debugfs: fix error when writing negative value to atomic_t debugfs file

The simple attribute files do not accept a negative value since the commit
488dac0c9237 ("libfs: fix error cast of negative value in
simple_attr_write()"), so we have to use a 64-bit value to write a
negative value for a debugfs file created by debugfs_create_atomic_t().

This restores the previous behaviour by introducing
DEFINE_DEBUGFS_ATTRIBUTE_SIGNED for a signed value.

Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 488dac0c9237 ("libfs: fix error cast of negative value in simple_attr_write()")
Signed-off-by: Akinobu Mita <[e-mail]>
Reported-by: Zhao Gongyi <[e-mail]>
Reviewed-by: David Hildenbrand <[e-mail]>
Reviewed-by: Greg Kroah-Hartman <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Oscar Salvador <[e-mail]>
Cc: Rafael J. Wysocki <[e-mail]>
Cc: Shuah Khan <[e-mail]>
Cc: Wei Yongjun <[e-mail]>
Cc: Yicong Yang <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

Documentation/fault-injection/fault-injection.rst

···
 - /sys/kernel/debug/fail*/times:
 
 	specifies how many times failures may happen at most. A value of -1
-	means "no limit". Note, though, that this file only accepts unsigned
-	values. So, if you want to specify -1, you better use 'printf' instead
-	of 'echo', e.g.: $ printf %#x -1 > times
+	means "no limit".
 
 - /sys/kernel/debug/fail*/space:
 
···
     echo Y > /sys/kernel/debug/$FAILTYPE/task-filter
     echo 10 > /sys/kernel/debug/$FAILTYPE/probability
     echo 100 > /sys/kernel/debug/$FAILTYPE/interval
-    printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
+    echo -1 > /sys/kernel/debug/$FAILTYPE/times
     echo 0 > /sys/kernel/debug/$FAILTYPE/space
     echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
     echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
···
     echo N > /sys/kernel/debug/$FAILTYPE/task-filter
     echo 10 > /sys/kernel/debug/$FAILTYPE/probability
     echo 100 > /sys/kernel/debug/$FAILTYPE/interval
-    printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
+    echo -1 > /sys/kernel/debug/$FAILTYPE/times
     echo 0 > /sys/kernel/debug/$FAILTYPE/space
     echo 2 > /sys/kernel/debug/$FAILTYPE/verbose
     echo Y > /sys/kernel/debug/$FAILTYPE/ignore-gfp-wait
···
     echo N > /sys/kernel/debug/$FAILTYPE/task-filter
     echo 100 > /sys/kernel/debug/$FAILTYPE/probability
     echo 0 > /sys/kernel/debug/$FAILTYPE/interval
-    printf %#x -1 > /sys/kernel/debug/$FAILTYPE/times
+    echo -1 > /sys/kernel/debug/$FAILTYPE/times
     echo 0 > /sys/kernel/debug/$FAILTYPE/space
     echo 1 > /sys/kernel/debug/$FAILTYPE/verbose
 

fs/debugfs/file.c

···
 }
 EXPORT_SYMBOL_GPL(debugfs_attr_read);
 
-ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
-			 size_t len, loff_t *ppos)
+static ssize_t debugfs_attr_write_xsigned(struct file *file, const char __user *buf,
+			 size_t len, loff_t *ppos, bool is_signed)
 {
 	struct dentry *dentry = F_DENTRY(file);
 	ssize_t ret;
···
 	ret = debugfs_file_get(dentry);
 	if (unlikely(ret))
 		return ret;
-	ret = simple_attr_write(file, buf, len, ppos);
+	if (is_signed)
+		ret = simple_attr_write_signed(file, buf, len, ppos);
+	else
+		ret = simple_attr_write(file, buf, len, ppos);
 	debugfs_file_put(dentry);
 	return ret;
 }
+
+ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
+			 size_t len, loff_t *ppos)
+{
+	return debugfs_attr_write_xsigned(file, buf, len, ppos, false);
+}
 EXPORT_SYMBOL_GPL(debugfs_attr_write);
+
+ssize_t debugfs_attr_write_signed(struct file *file, const char __user *buf,
+			 size_t len, loff_t *ppos)
+{
+	return debugfs_attr_write_xsigned(file, buf, len, ppos, true);
+}
+EXPORT_SYMBOL_GPL(debugfs_attr_write_signed);
 
 static struct dentry *debugfs_create_mode_unsafe(const char *name, umode_t mode,
 					struct dentry *parent, void *value,
···
 	*val = atomic_read((atomic_t *)data);
 	return 0;
 }
-DEFINE_DEBUGFS_ATTRIBUTE(fops_atomic_t, debugfs_atomic_t_get,
+DEFINE_DEBUGFS_ATTRIBUTE_SIGNED(fops_atomic_t, debugfs_atomic_t_get,
 			debugfs_atomic_t_set, "%lld\n");
-DEFINE_DEBUGFS_ATTRIBUTE(fops_atomic_t_ro, debugfs_atomic_t_get, NULL,
+DEFINE_DEBUGFS_ATTRIBUTE_SIGNED(fops_atomic_t_ro, debugfs_atomic_t_get, NULL,
 			"%lld\n");
-DEFINE_DEBUGFS_ATTRIBUTE(fops_atomic_t_wo, NULL, debugfs_atomic_t_set,
+DEFINE_DEBUGFS_ATTRIBUTE_SIGNED(fops_atomic_t_wo, NULL, debugfs_atomic_t_set,
 			"%lld\n");
 
 /**

include/linux/debugfs.h

···
 
 extern struct dentry *arch_debugfs_dir;
 
-#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\
+#define DEFINE_DEBUGFS_ATTRIBUTE_XSIGNED(__fops, __get, __set, __fmt, __is_signed)	\
 static int __fops ## _open(struct inode *inode, struct file *file)	\
 {									\
 	__simple_attr_check_format(__fmt, 0ull);			\
···
 	.open	 = __fops ## _open,					\
 	.release = simple_attr_release,					\
 	.read	 = debugfs_attr_read,					\
-	.write	 = debugfs_attr_write,					\
+	.write	 = (__is_signed) ? debugfs_attr_write_signed : debugfs_attr_write,	\
 	.llseek  = no_llseek,						\
 }
+
+#define DEFINE_DEBUGFS_ATTRIBUTE(__fops, __get, __set, __fmt)		\
+	DEFINE_DEBUGFS_ATTRIBUTE_XSIGNED(__fops, __get, __set, __fmt, false)
+
+#define DEFINE_DEBUGFS_ATTRIBUTE_SIGNED(__fops, __get, __set, __fmt)	\
+	DEFINE_DEBUGFS_ATTRIBUTE_XSIGNED(__fops, __get, __set, __fmt, true)
 
 typedef struct vfsmount *(*debugfs_automount_t)(struct dentry *, void *);
 
···
 ssize_t debugfs_attr_read(struct file *file, char __user *buf,
 			size_t len, loff_t *ppos);
 ssize_t debugfs_attr_write(struct file *file, const char __user *buf,
+			size_t len, loff_t *ppos);
+ssize_t debugfs_attr_write_signed(struct file *file, const char __user *buf,
 			size_t len, loff_t *ppos);
 
 struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
···
 }
 
 static inline ssize_t debugfs_attr_write(struct file *file,
+					const char __user *buf,
+					size_t len, loff_t *ppos)
+{
+	return -ENODEV;
+}
+
+static inline ssize_t debugfs_attr_write_signed(struct file *file,
 					const char __user *buf,
 					size_t len, loff_t *ppos)
 {