock
  rlimits: allow setrlimit to non-current tasks
  rlimits: split sys_setrlimit
  rlimits: selinux, do rlimits changes under task_lock
  rlimits: make sure ->rlim_max never grows in sys_setrlimit
  rlimits: add task_struct to update_rlimit_cpu
  rlimits: security, add task_struct to setrlimit

Fix up various system call number conflicts.  We not only added fanotify
system calls in the meantime, but asm-generic/unistd.h added a wait4
along with a range of reserved per-architecture system calls.

* git://git.infradead.org/mtd-2.6: (79 commits)
  mtd: Remove obsolete <mtd/compatmac.h> include
  mtd: Update copyright notices
  jffs2: Update copyright notices
  mtd-physmap: add support users can assign the probe type in board files
  mtd: remove redwood map driver
  mxc_nand: Add v3 (i.MX51) Support
  mxc_nand: support 8bit ecc
  mxc_nand: fix correct_data function
  mxc_nand: add V1_V2 namespace to registers
  mxc_nand: factor out a check_int function
  mxc_nand: make some internally used functions overwriteable
  mxc_nand: rework get_dev_status
  mxc_nand: remove 0xe00 offset from registers
  mtd: denali: Add multi connected NAND support
  mtd: denali: Remove set_ecc_config function
  mtd: denali: Remove unuseful code in get_xx_nand_para functions
  mtd: denali: Remove device_info_tag structure
  mtd: m25p80: add support for the Winbond W25Q32 SPI flash chip
  mtd: m25p80: add support for the Intel/Numonyx {16,32,64}0S33B SPI flash chips
  mtd: m25p80: add support for the EON EN25P{32, 64} SPI flash chips
  ...

Fix up trivial conflicts in drivers/mtd/maps/{Kconfig,redwood.c} due to
redwood driver removal.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/bcopeland/omfs:
  omfs: fix uninitialized variable warning
  omfs: sanity check cluster size
  omfs: refuse to mount if bitmap pointer is obviously wrong
  omfs: check bounds on block numbers before passing to sb_bread
  omfs: fix memory leak

* 'for-linus' of git://git.infradead.org/users/eparis/notify: (132 commits)
  fanotify: use both marks when possible
  fsnotify: pass both the vfsmount mark and inode mark
  fsnotify: walk the inode and vfsmount lists simultaneously
  fsnotify: rework ignored mark flushing
  fsnotify: remove global fsnotify groups lists
  fsnotify: remove group->mask
  fsnotify: remove the global masks
  fsnotify: cleanup should_send_event
  fanotify: use the mark in handler functions
  audit: use the mark in handler functions
  dnotify: use the mark in handler functions
  inotify: use the mark in handler functions
  fsnotify: send fsnotify_mark to groups in event handling functions
  fsnotify: Exchange list heads instead of moving elements
  fsnotify: srcu to protect read side of inode and vfsmount locks
  fsnotify: use an explicit flag to indicate fsnotify_destroy_mark has been called
  fsnotify: use _rcu functions for mark list traversal
  fsnotify: place marks on object in order of group memory address
  vfs/fsnotify: fsnotify_close can delay the final work in fput
  fsnotify: store struct file not struct path
  ...

Fix up trivial delete/modify conflict in fs/notify/inotify/inotify.c.

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs-2.6: (96 commits)
  no need for list_for_each_entry_safe()/resetting with superblock list
  Fix sget() race with failing mount
  vfs: don't hold s_umount over close_bdev_exclusive() call
  sysv: do not mark superblock dirty on remount
  sysv: do not mark superblock dirty on mount
  btrfs: remove junk sb_dirt change
  BFS: clean up the superblock usage
  AFFS: wait for sb synchronization when needed
  AFFS: clean up dirty flag usage
  cifs: truncate fallout
  mbcache: fix shrinker function return value
  mbcache: Remove unused features
  add f_flags to struct statfs(64)
  pass a struct path to vfs_statfs
  update VFS documentation for method changes.
  All filesystems that need invalidate_inode_buffers() are doing that explicitly
  convert remaining ->clear_inode() to ->evict_inode()
  Make ->drop_inode() just return whether inode needs to be dropped
  fs/inode.c:clear_inode() is gone
  fs/inode.c:evict() doesn't care about delete vs. non-delete paths now
  ...

Fix up trivial conflicts in fs/nilfs2/super.c

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6: (59 commits)
  igbvf.txt: Add igbvf Documentation
  igb.txt: Add igb documentation
  e100/e1000*/igb*/ixgb*: Add missing read memory barrier
  ixgbe: fix build error with FCOE_CONFIG without DCB_CONFIG
  netxen: protect tx timeout recovery by rtnl lock
  isdn: gigaset: use after free
  isdn: gigaset: add missing unlock
  solos-pci: Fix race condition in tasklet RX handling
  pkt_sched: Fix sch_sfq vs tcf_bind_filter oops
  net: disable preemption before call smp_processor_id()
  tcp: no md5sig option size check bug
  iwlwifi: fix locking assertions
  iwlwifi: fix TX tracer
  isdn: fix information leak
  net: Fix napi_gro_frags vs netpoll path
  usbnet: remove noisy and hardly useful printk
  rtl8180: avoid potential NULL deref in rtl8180_beacon_work
  ath9k: Remove myself from the MAINTAINERS list
  libertas: scan before assocation if no BSSID was given
  libertas: fix association with some APs by using extended rates
  ...

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/ide-2.6:
  tx493xide: use min_t() macro instead of min()
  drivers/ide: Use memdup_user
  via82cxxx: fix typo for VT6415 PCIE PATA IDE Host Controller support.
  ide-cd: Do not access completed requests in the irq handler

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc-2.6:
  sparc64: Update defconfig.
  sparc: Kill user copy check code.
  sparc64: Fix perf_arch_get_caller_regs().
  sparc64: Add missing ID to parport probing code.

* 'rs485fix' of git://www.jni.nu/cris:
  CRIS: ioctl for getting RS485 information

* 'merge' of git://git.kernel.org/pub/scm/linux/kernel/git/benh/powerpc:
  powerpc: fix build with make 3.82
  Revert "Input: appletouch - fix integer overflow issue"
  memblock: Fix memblock_is_region_reserved() to return a boolean
  powerpc: Trim defconfigs
  powerpc: fix i8042 module build error
  sound/soc: mpc5200_psc_ac97: Use gpio pins for cold reset
  powerpc/5200: add mpc5200_psc_ac97_gpio_reset

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/vapier/blackfin: (32 commits)
  Blackfin: gpio: add a debounce stub
  Blackfin: update defconfigs
  Blackfin: remove CONFIG_MEM_GENERIC_BOARD
  Blackfin: dpmc: punt unnecessary RTC_ISTAT clearing
  Blackfin: unify rotary encoder bitmasks
  Blackfin: unify SDH/RSI bitmasks
  Blackfin: BF54x: tweak DMAC MMR naming to match other ports
  Blackfin: TWI: clean up the MMR names
  Blackfin: add EVT_OVERRIDE/IPRIO core MMR helpers
  Blackfin: add support for dynamic ftrace
  Blackfin: add support for LZO compressed kernels
  Blackfin: portmux: fix peripheral map overflow when requesting pins
  Blackfin: document SPI CS limitations with CPHA=0
  Blackfin: remove useless and outdated documentation
  Blackfin: BF51x/BF52x: support GPIO Hysteresis/Schmitt Trigger options
  Blackfin: gpio/portmux: clean up whitespace corruption
  Blackfin: make sure mmiowb inserts a write barrier with SSYNC
  Blackfin: fix DMA/cache bug when resuming from suspend to RAM
  Blackfin: BF51x: fix handling of PH8 (the "internal" SPI0SEL4 pin)
  Blackfin: add a GPIO_DEFAULT_BOOT_SPI_CS
  ...

* 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/djbw/async_tx: (30 commits)
  DMAENGINE: at_hdmac: locking fixlet
  DMAENGINE: pch_dma: kill another usage of __raw_{read|write}l
  dma: dmatest: fix potential sign bug
  ioat2: catch and recover from broken vtd configurations v6
  DMAENGINE: add runtime slave control to COH 901 318 v3
  DMAENGINE: add runtime slave config to DMA40 v3
  DMAENGINE: generic slave channel control v3
  dmaengine: Driver for Topcliff PCH DMA controller
  intel_mid: Add Mrst & Mfld DMA Drivers
  drivers/dma: Eliminate a NULL pointer dereference
  dma/timb_dma: compile warning on 32 bit
  DMAENGINE: ste_dma40: support older silicon
  DMAENGINE: ste_dma40: support disabling physical channels
  DMAENGINE: ste_dma40: no disabled phy channels on ux500
  DMAENGINE: ste_dma40: fix suspend bug
  DMAENGINE: ste_dma40: add DB8500 memcpy channels
  DMAENGINE: ste_dma40: no flow control on memcpy
  DMAENGINE: ste_dma40: arch updates for LCLA and LCPA
  DMAENGINE: ste_dma40: allocate LCLA dynamically
  DMAENGINE: ste_dma40: no premature stop
  ...

Fix up trivial conflicts in arch/arm/mach-ux500/devices-db8500.c

According include/linux/console_struct.h,vc_scr_end is unsigned long.

struct vc_data {
    unsigned short  vc_num;         /* Console number */
    unsigned int    vc_cols;        /* [#] Console size */
    unsigned int    vc_rows;
    unsigned int    vc_size_row;        /* Bytes per row */
    unsigned int    vc_scan_lines;      /* # of scan lines */
    unsigned long   vc_origin;      /* [!] Start of real screen */
    unsigned long   vc_scr_end;     /* [!] End of real screen */
    unsigned long   vc_visible_origin;  /* [!] Top of visible window */
    unsigned int    vc_top, vc_bottom;  /* Scrolling region */
    const struct consw *vc_sw;
    unsigned short  *vc_screenbuf;
...
}
Signed-off-by: Nqiaochong <qiaochong@loongson.cn>
Cc: Greg KH <greg@kroah.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel will die on some platform when switch from vga mode to framebuffer
mode.  The reason of this bug is that bind_con_driver reset vc->vc_origin
to (unsigned long)vc->vc_screenbuf.

On vgacon vc->vc_origin is not releated to vc->vc_screenbuf,if set
vc->vc_origin to vc->vc_screenbuf,kernel will die on vc_do_resize.

static int vc_do_resize(struct tty_struct *tty, struct tty_struct *real_tty,
        struct vc_data *vc, unsigned int cols, unsigned int lines)
{
    unsigned long old_origin, new_origin, new_scr_end, rlth, rrem, err = 0;
    unsigned int old_cols, old_rows, old_row_size, old_screen_size;
    unsigned int new_cols, new_rows, new_row_size, new_screen_size;
    unsigned int end, user;
...
        end = (old_rows > new_rows) ? old_origin +
            (old_row_size * new_rows) :
            vc->vc_scr_end;

...
/*
here for a test from vgacon to framebuffer:
old_origin=0x810814a0,end=0xb00b8fa0,vc->vc_origin=0x810814a0
the code bellow will copy memory from 0x810814a0 to 0xb00b8fa0,
this will cover kernel code,kernel died here.
*/

    while (old_origin < end) {

        scr_memcpyw((unsigned short *) new_origin,
                (unsigned short *) old_origin, rlth);
        if (rrem)
            scr_memsetw((void *)(new_origin + rlth),
                    vc->vc_video_erase_char, rrem);
        old_origin += old_row_size;
        new_origin += new_row_size;
    }

...
}

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Nqiaochong <qiaochong@loongson.cn>
Cc: Greg KH <greg@kroah.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

More code can be pushed from rwsem_down_read_failed and
rwsem_down_write_failed into rwsem_down_failed_common.

Following change adding down_read_critical infrastructure support also
enjoys having flags available in a register rather than having to fish it
out in the struct rwsem_waiter...
Signed-off-by: NMichel Lespinasse <walken@google.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This change addresses the following situation:

- Thread A acquires the rwsem for read
- Thread B tries to acquire the rwsem for write, notices there is already
  an active owner for the rwsem.
- Thread C tries to acquire the rwsem for read, notices that thread B already
  tried to acquire it.
- Thread C grabs the spinlock and queues itself on the wait queue.
- Thread B grabs the spinlock and queues itself behind C. At this point A is
  the only remaining active owner on the rwsem.

In this situation thread B could notice that it was the last active writer
on the rwsem, and decide to wake C to let it proceed in parallel with A
since they both only want the rwsem for read.
Signed-off-by: NMichel Lespinasse <walken@google.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Previously each waiting thread added a bias of RWSEM_WAITING_BIAS.  With
this change, the bias is added only once to indicate that the wait list is
non-empty.

This has a few nice properties which will be used in following changes:
- when the spinlock is held and the waiter list is known to be non-empty,
  count < RWSEM_WAITING_BIAS  <=>  there is an active writer on that sem
- count == RWSEM_WAITING_BIAS  <=>  there are waiting threads and no
                                     active readers/writers on that sem
Signed-off-by: NMichel Lespinasse <walken@google.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In __rwsem_do_wake(), we can skip the active count check unless we come
there from up_xxxx().  Also when checking the active count, it is not
actually necessary to increment it; this allows us to get rid of the read
side undo code and simplify the calculation of the final rwsem count
adjustment once we've counted the reader threads to wake.

The basic observation is the following.  When there are waiter threads on
a rwsem and the spinlock is held, other threads can only increment the
active count by trying to grab the rwsem in down_xxxx().  However
down_xxxx() will notice there are waiter threads and take the down_failed
path, blocking to acquire the spinlock on the way there.  Therefore, a
thread observing an active count of zero with waiters queued and the
spinlock held, is protected against other threads acquiring the rwsem
until it wakes the last waiter or releases the spinlock.
Signed-off-by: NMichel Lespinasse <walken@google.com>
Acked-by: NDavid Howells <dhowells@redhat.com>
Cc: Mike Waychison <mikew@google.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>