[lkml]   [2022]   [Dec]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
Patch in this message
Subject[PATCH 2/2] docs: fault-injection: Add requirements of error injectable functions
From: Masami Hiramatsu (Google) <>

Add a section about the requirements of the error injectable functions
and the type of errors.
Since this section must be read before using ALLOW_ERROR_INJECTION()
macro, that section is referred from the comment of the macro too.

Signed-off-by: Masami Hiramatsu (Google) <>
Documentation/fault-injection/fault-injection.rst | 65 +++++++++++++++++++++
include/asm-generic/error-injection.h | 6 +-
2 files changed, 69 insertions(+), 2 deletions(-)

diff --git a/Documentation/fault-injection/fault-injection.rst b/Documentation/fault-injection/fault-injection.rst
index 17779a2772e5..da6c5796b1f8 100644
--- a/Documentation/fault-injection/fault-injection.rst
+++ b/Documentation/fault-injection/fault-injection.rst
@@ -233,6 +233,71 @@ proc entries
This feature is intended for systematic testing of faults in a single
system call. See an example below.

+Error Injectable Functions
+This part is for the kenrel developers considering to add a function to
+Requirements for the Error Injectable Functions
+Since the function-level error injection forcibly changes the code path
+and returns an error even if the input and conditions are proper, this can
+cause unexpected kernel crash if you allow error injection on the function
+which is NOT error injectable. Thus, you (and reviewers) must ensure;
+- The function returns an error code if it fails, and the callers must check
+ it correctly (need to recover from it).
+- The function does not execute any code which can change any state before
+ the first error return. The state includes global or local, or input
+ variable. For example, clear output address storage (e.g. `*ret = NULL`),
+ increments/decrements counter, set a flag, preempt/irq disable or get
+ a lock (if those are recovered before returning error, that will be OK.)
+The first requirement is important, and it will result in that the release
+(free objects) functions are usually harder to inject errors than allocate
+functions. If errors of such release functions are not correctly handled
+it will cause a memory leak easily (the caller will confuse that the object
+has been released or corrupted.)
+The second one is for the caller which expects the function should always
+does something. Thus if the function error injection skips whole of the
+function, the expectation is betrayed and causes an unexpected error.
+Type of the Error Injectable Functions
+Each error injectable functions will have the error type specified by the
+ALLOW_ERROR_INJECTION() macro. You have to choose it carefully if you add
+a new error injectable function. If the wrong error type is chosen, the
+kernel may crash because it may not be able to handle the error.
+There are 4 types of errors defined in include/asm-generic/error-injection.h
+ This function will return `NULL` if it fails. e.g. return an allocateed
+ object address.
+ This function will return an `-errno` error code if it fails. e.g. return
+ -EINVAL if the input is wrong. This will include the functions which will
+ return an address which encodes `-errno` by ERR_PTR() macro.
+ This function will return an `-errno` or `NULL` if it fails. If the caller
+ of this function checks the return value with IS_ERR_OR_NULL() macro, this
+ type will be appropriate.
+ This function will return `true` (non-zero positive value) if it fails.
+If you specifies a wrong type, for example, EI_TYPE_ERRNO for the function
+which returns an allocated object, it may cause a problem because the returned
+value is not an object address and the caller can not access to the address.
How to add new fault injection capability

diff --git a/include/asm-generic/error-injection.h b/include/asm-generic/error-injection.h
index c0b9d3217ed9..b05253f68eaa 100644
--- a/include/asm-generic/error-injection.h
+++ b/include/asm-generic/error-injection.h
@@ -19,8 +19,10 @@ struct pt_regs;

- * Whitelist generating macro. Specify functions which can be
- * error-injectable using this macro.
+ * Whitelist generating macro. Specify functions which can be error-injectable
+ * using this macro. If you unsure what is required for the error-injectable
+ * functions, please read Documentation/fault-injection/fault-injection.rst
+ * 'Error Injectable Functions' section.
#define ALLOW_ERROR_INJECTION(fname, _etype) \
static struct error_injection_entry __used \
 \ /
  Last update: 2022-12-12 03:47    [W:0.092 / U:0.432 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site