On Thu, Nov 17, 2016 at 09:40:20AM -0800, Linus Torvalds wrote:
> On Thu, Nov 17, 2016 at 9:25 AM, Luc Van Oostenryck
> <luc.vanoostenryck@xxxxxxxxx> wrote:
> > The macros that do the ptrlist walking don't handle empty blocks.
>
> Actually, most of the_do_ handle empty blocks. In particular, the
> normal FOR_EACH_PTR() case should handle it just fine.
Yes, indeed.
> The exception is, I think:
>
> - first_ptr_list/last_ptr_list
>
> - DO_PREPARE/DO_RESET
...
> I suspect they should be fairly easy to update to just walk the list
> until they hit a non-empty case (like DO_NEXT() already does, for
> example).
>
> Linus
> --
Would something like the following be fine?
>From bf7f856f95a71b931559a17c0f5144cd3a3875b5 Mon Sep 17 00:00:00 2001
From: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
Date: Thu, 17 Nov 2016 20:59:18 +0100
Subject: [PATCH] make ptrlist walking against robust against empty blocks
Not all macros or function involved in the ptrlist walking
can handle a ptrlist containing some empty blocks.
Fix this by:
- add the proper check & looping to first & last_ptr_list().
- add a safe version of PTR_ENTRY doing the needed check & looping.
- use this safe version for DO_PREPARE() & DO_RESET()
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
I've quickly checked it on the testsuite (and it seems to pass ;).
I'll validate this more thoroughly but I won't be able to do this
just now.
---
ptrlist.h | 29 ++++++++++++++++++++++++++---
1 file changed, 26 insertions(+), 3 deletions(-)
diff --git a/ptrlist.h b/ptrlist.h
index 61e159fd..d09be2f5 100644
--- a/ptrlist.h
+++ b/ptrlist.h
@@ -67,28 +67,51 @@ extern int linearize_ptr_list(struct ptr_list *, void **, int);
static inline void *first_ptr_list(struct ptr_list *list)
{
+ struct ptr_list *head = list;
+
if (!list)
return NULL;
+
+ while (list->nr == 0) {
+ list = list->next;
+ if (list == head)
+ return NULL;
+ }
return PTR_ENTRY(list, 0);
}
static inline void *last_ptr_list(struct ptr_list *list)
{
+ struct ptr_list *head = list;
if (!list)
return NULL;
list = list->prev;
+ while (list->nr == 0) {
+ if (list == head)
+ return NULL;
+ list = list->prev;
+ }
return PTR_ENTRY(list, list->nr-1);
}
+#define PTR_DEREF(__head, idx, PTR_ENTRY) ({ \
+ struct ptr_list *__list = __head; \
+ while (__list && __list->nr == 0) { \
+ __list = __list->next; \
+ if (__list == __head) \
+ __list = NULL; \
+ } \
+ __list ? PTR_ENTRY(__list, idx) : NULL; \
+})
+
#define DO_PREPARE(head, ptr, __head, __list, __nr, PTR_ENTRY) \
do { \
struct ptr_list *__head = (struct ptr_list *) (head); \
struct ptr_list *__list = __head; \
int __nr = 0; \
CHECK_TYPE(head,ptr); \
- if (__head) ptr = PTR_ENTRY(__head, 0); \
- else ptr = NULL
+ ptr = PTR_DEREF(__head, 0, PTR_ENTRY); \
#define DO_NEXT(ptr, __head, __list, __nr, PTR_ENTRY) \
if (ptr) { \
@@ -110,7 +133,7 @@ static inline void *last_ptr_list(struct ptr_list *list)
do { \
__nr = 0; \
__list = __head; \
- if (__head) ptr = PTR_ENTRY(__head, 0); \
+ if (__head) ptr = PTR_DEREF(__head, 0, PTR_ENTRY); \
} while (0)
#define DO_FINISH(ptr, __head, __list, __nr) \
--
2.10.2
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