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Michel Lespinasse 70bdc6e064 rwsem: lighter active count checks when waking up readers 
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>
2010-08-09 20:45:10 -07:00
..
lzo lib: add support for LZO-compressed kernels 2010-01-11 09:34:04 -08:00
reed_solomon
zlib_deflate trivial: fix typo "to to" in multiple files 2009-09-21 15:14:55 +02:00
zlib_inflate inflate_fast: sout is already a short so ptr arith was off by one. 2010-03-12 15:52:44 -08:00
.gitignore
argv_split.c tree-wide: convert open calls to remove spaces to skip_spaces() lib function 2009-12-15 08:53:32 -08:00
atomic64.c lib: Fix atomic64_add_unless return value convention 2010-03-01 11:38:46 -08:00
atomic64_test.c ARM: 6213/1: atomic64_test: add ARM as supported architecture 2010-07-27 10:43:46 +01:00
audit.c
bcd.c rtc: BCD codeshrink 2008-07-24 10:47:33 -07:00
bitmap.c Revert "cpusets: randomize node rotor used in cpuset_mem_spread_node()" 2010-05-30 09:00:03 -07:00
bitrev.c
btree.c lib/btree: fix possible NULL pointer dereference 2010-05-15 12:48:10 -07:00
bug.c panic: Allow warnings to set different taint flags 2010-05-19 08:36:48 +01:00
bust_spinlocks.c oops handling: ensure that any oops is flushed to the mtdoops console 2009-01-06 15:59:11 -08:00
check_signature.c
checksum.c lib/checksum: fix one more thinko 2009-11-03 16:06:53 +01:00
cmdline.c generic, memparse(): constify argument 2008-07-28 15:05:23 +02:00
cpu-notifier-error-inject.c fault-injection: add CPU notifier error injection module 2010-05-27 09:12:48 -07:00
cpumask.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
crc-ccitt.c
crc-itu-t.c
crc-t10dif.c [SCSI] lib: Add support for the T10 (SCSI) Data Integrity Field CRC 2008-07-12 08:22:32 -05:00
crc7.c
crc16.c
crc32.c revert "crc32: use __BYTE_ORDER macro for endian detection" 2010-05-26 08:19:23 -07:00
crc32defs.h
ctype.c ctype: constify read-only _ctype string 2009-12-15 08:53:32 -08:00
debug_locks.c rcu: Introduce lockdep-based checking to RCU read-side primitives 2010-02-25 09:40:59 +01:00
debugobjects.c Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2010-05-18 08:17:58 -07:00
dec_and_lock.c atomic: only take lock when the counter drops to zero on UP as well 2009-06-16 19:47:47 -07:00
decompress.c Add LZO compression support for initramfs and old-style initrd 2010-01-11 09:34:05 -08:00
decompress_bunzip2.c bzip2: Add missing checks for malloc returning NULL 2009-12-15 14:04:19 -08:00
decompress_inflate.c lzma/gzip: fix potential oops when input data is truncated 2009-09-24 07:21:05 -07:00
decompress_unlzma.c lzma/gzip: fix potential oops when input data is truncated 2009-09-24 07:21:05 -07:00
decompress_unlzo.c lib: fix the use of LZO to decompress initramfs images 2010-04-24 11:31:25 -07:00
devres.c lib/devres.c: fix comment typo 2010-07-11 22:16:32 +02:00
div64.c
dma-debug.c dma-debug: Cleanup for copy-loop in filter_write() 2010-04-07 14:36:27 +02:00
dump_stack.c
dynamic_debug.c module: initialize module dynamic debug later 2010-07-04 20:17:22 -07:00
extable.c module: trim exception table on init free. 2009-06-12 21:47:04 +09:30
fault-inject.c headers: remove sched.h from interrupt.h 2009-10-11 11:20:58 -07:00
find_last_bit.c bitmap: find_last_bit() 2009-01-01 10:12:19 +10:30
find_next_bit.c
flex_array.c flex_array: add helpers to get and put to make pointers easy to use 2010-08-09 20:45:09 -07:00
gcd.c lib: add lib/gcd.c 2009-06-18 13:04:05 -07:00
gen_crc32table.c crc32: major optimization 2010-05-25 08:07:06 -07:00
genalloc.c genalloc: fix allocation from end of pool 2010-06-29 15:29:30 -07:00
halfmd4.c
hexdump.c lib: introduce common method to convert hex digits 2010-05-25 08:07:05 -07:00
hweight.c x86: Add optimized popcnt variants 2010-04-06 15:52:11 -07:00
idr.c idr: fix RCU lockdep splat in idr_get_next() 2010-06-23 06:50:45 -07:00
inflate.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
int_sqrt.c
iomap.c Use WARN() in lib/ 2008-07-26 12:00:07 -07:00
iomap_copy.c
iommu-helper.c iommu: inline iommu_num_pages 2010-08-09 20:45:05 -07:00
ioremap.c x86, ioremap: Fix incorrect physical address handling in PAE mode 2010-07-09 11:42:03 -07:00
irq_regs.c
is_single_threaded.c kernel: is_current_single_threaded: don't use ->mmap_sem 2009-07-17 09:11:31 +10:00
kasprintf.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
Kconfig lmb: rename to memblock 2010-07-14 17:14:00 +10:00
Kconfig.debug Merge git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core-2.6 2010-08-06 11:36:30 -07:00
Kconfig.kgdb mips,kgdb: kdb low level trap catch and stack trace 2010-05-20 21:04:26 -05:00
Kconfig.kmemcheck kmemcheck: depend on HAVE_ARCH_KMEMCHECK 2009-07-01 22:28:44 +02:00
kernel_lock.c bkl: Fixup core_lock fallout 2009-12-14 23:55:33 +01:00
klist.c driver core: Remove completion from struct klist_node 2009-01-06 10:44:30 -08:00
kobject.c sysfs: Comment sysfs directory tagging logic 2010-05-21 09:37:31 -07:00
kobject_uevent.c kobject: free memory if netlink_kernel_create() fails 2010-06-04 13:27:52 -07:00
kref.c kref: remove kref_set 2010-05-21 09:37:29 -07:00
lcm.c block: Fix overrun in lcm() and move it to lib 2010-03-15 12:47:59 +01:00
libcrc32c.c libcrc32c: Fix "crc32c undefined" compilation error 2008-12-25 11:01:42 +11:00
list_debug.c list debugging: warn when deleting a deleted entry 2010-08-09 20:45:08 -07:00
list_sort.c lib: revise list_sort() header comment 2010-03-06 11:26:35 -08:00
locking-selftest-hardirq.h
locking-selftest-mutex.h
locking-selftest-rlock-hardirq.h
locking-selftest-rlock-softirq.h
locking-selftest-rlock.h
locking-selftest-rsem.h
locking-selftest-softirq.h
locking-selftest-spin-hardirq.h
locking-selftest-spin-softirq.h
locking-selftest-spin.h
locking-selftest-wlock-hardirq.h
locking-selftest-wlock-softirq.h
locking-selftest-wlock.h
locking-selftest-wsem.h
locking-selftest.c locking: rename trace_softirq_[enter|exit] => lockdep_softirq_[enter|exit] 2009-03-13 01:32:36 +01:00
lru_cache.c The DRBD driver 2009-10-01 21:17:49 +02:00
Makefile lmb: rename to memblock 2010-07-14 17:14:00 +10:00
nlattr.c Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/kaber/nf-next-2.6 2009-03-26 22:45:23 -07:00
parser.c parser: remove unnecessary strlen() 2009-12-15 08:53:33 -08:00
percpu_counter.c tmpfs: add accurate compare function to percpu_counter library 2010-08-09 20:44:58 -07:00
plist.c plist: Make plist debugging raw_spinlock aware 2009-12-14 23:55:33 +01:00
prio_heap.c lib: fix sparse shadowed variable warning 2009-01-06 15:59:11 -08:00
prio_tree.c
proportions.c Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-01-06 17:10:04 -08:00
radix-tree.c radix-tree: omplement function radix_tree_range_tag_if_tagged 2010-08-09 20:44:59 -07:00
random32.c Merge branch 'master' into for-next 2010-06-16 18:08:13 +02:00
ratelimit.c ratelimit: fix the return value when __ratelimit() fails to acquire the lock 2010-04-07 08:38:04 -07:00
rational.c lib/rational.c needs module.h 2010-01-11 09:34:05 -08:00
rbtree.c rbtree: Undo augmented trees performance damage and regression 2010-07-05 14:43:50 +02:00
reciprocal_div.c
rwsem-spinlock.c rwsem generic spinlock: use IRQ save/restore spinlocks 2010-04-07 16:15:05 -07:00
rwsem.c rwsem: lighter active count checks when waking up readers 2010-08-09 20:45:10 -07:00
scatterlist.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
sha1.c
show_mem.c mm: use the same log level for show_mem() 2010-03-06 11:26:27 -08:00
smp_processor_id.c cpumask: convert lib/smp_processor_id to new cpumask ops 2009-01-30 15:47:34 +01:00
sort.c generic swap(): lib/sort.c: rename swap to swap_func 2009-01-08 08:31:14 -08:00
spinlock_debug.c locking: Further name space cleanups 2009-12-14 23:55:33 +01:00
string.c lib/string.c: simplify strnstr() 2010-03-06 11:26:35 -08:00
string_helpers.c [SCSI] lib: string_get_size(): don't hang on zero; no decimals on exact 2008-10-23 11:42:20 -05:00
swiotlb.c swiotlb: Make swiotlb bookkeeping functions visible in the header file. 2010-06-07 11:59:27 -04:00
syscall.c task_current_syscall 2008-07-26 12:00:10 -07:00
textsearch.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
ts_bm.c textsearch: ts_bm: support case insensitive searching in Boyer-Moore algorithm 2008-07-08 02:37:54 -07:00
ts_fsm.c textsearch: ts_fsm: return error on request for case insensitive search 2008-07-08 02:38:27 -07:00
ts_kmp.c textsearch: ts_kmp: support case insensitive searching in Knuth-Morris-Pratt algorithm 2008-07-08 02:38:09 -07:00
uuid.c Unified UUID/GUID definition 2010-05-19 22:40:47 -04:00
vsprintf.c lib: vsprintf: useless strlen() removed 2010-08-09 20:45:09 -07:00