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, 97 insertions, 0 deletions

diff --git a/include/kunit/test-bug.h b/include/kunit/test-bug.h
new file mode 100644
index 000000000..99869029f
--- /dev/null
+++ b/include/kunit/test-bug.h
@@ -0,0 +1,97 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit API providing hooks for non-test code to interact with tests.
+ *
+ * Copyright (C) 2020, Google LLC.
+ * Author: Uriel Guajardo <urielguajardo@google.com>
+ */
+
+#ifndef _KUNIT_TEST_BUG_H
+#define _KUNIT_TEST_BUG_H
+
+#include <linux/stddef.h> /* for NULL */
+#include <linux/types.h>  /* for bool */
+
+#if IS_ENABLED(CONFIG_KUNIT)
+
+#include <linux/jump_label.h> /* For static branch */
+#include <linux/sched.h>
+
+/* Static key if KUnit is running any tests. */
+DECLARE_STATIC_KEY_FALSE(kunit_running);
+
+/* Hooks table: a table of function pointers filled in when kunit loads */
+extern struct kunit_hooks_table {
+	__printf(3, 4) void (*fail_current_test)(const char*, int, const char*, ...);
+	void *(*get_static_stub_address)(struct kunit *test, void *real_fn_addr);
+	bool (*is_suppressed_warning)(bool count);
+} kunit_hooks;
+
+/**
+ * kunit_get_current_test() - Return a pointer to the currently running
+ *			      KUnit test.
+ *
+ * If a KUnit test is running in the current task, returns a pointer to its
+ * associated struct kunit. This pointer can then be passed to any KUnit
+ * function or assertion. If no test is running (or a test is running in a
+ * different task), returns NULL.
+ *
+ * This function is safe to call even when KUnit is disabled. If CONFIG_KUNIT
+ * is not enabled, it will compile down to nothing and will return quickly no
+ * test is running.
+ */
+static inline struct kunit *kunit_get_current_test(void)
+{
+	if (!static_branch_unlikely(&kunit_running))
+		return NULL;
+
+	return current->kunit_test;
+}
+
+
+/**
+ * kunit_fail_current_test() - If a KUnit test is running, fail it.
+ *
+ * If a KUnit test is running in the current task, mark that test as failed.
+ */
+#define kunit_fail_current_test(fmt, ...) do {					\
+		if (static_branch_unlikely(&kunit_running)) {			\
+			/* Guaranteed to be non-NULL when kunit_running true*/	\
+			kunit_hooks.fail_current_test(__FILE__, __LINE__,	\
+						  fmt, ##__VA_ARGS__);		\
+		}								\
+	} while (0)
+
+/**
+ * kunit_is_suppressed_warning() - Check if warnings are being suppressed
+ *                                 by the current KUnit test.
+ * @count: if true, increment the suppression counter on match.
+ *
+ * Returns true if the current task has active warning suppression.
+ * Uses the kunit_running static branch for zero overhead when no tests run.
+ *
+ * A single WARN*() may traverse multiple call sites in the warning path
+ * (e.g., __warn_printk() and __report_bug()). Pass @count = true at the
+ * primary suppression point to count each warning exactly once, and
+ * @count = false at secondary points to suppress output without
+ * inflating the count.
+ */
+static inline bool kunit_is_suppressed_warning(bool count)
+{
+	if (!static_branch_unlikely(&kunit_running))
+		return false;
+
+	return kunit_hooks.is_suppressed_warning &&
+	       kunit_hooks.is_suppressed_warning(count);
+}
+
+#else
+
+static inline struct kunit *kunit_get_current_test(void) { return NULL; }
+static inline bool kunit_is_suppressed_warning(bool count) { return false; }
+
+#define kunit_fail_current_test(fmt, ...) do {} while (0)
+
+#endif
+
+#endif /* _KUNIT_TEST_BUG_H */