1 files changed, 132 insertions, 8 deletions

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 2cecf05c82fd..60e800e0b5a0 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -15,8 +15,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
 
+#include <linux/sched.h>
 #include <linux/random.h>
 #include <linux/sbitmap.h>
+#include <linux/seq_file.h>
 
 int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
 		      gfp_t flags, int node)
@@ -180,6 +182,62 @@ unsigned int sbitmap_weight(const struct sbitmap *sb)
 }
 EXPORT_SYMBOL_GPL(sbitmap_weight);
 
+void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
+{
+	seq_printf(m, "depth=%u\n", sb->depth);
+	seq_printf(m, "busy=%u\n", sbitmap_weight(sb));
+	seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
+	seq_printf(m, "map_nr=%u\n", sb->map_nr);
+}
+EXPORT_SYMBOL_GPL(sbitmap_show);
+
+static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
+{
+	if ((offset & 0xf) == 0) {
+		if (offset != 0)
+			seq_putc(m, '\n');
+		seq_printf(m, "%08x:", offset);
+	}
+	if ((offset & 0x1) == 0)
+		seq_putc(m, ' ');
+	seq_printf(m, "%02x", byte);
+}
+
+void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
+{
+	u8 byte = 0;
+	unsigned int byte_bits = 0;
+	unsigned int offset = 0;
+	int i;
+
+	for (i = 0; i < sb->map_nr; i++) {
+		unsigned long word = READ_ONCE(sb->map[i].word);
+		unsigned int word_bits = READ_ONCE(sb->map[i].depth);
+
+		while (word_bits > 0) {
+			unsigned int bits = min(8 - byte_bits, word_bits);
+
+			byte |= (word & (BIT(bits) - 1)) << byte_bits;
+			byte_bits += bits;
+			if (byte_bits == 8) {
+				emit_byte(m, offset, byte);
+				byte = 0;
+				byte_bits = 0;
+				offset++;
+			}
+			word >>= bits;
+			word_bits -= bits;
+		}
+	}
+	if (byte_bits) {
+		emit_byte(m, offset, byte);
+		offset++;
+	}
+	if (offset)
+		seq_putc(m, '\n');
+}
+EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);
+
 static unsigned int sbq_calc_wake_batch(unsigned int depth)
 {
 	unsigned int wake_batch;
@@ -239,7 +297,19 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);
 
 void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
 {
-	sbq->wake_batch = sbq_calc_wake_batch(depth);
+	unsigned int wake_batch = sbq_calc_wake_batch(depth);
+	int i;
+
+	if (sbq->wake_batch != wake_batch) {
+		WRITE_ONCE(sbq->wake_batch, wake_batch);
+		/*
+		 * Pairs with the memory barrier in sbq_wake_up() to ensure that
+		 * the batch size is updated before the wait counts.
+		 */
+		smp_mb__before_atomic();
+		for (i = 0; i < SBQ_WAIT_QUEUES; i++)
+			atomic_set(&sbq->ws[i].wait_cnt, 1);
+	}
 	sbitmap_resize(&sbq->sb, depth);
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_resize);
@@ -297,20 +367,39 @@ static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
 static void sbq_wake_up(struct sbitmap_queue *sbq)
 {
 	struct sbq_wait_state *ws;
+	unsigned int wake_batch;
 	int wait_cnt;
 
-	/* Ensure that the wait list checks occur after clear_bit(). */
-	smp_mb();
+	/*
+	 * Pairs with the memory barrier in set_current_state() to ensure the
+	 * proper ordering of clear_bit()/waitqueue_active() in the waker and
+	 * test_and_set_bit()/prepare_to_wait()/finish_wait() in the waiter. See
+	 * the comment on waitqueue_active(). This is __after_atomic because we
+	 * just did clear_bit() in the caller.
+	 */
+	smp_mb__after_atomic();
 
 	ws = sbq_wake_ptr(sbq);
 	if (!ws)
 		return;
 
 	wait_cnt = atomic_dec_return(&ws->wait_cnt);
-	if (unlikely(wait_cnt < 0))
-		wait_cnt = atomic_inc_return(&ws->wait_cnt);
-	if (wait_cnt == 0) {
-		atomic_add(sbq->wake_batch, &ws->wait_cnt);
+	if (wait_cnt <= 0) {
+		wake_batch = READ_ONCE(sbq->wake_batch);
+		/*
+		 * Pairs with the memory barrier in sbitmap_queue_resize() to
+		 * ensure that we see the batch size update before the wait
+		 * count is reset.
+		 */
+		smp_mb__before_atomic();
+		/*
+		 * If there are concurrent callers to sbq_wake_up(), the last
+		 * one to decrement the wait count below zero will bump it back
+		 * up. If there is a concurrent resize, the count reset will
+		 * either cause the cmpxchg to fail or overwrite after the
+		 * cmpxchg.
+		 */
+		atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wait_cnt + wake_batch);
 		sbq_index_atomic_inc(&sbq->wake_index);
 		wake_up(&ws->wait);
 	}
@@ -331,7 +420,8 @@ void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 	int i, wake_index;
 
 	/*
-	 * Make sure all changes prior to this are visible from other CPUs.
+	 * Pairs with the memory barrier in set_current_state() like in
+	 * sbq_wake_up().
 	 */
 	smp_mb();
 	wake_index = atomic_read(&sbq->wake_index);
@@ -345,3 +435,37 @@ void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
 	}
 }
 EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);
+
+void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
+{
+	bool first;
+	int i;
+
+	sbitmap_show(&sbq->sb, m);
+
+	seq_puts(m, "alloc_hint={");
+	first = true;
+	for_each_possible_cpu(i) {
+		if (!first)
+			seq_puts(m, ", ");
+		first = false;
+		seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
+	}
+	seq_puts(m, "}\n");
+
+	seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
+	seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
+
+	seq_puts(m, "ws={\n");
+	for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
+		struct sbq_wait_state *ws = &sbq->ws[i];
+
+		seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
+			   atomic_read(&ws->wait_cnt),
+			   waitqueue_active(&ws->wait) ? "active" : "inactive");
+	}
+	seq_puts(m, "}\n");
+
+	seq_printf(m, "round_robin=%d\n", sbq->round_robin);
+}
+EXPORT_SYMBOL_GPL(sbitmap_queue_show);