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authorLinus Torvalds <torvalds@linux-foundation.org>2014-06-03 12:57:53 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-06-03 12:57:53 -0700
commit776edb59317ada867dfcddde40b55648beeb0078 (patch)
treef6a6136374642323cfefd7d6399ea429f9018ade /kernel/locking
parent59a3d4c3631e553357b7305dc09db1990aa6757c (diff)
parent3cf2f34e1a3d4d5ff209d087925cf950e52f4805 (diff)
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Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip into next
Pull core locking updates from Ingo Molnar: "The main changes in this cycle were: - reduced/streamlined smp_mb__*() interface that allows more usecases and makes the existing ones less buggy, especially in rarer architectures - add rwsem implementation comments - bump up lockdep limits" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (33 commits) rwsem: Add comments to explain the meaning of the rwsem's count field lockdep: Increase static allocations arch: Mass conversion of smp_mb__*() arch,doc: Convert smp_mb__*() arch,xtensa: Convert smp_mb__*() arch,x86: Convert smp_mb__*() arch,tile: Convert smp_mb__*() arch,sparc: Convert smp_mb__*() arch,sh: Convert smp_mb__*() arch,score: Convert smp_mb__*() arch,s390: Convert smp_mb__*() arch,powerpc: Convert smp_mb__*() arch,parisc: Convert smp_mb__*() arch,openrisc: Convert smp_mb__*() arch,mn10300: Convert smp_mb__*() arch,mips: Convert smp_mb__*() arch,metag: Convert smp_mb__*() arch,m68k: Convert smp_mb__*() arch,m32r: Convert smp_mb__*() arch,ia64: Convert smp_mb__*() ...
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/lockdep_internals.h6
-rw-r--r--kernel/locking/rwsem-xadd.c49
2 files changed, 52 insertions, 3 deletions
diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h
index 4f560cfedc8f..51c4b24b6328 100644
--- a/kernel/locking/lockdep_internals.h
+++ b/kernel/locking/lockdep_internals.h
@@ -54,9 +54,9 @@ enum {
* table (if it's not there yet), and we check it for lock order
* conflicts and deadlocks.
*/
-#define MAX_LOCKDEP_ENTRIES 16384UL
+#define MAX_LOCKDEP_ENTRIES 32768UL
-#define MAX_LOCKDEP_CHAINS_BITS 15
+#define MAX_LOCKDEP_CHAINS_BITS 16
#define MAX_LOCKDEP_CHAINS (1UL << MAX_LOCKDEP_CHAINS_BITS)
#define MAX_LOCKDEP_CHAIN_HLOCKS (MAX_LOCKDEP_CHAINS*5)
@@ -65,7 +65,7 @@ enum {
* Stack-trace: tightly packed array of stack backtrace
* addresses. Protected by the hash_lock.
*/
-#define MAX_STACK_TRACE_ENTRIES 262144UL
+#define MAX_STACK_TRACE_ENTRIES 524288UL
extern struct list_head all_lock_classes;
extern struct lock_chain lock_chains[];
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index 1d66e08e897d..b4219ff87b8c 100644
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -12,6 +12,55 @@
#include <linux/export.h>
/*
+ * Guide to the rw_semaphore's count field for common values.
+ * (32-bit case illustrated, similar for 64-bit)
+ *
+ * 0x0000000X (1) X readers active or attempting lock, no writer waiting
+ * X = #active_readers + #readers attempting to lock
+ * (X*ACTIVE_BIAS)
+ *
+ * 0x00000000 rwsem is unlocked, and no one is waiting for the lock or
+ * attempting to read lock or write lock.
+ *
+ * 0xffff000X (1) X readers active or attempting lock, with waiters for lock
+ * X = #active readers + # readers attempting lock
+ * (X*ACTIVE_BIAS + WAITING_BIAS)
+ * (2) 1 writer attempting lock, no waiters for lock
+ * X-1 = #active readers + #readers attempting lock
+ * ((X-1)*ACTIVE_BIAS + ACTIVE_WRITE_BIAS)
+ * (3) 1 writer active, no waiters for lock
+ * X-1 = #active readers + #readers attempting lock
+ * ((X-1)*ACTIVE_BIAS + ACTIVE_WRITE_BIAS)
+ *
+ * 0xffff0001 (1) 1 reader active or attempting lock, waiters for lock
+ * (WAITING_BIAS + ACTIVE_BIAS)
+ * (2) 1 writer active or attempting lock, no waiters for lock
+ * (ACTIVE_WRITE_BIAS)
+ *
+ * 0xffff0000 (1) There are writers or readers queued but none active
+ * or in the process of attempting lock.
+ * (WAITING_BIAS)
+ * Note: writer can attempt to steal lock for this count by adding
+ * ACTIVE_WRITE_BIAS in cmpxchg and checking the old count
+ *
+ * 0xfffe0001 (1) 1 writer active, or attempting lock. Waiters on queue.
+ * (ACTIVE_WRITE_BIAS + WAITING_BIAS)
+ *
+ * Note: Readers attempt to lock by adding ACTIVE_BIAS in down_read and checking
+ * the count becomes more than 0 for successful lock acquisition,
+ * i.e. the case where there are only readers or nobody has lock.
+ * (1st and 2nd case above).
+ *
+ * Writers attempt to lock by adding ACTIVE_WRITE_BIAS in down_write and
+ * checking the count becomes ACTIVE_WRITE_BIAS for successful lock
+ * acquisition (i.e. nobody else has lock or attempts lock). If
+ * unsuccessful, in rwsem_down_write_failed, we'll check to see if there
+ * are only waiters but none active (5th case above), and attempt to
+ * steal the lock.
+ *
+ */
+
+/*
* Initialize an rwsem:
*/
void __init_rwsem(struct rw_semaphore *sem, const char *name,