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, 139 insertions, 0 deletions

diff --git a/lib/test_bitops.c b/lib/test_bitops.c
new file mode 100644
index 000000000..55669624b
--- /dev/null
+++ b/lib/test_bitops.c
@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2020 Intel Corporation
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/cleanup.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/slab.h>
+
+/* a tiny module only meant to test
+ *
+ *   set/clear_bit
+ *   get_count_order/long
+ */
+
+/* use an enum because that's the most common BITMAP usage */
+enum bitops_fun {
+	BITOPS_4 = 4,
+	BITOPS_7 = 7,
+	BITOPS_11 = 11,
+	BITOPS_31 = 31,
+	BITOPS_88 = 88,
+	BITOPS_LAST = 255,
+	BITOPS_LENGTH = 256
+};
+
+static DECLARE_BITMAP(g_bitmap, BITOPS_LENGTH);
+
+static unsigned int order_comb[][2] = {
+	{0x00000003,  2},
+	{0x00000004,  2},
+	{0x00001fff, 13},
+	{0x00002000, 13},
+	{0x50000000, 31},
+	{0x80000000, 31},
+	{0x80003000, 32},
+};
+
+#ifdef CONFIG_64BIT
+static unsigned long order_comb_long[][2] = {
+	{0x0000000300000000, 34},
+	{0x0000000400000000, 34},
+	{0x00001fff00000000, 45},
+	{0x0000200000000000, 45},
+	{0x5000000000000000, 63},
+	{0x8000000000000000, 63},
+	{0x8000300000000000, 64},
+};
+#endif
+
+static int __init test_fns(void)
+{
+	static volatile __always_used unsigned long tmp __initdata;
+	unsigned long *buf __free(kfree) = NULL;
+	unsigned int i, n;
+	ktime_t time;
+
+	buf = kmalloc_array(10000, sizeof(unsigned long), GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	get_random_bytes(buf, 10000 * sizeof(unsigned long));
+	time = ktime_get();
+
+	for (n = 0; n < BITS_PER_LONG; n++)
+		for (i = 0; i < 10000; i++)
+			tmp = fns(buf[i], n);
+
+	time = ktime_get() - time;
+	pr_err("fns:  %18llu ns\n", time);
+
+	return 0;
+}
+
+static int __init test_bitops_startup(void)
+{
+	int i, bit_set;
+
+	pr_info("Starting bitops test\n");
+	set_bit(BITOPS_4, g_bitmap);
+	set_bit(BITOPS_7, g_bitmap);
+	set_bit(BITOPS_11, g_bitmap);
+	set_bit(BITOPS_31, g_bitmap);
+	set_bit(BITOPS_88, g_bitmap);
+
+	for (i = 0; i < ARRAY_SIZE(order_comb); i++) {
+		if (order_comb[i][1] != get_count_order(order_comb[i][0]))
+			pr_warn("get_count_order wrong for %x\n",
+				       order_comb[i][0]);
+	}
+
+	for (i = 0; i < ARRAY_SIZE(order_comb); i++) {
+		if (order_comb[i][1] != get_count_order_long(order_comb[i][0]))
+			pr_warn("get_count_order_long wrong for %x\n",
+				       order_comb[i][0]);
+	}
+
+#ifdef CONFIG_64BIT
+	for (i = 0; i < ARRAY_SIZE(order_comb_long); i++) {
+		if (order_comb_long[i][1] !=
+			       get_count_order_long(order_comb_long[i][0]))
+			pr_warn("get_count_order_long wrong for %lx\n",
+				       order_comb_long[i][0]);
+	}
+#endif
+
+	barrier();
+
+	clear_bit(BITOPS_4, g_bitmap);
+	clear_bit(BITOPS_7, g_bitmap);
+	clear_bit(BITOPS_11, g_bitmap);
+	clear_bit(BITOPS_31, g_bitmap);
+	clear_bit(BITOPS_88, g_bitmap);
+
+	bit_set = find_first_bit(g_bitmap, BITOPS_LAST);
+	if (bit_set != BITOPS_LAST)
+		pr_err("ERROR: FOUND SET BIT %d\n", bit_set);
+
+	test_fns();
+
+	pr_info("Completed bitops test\n");
+
+	return 0;
+}
+
+static void __exit test_bitops_unstartup(void)
+{
+}
+
+module_init(test_bitops_startup);
+module_exit(test_bitops_unstartup);
+
+MODULE_AUTHOR("Jesse Brandeburg <jesse.brandeburg@intel.com>, Wei Yang <richard.weiyang@gmail.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Bit testing module");