From e3e84f62054c6072a9c7438fb2880a2db88159d4 Mon Sep 17 00:00:00 2001
From: Greg Kroah-Hartman <gregkh@google.com>
Date: Thu, 12 Sep 2024 06:34:05 +0000
Subject: [PATCH] Revert "sbitmap: fix io hung due to race on
 sbitmap_word::cleared"

This reverts commit 681583ad673186b5dec793f4b8c4f1dd242b89a5 which is
commit 72d04bdcf3f7d7e07d82f9757946f68802a7270a upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I6c645c8b4a157820561507a1cf3c1180b94aebff
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
---
 include/linux/sbitmap.h |  5 -----
 lib/sbitmap.c           | 36 +++++++-----------------------------
 2 files changed, 7 insertions(+), 34 deletions(-)

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index c09cdcc99471..d662cf136021 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -36,11 +36,6 @@ struct sbitmap_word {
 	 * @cleared: word holding cleared bits
 	 */
 	unsigned long cleared ____cacheline_aligned_in_smp;
-
-	/**
-	 * @swap_lock: serializes simultaneous updates of ->word and ->cleared
-	 */
-	spinlock_t swap_lock;
 } ____cacheline_aligned_in_smp;
 
 /**
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 61075535a807..a727d0b12763 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -60,30 +60,12 @@ static inline void update_alloc_hint_after_get(struct sbitmap *sb,
 /*
  * See if we have deferred clears that we can batch move
  */
-static inline bool sbitmap_deferred_clear(struct sbitmap_word *map,
-		unsigned int depth, unsigned int alloc_hint, bool wrap)
+static inline bool sbitmap_deferred_clear(struct sbitmap_word *map)
 {
-	unsigned long mask, word_mask;
+	unsigned long mask;
 
-	guard(spinlock_irqsave)(&map->swap_lock);
-
-	if (!map->cleared) {
-		if (depth == 0)
-			return false;
-
-		word_mask = (~0UL) >> (BITS_PER_LONG - depth);
-		/*
-		 * The current behavior is to always retry after moving
-		 * ->cleared to word, and we change it to retry in case
-		 * of any free bits. To avoid an infinite loop, we need
-		 * to take wrap & alloc_hint into account, otherwise a
-		 * soft lockup may occur.
-		 */
-		if (!wrap && alloc_hint)
-			word_mask &= ~((1UL << alloc_hint) - 1);
-
-		return (READ_ONCE(map->word) & word_mask) != word_mask;
-	}
+	if (!READ_ONCE(map->cleared))
+		return false;
 
 	/*
 	 * First get a stable cleared mask, setting the old mask to 0.
@@ -103,7 +85,6 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
 		      bool alloc_hint)
 {
 	unsigned int bits_per_word;
-	int i;
 
 	if (shift < 0)
 		shift = sbitmap_calculate_shift(depth);
@@ -135,9 +116,6 @@ int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
 		return -ENOMEM;
 	}
 
-	for (i = 0; i < sb->map_nr; i++)
-		spin_lock_init(&sb->map[i].swap_lock);
-
 	return 0;
 }
 EXPORT_SYMBOL_GPL(sbitmap_init_node);
@@ -148,7 +126,7 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
 	unsigned int i;
 
 	for (i = 0; i < sb->map_nr; i++)
-		sbitmap_deferred_clear(&sb->map[i], 0, 0, 0);
+		sbitmap_deferred_clear(&sb->map[i]);
 
 	sb->depth = depth;
 	sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);
@@ -201,7 +179,7 @@ static int sbitmap_find_bit_in_word(struct sbitmap_word *map,
 					alloc_hint, wrap);
 		if (nr != -1)
 			break;
-		if (!sbitmap_deferred_clear(map, depth, alloc_hint, wrap))
+		if (!sbitmap_deferred_clear(map))
 			break;
 	} while (1);
 
@@ -527,7 +505,7 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
 		unsigned int map_depth = __map_depth(sb, index);
 		unsigned long val;
 
-		sbitmap_deferred_clear(map, 0, 0, 0);
+		sbitmap_deferred_clear(map);
 		val = READ_ONCE(map->word);
 		if (val == (1UL << (map_depth - 1)) - 1)
 			goto next;