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authorLinus Torvalds <torvalds@linux-foundation.org>2020-01-28 09:33:25 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-01-28 09:33:25 -0800
commit2180f214f4a5d8e2d8b7138d9a59246ee05753b9 (patch)
treeaeb600fba396606e1998c34bb527d184b2b113c1 /kernel
parent634cd4b6afe15dca8df02bcba242b9b0c5e9b5a5 (diff)
parentf5bfdc8e3947a7ae489cf8ae9cfd6b3fb357b952 (diff)
Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar: "Just a handful of changes in this cycle: an ARM64 performance optimization, a comment fix and a debug output fix" * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: locking/osq: Use optimized spinning loop for arm64 locking/qspinlock: Fix inaccessible URL of MCS lock paper locking/lockdep: Fix lockdep_stats indentation problem
Diffstat (limited to 'kernel')
-rw-r--r--kernel/locking/lockdep_proc.c4
-rw-r--r--kernel/locking/osq_lock.c23
-rw-r--r--kernel/locking/qspinlock.c13
3 files changed, 19 insertions, 21 deletions
diff --git a/kernel/locking/lockdep_proc.c b/kernel/locking/lockdep_proc.c
index dadb7b7fba37..9bb6d2497b04 100644
--- a/kernel/locking/lockdep_proc.c
+++ b/kernel/locking/lockdep_proc.c
@@ -286,9 +286,9 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
seq_printf(m, " stack-trace entries: %11lu [max: %lu]\n",
nr_stack_trace_entries, MAX_STACK_TRACE_ENTRIES);
#if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING)
- seq_printf(m, " number of stack traces: %llu\n",
+ seq_printf(m, " number of stack traces: %11llu\n",
lockdep_stack_trace_count());
- seq_printf(m, " number of stack hash chains: %llu\n",
+ seq_printf(m, " number of stack hash chains: %11llu\n",
lockdep_stack_hash_count());
#endif
seq_printf(m, " combined max dependencies: %11u\n",
diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c
index 6ef600aa0f47..1f7734949ac8 100644
--- a/kernel/locking/osq_lock.c
+++ b/kernel/locking/osq_lock.c
@@ -134,20 +134,17 @@ bool osq_lock(struct optimistic_spin_queue *lock)
* cmpxchg in an attempt to undo our queueing.
*/
- while (!READ_ONCE(node->locked)) {
- /*
- * If we need to reschedule bail... so we can block.
- * Use vcpu_is_preempted() to avoid waiting for a preempted
- * lock holder:
- */
- if (need_resched() || vcpu_is_preempted(node_cpu(node->prev)))
- goto unqueue;
-
- cpu_relax();
- }
- return true;
+ /*
+ * Wait to acquire the lock or cancelation. Note that need_resched()
+ * will come with an IPI, which will wake smp_cond_load_relaxed() if it
+ * is implemented with a monitor-wait. vcpu_is_preempted() relies on
+ * polling, be careful.
+ */
+ if (smp_cond_load_relaxed(&node->locked, VAL || need_resched() ||
+ vcpu_is_preempted(node_cpu(node->prev))))
+ return true;
-unqueue:
+ /* unqueue */
/*
* Step - A -- stabilize @prev
*
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 2473f10c6956..b9515fcc9b29 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -31,14 +31,15 @@
/*
* The basic principle of a queue-based spinlock can best be understood
* by studying a classic queue-based spinlock implementation called the
- * MCS lock. The paper below provides a good description for this kind
- * of lock.
+ * MCS lock. A copy of the original MCS lock paper ("Algorithms for Scalable
+ * Synchronization on Shared-Memory Multiprocessors by Mellor-Crummey and
+ * Scott") is available at
*
- * http://www.cise.ufl.edu/tr/DOC/REP-1992-71.pdf
+ * https://bugzilla.kernel.org/show_bug.cgi?id=206115
*
- * This queued spinlock implementation is based on the MCS lock, however to make
- * it fit the 4 bytes we assume spinlock_t to be, and preserve its existing
- * API, we must modify it somehow.
+ * This queued spinlock implementation is based on the MCS lock, however to
+ * make it fit the 4 bytes we assume spinlock_t to be, and preserve its
+ * existing API, we must modify it somehow.
*
* In particular; where the traditional MCS lock consists of a tail pointer
* (8 bytes) and needs the next pointer (another 8 bytes) of its own node to