+ lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch added to -mm tree

+ lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch added to -mm tree

[akpm]

The patch titled
     Subject: lib/stackdepot.c: bump stackdepot capacity from 16MB to 128MB
has been added to the -mm tree.  Its filename is
     lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch

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------------------------------------------------------
From: Dmitry Vyukov <dvyukov@google.com>
Subject: 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@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Baozeng Ding <sploving1@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 lib/stackdepot.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN lib/stackdepot.c~lib-bump-stackdepot-capacity-from-16mb-to-128mb lib/stackdepot.c
--- a/lib/stackdepot.c~lib-bump-stackdepot-capacity-from-16mb-to-128mb
+++ a/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)
_

Patches currently in -mm which might be from dvyukov@google.com are

kasan-support-panic_on_warn.patch
lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch