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, 90 insertions, 0 deletions

diff --git a/drivers/acpi/hed.c b/drivers/acpi/hed.c
new file mode 100644
index 000000000..48562f53d
--- /dev/null
+++ b/drivers/acpi/hed.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ACPI Hardware Error Device (PNP0C33) Driver
+ *
+ * Copyright (C) 2010, Intel Corp.
+ *	Author: Huang Ying <ying.huang@intel.com>
+ *
+ * ACPI Hardware Error Device is used to report some hardware errors
+ * notified via SCI, mainly the corrected errors.
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/acpi.h>
+#include <linux/platform_device.h>
+#include <acpi/hed.h>
+
+static const struct acpi_device_id acpi_hed_ids[] = {
+	{"PNP0C33", 0},
+	{"", 0},
+};
+MODULE_DEVICE_TABLE(acpi, acpi_hed_ids);
+
+static bool hed_present;
+
+static BLOCKING_NOTIFIER_HEAD(acpi_hed_notify_list);
+
+int register_acpi_hed_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&acpi_hed_notify_list, nb);
+}
+EXPORT_SYMBOL_GPL(register_acpi_hed_notifier);
+
+void unregister_acpi_hed_notifier(struct notifier_block *nb)
+{
+	blocking_notifier_chain_unregister(&acpi_hed_notify_list, nb);
+}
+EXPORT_SYMBOL_GPL(unregister_acpi_hed_notifier);
+
+/*
+ * SCI to report hardware error is forwarded to the listeners of HED,
+ * it is used by HEST Generic Hardware Error Source with notify type
+ * SCI.
+ */
+static void acpi_hed_notify(acpi_handle handle, u32 event, void *data)
+{
+	blocking_notifier_call_chain(&acpi_hed_notify_list, 0, NULL);
+}
+
+static int acpi_hed_probe(struct platform_device *pdev)
+{
+	int err;
+
+	/* Only one hardware error device */
+	if (hed_present)
+		return -EINVAL;
+
+	err = devm_acpi_install_notify_handler(&pdev->dev, ACPI_DEVICE_NOTIFY,
+					       acpi_hed_notify, NULL);
+	if (err)
+		return err;
+
+	hed_present = true;
+	return 0;
+}
+
+static void acpi_hed_remove(struct platform_device *pdev)
+{
+	hed_present = false;
+}
+
+static struct platform_driver acpi_hed_driver = {
+	.probe = acpi_hed_probe,
+	.remove = acpi_hed_remove,
+	.driver = {
+		.name = "acpi-hardware-error-device",
+		.acpi_match_table = acpi_hed_ids,
+	},
+};
+
+static int __init acpi_hed_driver_init(void)
+{
+	return platform_driver_register(&acpi_hed_driver);
+}
+subsys_initcall(acpi_hed_driver_init);
+
+MODULE_AUTHOR("Huang Ying");
+MODULE_DESCRIPTION("ACPI Hardware Error Device Driver");
+MODULE_LICENSE("GPL");