The patch titled
Subject: lib/stackdepot.c: bump stackdepot capacity from 16MB to 128MB
has been removed from the -mm tree. Its filename was
lib-bump-stackdepot-capacity-from-16mb-to-128mb.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
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@xxxxxxxxxx
Signed-off-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Baozeng Ding <sploving1@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx are
kasan-support-panic_on_warn.patch
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