[Devel] [PATCH RHEL7 COMMIT] lib/stackdepot.c: bump stackdepot capacity from 16MB to 128MB

[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 f28d718ba3f48966b65a11372a9eea4958c1bff8
Author: Dmitry Vyukov <dvyukov at google.com>
Date:   Fri Sep 15 17:27:31 2017 +0300

    lib/stackdepot.c: bump stackdepot capacity from 16MB to 128MB
    
    KASAN uses stackdepot to memorize stacks for all kmalloc/kfree calls.
    Current stackdepot capacity is 16MB (1024 top level entries x 4 pages on
    second level).  Size of each stack is (num_frames + 3) * sizeof(long).
    Which gives us ~84K stacks.  This capacity was chosen empirically and it
    is enough to run kernel normally.
    
    However, when lots of configs are enabled and a fuzzer tries to maximize
    code coverage, it easily hits the limit within tens of minutes.  I've
    tested for long a time with number of top level entries bumped 4x
    (4096).  And I think I've seen overflow only once.  But I don't have all
    configs enabled and code coverage has not reached maximum yet.  So bump
    it 8x to 8192.
    
    Since we have two-level table, memory cost of this is very moderate --
    currently the top-level table is 8KB, with this patch it is 64KB, which
    is negligible under KASAN.
    
    Here is some approx math.
    
    128MB allows us to memorize ~670K stacks (assuming stack is ~200b).
    I've grepped kernel for kmalloc|kfree|kmem_cache_alloc|kmem_cache_free|
    kzalloc|kstrdup|kstrndup|kmemdup and it gives ~60K matches.  Most of
    alloc/free call sites are reachable with only one stack.  But some
    utility functions can have large fanout.  Assuming average fanout is 5x,
    total number of alloc/free stacks is ~300K.
    
    Link: http://lkml.kernel.org/r/1476458416-122131-1-git-send-email-dvyukov@google.com
    Signed-off-by: Dmitry Vyukov <dvyukov at google.com>
    Cc: Andrey Ryabinin <aryabinin at virtuozzo.com>
    Cc: Alexander Potapenko <glider at google.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim at lge.com>
    Cc: Baozeng Ding <sploving1 at gmail.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 02754e0a484a50a92d44c38879f2cb2792ebc572)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 lib/stackdepot.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 60f77f1..4d830e2 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -50,7 +50,7 @@
 					STACK_ALLOC_ALIGN)
 #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_SLABS_CAP 8192
 #define STACK_ALLOC_MAX_SLABS \
 	(((1LL << (STACK_ALLOC_INDEX_BITS)) < STACK_ALLOC_SLABS_CAP) ? \
 	 (1LL << (STACK_ALLOC_INDEX_BITS)) : STACK_ALLOC_SLABS_CAP)