WARN_ON out of range error in ERR_PTR?

[Benny Halevy <bhalevy@panasas.com>]

Andrew,

After hitting a bug where an nfs error -10021 wasn't handled
correctly since IS_ERR returned false on its ERR_PTR value
I realized that adding a BUG_ON to make sure the mapped error
is in the valid range would have caught this.

Since ERR_PTR is not called on the critical path
(unlike IS_ERR) but rather on the error handling path I believe
we can tolerate the extra cost.

The reason this is just a WARN_ON and not BUG_ON is to make
fixing it easier, although I do consider calling ERR_PTR on an
out of range error a pretty dangerous bug as the error might go
unnoticed.

How about committing the following patch to -mm?

Signed-off-by: Benny Halevy <bhalevy@panasas.com>
---
 include/linux/err.h |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/include/linux/err.h b/include/linux/err.h
index ec87f31..81df84f 100644
--- a/include/linux/err.h
+++ b/include/linux/err.h
@@ -2,7 +2,7 @@
 #define _LINUX_ERR_H
 
 #include <linux/compiler.h>
-
+#include <asm/bug.h>
 #include <asm/errno.h>
 
 /*
@@ -21,6 +21,7 @@
 
 static inline void *ERR_PTR(long error)
 {
+	WARN_ON(error && !IS_ERR_VALUE(error));
 	return (void *) error;
 }
 
-- 
1.6.0.2