netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 175 insertions, 0 deletions

diff --git a/drivers/base/regmap/regcache-flat.c b/drivers/base/regmap/regcache-flat.c
new file mode 100644
index 000000000..be8497fd2
--- /dev/null
+++ b/drivers/base/regmap/regcache-flat.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0
+//
+// Register cache access API - flat caching support
+//
+// Copyright 2012 Wolfson Microelectronics plc
+//
+// Author: Mark Brown <broonie@opensource.wolfsonmicro.com>
+
+#include <linux/bitmap.h>
+#include <linux/bitops.h>
+#include <linux/device.h>
+#include <linux/limits.h>
+#include <linux/overflow.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+
+#include "internal.h"
+
+static inline unsigned int regcache_flat_get_index(const struct regmap *map,
+						   unsigned int reg)
+{
+	return regcache_get_index_by_order(map, reg);
+}
+
+struct regcache_flat_data {
+	unsigned long *valid;
+	unsigned int data[];
+};
+
+static int regcache_flat_init(struct regmap *map)
+{
+	unsigned int cache_size;
+	struct regcache_flat_data *cache;
+
+	if (!map || map->reg_stride_order < 0 || !map->max_register_is_set)
+		return -EINVAL;
+
+	cache_size = regcache_flat_get_index(map, map->max_register) + 1;
+	cache = kzalloc_flex(*cache, data, cache_size, map->alloc_flags);
+	if (!cache)
+		return -ENOMEM;
+
+	cache->valid = bitmap_zalloc(cache_size, map->alloc_flags);
+	if (!cache->valid)
+		goto err_free;
+
+	map->cache = cache;
+
+	return 0;
+
+err_free:
+	kfree(cache);
+	return -ENOMEM;
+}
+
+static void regcache_flat_exit(struct regmap *map)
+{
+	struct regcache_flat_data *cache = map->cache;
+
+	if (cache)
+		bitmap_free(cache->valid);
+
+	kfree(cache);
+	map->cache = NULL;
+}
+
+static int regcache_flat_populate(struct regmap *map)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int i;
+
+	for (i = 0; i < map->num_reg_defaults; i++) {
+		unsigned int reg = map->reg_defaults[i].reg;
+		unsigned int index = regcache_flat_get_index(map, reg);
+
+		cache->data[index] = map->reg_defaults[i].def;
+		__set_bit(index, cache->valid);
+	}
+
+	if (map->reg_default_cb) {
+		dev_dbg(map->dev,
+			"Populating regcache_flat using reg_default_cb callback\n");
+
+		for (i = 0; i <= map->max_register; i += map->reg_stride) {
+			unsigned int index = regcache_flat_get_index(map, i);
+			unsigned int value;
+
+			if (test_bit(index, cache->valid))
+				continue;
+
+			if (map->reg_default_cb(map->dev, i, &value))
+				continue;
+
+			cache->data[index] = value;
+			__set_bit(index, cache->valid);
+		}
+	}
+
+	return 0;
+}
+
+static int regcache_flat_read(struct regmap *map,
+			      unsigned int reg, unsigned int *value)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int index = regcache_flat_get_index(map, reg);
+
+	/* legacy behavior: ignore validity, but warn the user */
+	if (unlikely(!test_bit(index, cache->valid)))
+		dev_warn_once(map->dev,
+			"using zero-initialized flat cache, this may cause unexpected behavior");
+
+	*value = cache->data[index];
+
+	return 0;
+}
+
+static int regcache_flat_sparse_read(struct regmap *map,
+				     unsigned int reg, unsigned int *value)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int index = regcache_flat_get_index(map, reg);
+
+	if (unlikely(!test_bit(index, cache->valid)))
+		return -ENOENT;
+
+	*value = cache->data[index];
+
+	return 0;
+}
+
+static int regcache_flat_write(struct regmap *map, unsigned int reg,
+			       unsigned int value)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int index = regcache_flat_get_index(map, reg);
+
+	cache->data[index] = value;
+	__set_bit(index, cache->valid);
+
+	return 0;
+}
+
+static int regcache_flat_drop(struct regmap *map, unsigned int min,
+			      unsigned int max)
+{
+	struct regcache_flat_data *cache = map->cache;
+	unsigned int bitmap_min = regcache_flat_get_index(map, min);
+	unsigned int bitmap_max = regcache_flat_get_index(map, max);
+
+	bitmap_clear(cache->valid, bitmap_min, bitmap_max + 1 - bitmap_min);
+
+	return 0;
+}
+
+struct regcache_ops regcache_flat_ops = {
+	.type = REGCACHE_FLAT,
+	.name = "flat",
+	.init = regcache_flat_init,
+	.exit = regcache_flat_exit,
+	.populate = regcache_flat_populate,
+	.read = regcache_flat_read,
+	.write = regcache_flat_write,
+};
+
+struct regcache_ops regcache_flat_sparse_ops = {
+	.type = REGCACHE_FLAT_S,
+	.name = "flat-sparse",
+	.init = regcache_flat_init,
+	.exit = regcache_flat_exit,
+	.populate = regcache_flat_populate,
+	.read = regcache_flat_sparse_read,
+	.write = regcache_flat_write,
+	.drop = regcache_flat_drop,
+};