error-injection: Add injectable error types

Add injectable error types for each error-injectable function.

One motivation of error injection test is to find software flaws,
mistakes or mis-handlings of expectable errors. If we find such
flaws by the test, that is a program bug, so we need to fix it.

But if the tester miss input the error (e.g. just return success
code without processing anything), it causes unexpected behavior
even if the caller is correctly programmed to handle any errors.
That is not what we want to test by error injection.

To clarify what type of errors the caller must expect for each
injectable function, this introduces injectable error types:

 - EI_ETYPE_NULL : means the function will return NULL if it
		    fails. No ERR_PTR, just a NULL.
 - EI_ETYPE_ERRNO : means the function will return -ERRNO
		    if it fails.
 - EI_ETYPE_ERRNO_NULL : means the function will return -ERRNO
		       (ERR_PTR) or NULL.

ALLOW_ERROR_INJECTION() macro is expanded to get one of
NULL, ERRNO, ERRNO_NULL to record the error type for
each function. e.g.

 ALLOW_ERROR_INJECTION(open_ctree, ERRNO)

This error types are shown in debugfs as below.

  ====
  / # cat /sys/kernel/debug/error_injection/list
  open_ctree [btrfs]	ERRNO
  io_ctl_init [btrfs]	ERRNO
  ====
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

fs/btrfs/disk-io.c

@@ -3124,7 +3124,7 @@ int open_ctree(struct super_block *sb,
 		goto fail_block_groups;
 	goto retry_root_backup;
 }
-ALLOW_ERROR_INJECTION(open_ctree);
+ALLOW_ERROR_INJECTION(open_ctree, ERRNO);
 
 static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
 {

fs/btrfs/free-space-cache.c

@@ -333,7 +333,7 @@ static int io_ctl_init(struct btrfs_io_ctl *io_ctl, struct inode *inode,
 
 	return 0;
 }
-ALLOW_ERROR_INJECTION(io_ctl_init);
+ALLOW_ERROR_INJECTION(io_ctl_init, ERRNO);
 
 static void io_ctl_free(struct btrfs_io_ctl *io_ctl)
 {

include/asm-generic/error-injection.h

@@ -3,17 +3,32 @@
 #define _ASM_GENERIC_ERROR_INJECTION_H
 
 #if defined(__KERNEL__) && !defined(__ASSEMBLY__)
+enum {
+	EI_ETYPE_NONE,		/* Dummy value for undefined case */
+	EI_ETYPE_NULL,		/* Return NULL if failure */
+	EI_ETYPE_ERRNO,		/* Return -ERRNO if failure */
+	EI_ETYPE_ERRNO_NULL,	/* Return -ERRNO or NULL if failure */
+};
+
+struct error_injection_entry {
+	unsigned long	addr;
+	int		etype;
+};
+
 #ifdef CONFIG_FUNCTION_ERROR_INJECTION
 /*
  * Whitelist ganerating macro. Specify functions which can be
  * error-injectable using this macro.
  */
-#define ALLOW_ERROR_INJECTION(fname)					\
-static unsigned long __used						\
+#define ALLOW_ERROR_INJECTION(fname, _etype)				\
+static struct error_injection_entry __used				\
 	__attribute__((__section__("_error_injection_whitelist")))	\
-	_eil_addr_##fname = (unsigned long)fname;
+	_eil_addr_##fname = {						\
+		.addr = (unsigned long)fname,				\
+		.etype = EI_ETYPE_##_etype,				\
+	};
 #else
-#define ALLOW_ERROR_INJECTION(fname)
+#define ALLOW_ERROR_INJECTION(fname, _etype)
 #endif
 #endif
 

include/asm-generic/vmlinux.lds.h

@@ -137,7 +137,7 @@
 #endif
 
 #ifdef CONFIG_FUNCTION_ERROR_INJECTION
-#define ERROR_INJECT_WHITELIST()	. = ALIGN(8);			      \
+#define ERROR_INJECT_WHITELIST()	STRUCT_ALIGN();			      \
 			VMLINUX_SYMBOL(__start_error_injection_whitelist) = .;\
 			KEEP(*(_error_injection_whitelist))		      \
 			VMLINUX_SYMBOL(__stop_error_injection_whitelist) = .;

include/linux/error-injection.h

@@ -7,6 +7,7 @@
 #include <asm/error-injection.h>
 
 extern bool within_error_injection_list(unsigned long addr);
+extern int get_injectable_error_type(unsigned long addr);
 
 #else /* !CONFIG_FUNCTION_ERROR_INJECTION */
 
@@ -16,6 +17,11 @@ static inline bool within_error_injection_list(unsigned long addr)
 	return false;
 }
 
+static inline int get_injectable_error_type(unsigned long addr)
+{
+	return EI_ETYPE_NONE;
+}
+
 #endif
 
 #endif /* _LINUX_ERROR_INJECTION_H */

include/linux/module.h

@@ -19,6 +19,7 @@
 #include <linux/jump_label.h>
 #include <linux/export.h>
 #include <linux/rbtree_latch.h>
+#include <linux/error-injection.h>
 
 #include <linux/percpu.h>
 #include <asm/module.h>
@@ -477,8 +478,8 @@ struct module {
 #endif
 
 #ifdef CONFIG_FUNCTION_ERROR_INJECTION
+	struct error_injection_entry *ei_funcs;
 	unsigned int num_ei_funcs;
-	unsigned long *ei_funcs;
 #endif
 } ____cacheline_aligned __randomize_layout;
 #ifndef MODULE_ARCH_INIT

lib/error-inject.c

@@ -16,6 +16,7 @@ struct ei_entry {
 	struct list_head list;
 	unsigned long start_addr;
 	unsigned long end_addr;
+	int etype;
 	void *priv;
 };
 
@@ -35,6 +36,17 @@ bool within_error_injection_list(unsigned long addr)
 	return ret;
 }
 
+int get_injectable_error_type(unsigned long addr)
+{
+	struct ei_entry *ent;
+
+	list_for_each_entry(ent, &error_injection_list, list) {
+		if (addr >= ent->start_addr && addr < ent->end_addr)
+			return ent->etype;
+	}
+	return EI_ETYPE_NONE;
+}
+
 /*
  * Lookup and populate the error_injection_list.
  *
@@ -42,16 +54,17 @@ bool within_error_injection_list(unsigned long addr)
  * bpf_error_injection, so we need to populate the list of the symbols that have
  * been marked as safe for overriding.
  */
-static void populate_error_injection_list(unsigned long *start,
-					  unsigned long *end, void *priv)
+static void populate_error_injection_list(struct error_injection_entry *start,
+					  struct error_injection_entry *end,
+					  void *priv)
 {
-	unsigned long *iter;
+	struct error_injection_entry *iter;
 	struct ei_entry *ent;
 	unsigned long entry, offset = 0, size = 0;
 
 	mutex_lock(&ei_mutex);
 	for (iter = start; iter < end; iter++) {
-		entry = arch_deref_entry_point((void *)*iter);
+		entry = arch_deref_entry_point((void *)iter->addr);
 
 		if (!kernel_text_address(entry) ||
 		    !kallsyms_lookup_size_offset(entry, &size, &offset)) {
@@ -65,6 +78,7 @@ static void populate_error_injection_list(unsigned long *start,
 			break;
 		ent->start_addr = entry;
 		ent->end_addr = entry + size;
+		ent->etype = iter->etype;
 		ent->priv = priv;
 		INIT_LIST_HEAD(&ent->list);
 		list_add_tail(&ent->list, &error_injection_list);
@@ -73,8 +87,8 @@ static void populate_error_injection_list(unsigned long *start,
 }
 
 /* Markers of the _error_inject_whitelist section */
-extern unsigned long __start_error_injection_whitelist[];
-extern unsigned long __stop_error_injection_whitelist[];
+extern struct error_injection_entry __start_error_injection_whitelist[];
+extern struct error_injection_entry __stop_error_injection_whitelist[];
 
 static void __init populate_kernel_ei_list(void)
 {
@@ -157,11 +171,26 @@ static void *ei_seq_next(struct seq_file *m, void *v, loff_t *pos)
 	return seq_list_next(v, &error_injection_list, pos);
 }
 
+static const char *error_type_string(int etype)
+{
+	switch (etype) {
+	case EI_ETYPE_NULL:
+		return "NULL";
+	case EI_ETYPE_ERRNO:
+		return "ERRNO";
+	case EI_ETYPE_ERRNO_NULL:
+		return "ERRNO_NULL";
+	default:
+		return "(unknown)";
+	}
+}
+
 static int ei_seq_show(struct seq_file *m, void *v)
 {
 	struct ei_entry *ent = list_entry(v, struct ei_entry, list);
 
-	seq_printf(m, "%pf\n", (void *)ent->start_addr);
+	seq_printf(m, "%pf\t%s\n", (void *)ent->start_addr,
+		   error_type_string(ent->etype));
 	return 0;
 }