[Devel] [PATCH RHEL7 COMMIT] lib/stackdepot: avoid to return 0 handle

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-693.1.1.vz7.37.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-693.1.1.vz7.37.4
------>
commit 029207c16cf35594a95725fb183d19694c761e34
Author: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Date:   Fri Sep 15 17:18:04 2017 +0300

    lib/stackdepot: avoid to return 0 handle
    
    Recently, we allow to save the stacktrace whose hashed value is 0.  It
    causes the problem that stackdepot could return 0 even if in success.
    User of stackdepot cannot distinguish whether it is success or not so we
    need to solve this problem.  In this patch, 1 bit are added to handle
    and make valid handle none 0 by setting this bit.  After that, valid
    handle will not be 0 and 0 handle will represent failure correctly.
    
    Fixes: 33334e25769c ("lib/stackdepot.c: allow the stack trace hash to be zero")
    Link: http://lkml.kernel.org/r/1462252403-1106-1-git-send-email-iamjoonsoo.kim@lge.com
    Signed-off-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
    Cc: Alexander Potapenko <glider at google.com>
    Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    
    https://jira.sw.ru/browse/PSBM-69081
    (cherry picked from commit 7c31190bcfdbff225950902a9f226e4eb79ca94f)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 lib/stackdepot.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 9e0b031..53ad6c0 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -42,12 +42,14 @@
 
 #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
 
+#define STACK_ALLOC_NULL_PROTECTION_BITS 1
 #define STACK_ALLOC_ORDER 2 /* 'Slab' size order for stack depot, 4 pages */
 #define STACK_ALLOC_SIZE (1LL << (PAGE_SHIFT + STACK_ALLOC_ORDER))
 #define STACK_ALLOC_ALIGN 4
 #define STACK_ALLOC_OFFSET_BITS (STACK_ALLOC_ORDER + PAGE_SHIFT - \
 					STACK_ALLOC_ALIGN)
-#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - STACK_ALLOC_OFFSET_BITS)
+#define STACK_ALLOC_INDEX_BITS (DEPOT_STACK_BITS - \
+		STACK_ALLOC_NULL_PROTECTION_BITS - STACK_ALLOC_OFFSET_BITS)
 #define STACK_ALLOC_SLABS_CAP 1024
 #define STACK_ALLOC_MAX_SLABS \
 	(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
@@ -59,6 +61,7 @@ union handle_parts {
 	struct {
 		u32 slabindex : STACK_ALLOC_INDEX_BITS;
 		u32 offset : STACK_ALLOC_OFFSET_BITS;
+		u32 valid : STACK_ALLOC_NULL_PROTECTION_BITS;
 	};
 };
 
@@ -136,6 +139,7 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
 	stack->size = size;
 	stack->handle.slabindex = depot_index;
 	stack->handle.offset = depot_offset >> STACK_ALLOC_ALIGN;
+	stack->handle.valid = 1;
 	memcpy(stack->entries, entries, size * sizeof(unsigned long));
 	depot_offset += required_size;