The virtual console layer uses the BKL for various things that don't really
need it. Clean them out.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Pass down the ldisc number so that the drivers don't have to peek into the
tty object themselves. This lets us get rid of another case of back referencing
port to tty which we don't want (because of races versus hangup/close).
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
One or two drivers go poking back into the tty from the termios setting
routine in unsafe ways. We don't need to pass the tty down because the
[ab]users are just using it to get at things they can get at anyway.
This leaves low_latency setting to sort out along with set_ldisc use.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Make it robust against hang up events. In most cases we can do this simply
by passing the right things in the first place.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Use the port mutex and port lock to fix the various races. The locking
still isn't totally consistent but its better than before. Wants switching
to the port helpers.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This now refcounts but doesn't actually check the reference was obtained in
all the places it should.
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Use the port mutex instead
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
The lock is no longer needed for wait until sent paths so this can go
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This lets us avoid problems with races on the flag changes
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg 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: Dave Airlie <airlied@redhat.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: James Simmons <jsimmons@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg 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=17741
Signed-off-by: Howard Chu <hyc@symas.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
As Jeff Dike pointed out, the Hayes ESP driver was removed in commit
f53a2ade0b, 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: Greg Kroah-Hartman <gregkh@suse.de>
Remove Hayes ESP ioctls
The Hayes ESP driver has been removed from the tree:
commit f53a2ade0b
("tty: esp: remove broken driver")
so its ioctls aren't needed any more.
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg 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: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg 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: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg 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: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg 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: Feng Tang <feng.tang@intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg 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: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Greg 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: Christoph Egger <siccegge@cs.fau.de>
Acked-by: Greg Ungerer <gerg@snapgear.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
drivers/char/n_gsm.c: linux/timer.h is included more than once.
Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ecryptfs/ecryptfs-2.6:
ecryptfs: dont call lookup_one_len to avoid NULL nameidata
fs/ecryptfs/file.c: introduce missing free
ecryptfs: release reference to lower mount if interpose fails
eCryptfs: Handle ioctl calls with unlocked and compat functions
ecryptfs: Fix warning in ecryptfs_process_response()
* '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
These form the basis of the basic WRITE etc primitives, so we
need them to be always visible. Otherwise we see errors like:
mm/filemap.c:2164: error: 'REQ_WRITE' undeclared
fs/read_write.c:362: error: 'REQ_WRITE' undeclared
fs/splice.c:1108: error: 'REQ_WRITE' undeclared
fs/aio.c:1496: error: 'REQ_WRITE' undeclared
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This patch adds USB Vendor and Product ID for Pelican PL-3601 'TSZ'
Wired Xbox 360 Controller to the device table.
Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
"ret" should be signed here or the error handling doesn't work.
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
* 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
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: qiaochong <qiaochong@loongson.cn>
Cc: Greg KH <greg@kroah.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: qiaochong <qiaochong@loongson.cn>
Cc: Greg KH <greg@kroah.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Michel Lespinasse <walken@google.com>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Michel Lespinasse <walken@google.com>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Michel Lespinasse <walken@google.com>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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: Michel Lespinasse <walken@google.com>
Acked-by: David 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
