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Subject[PATCH 4.9 20/91] mm/slab.c: kmemleak no scan alien caches
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 92d1d07daad65c300c7d0b68bbef8867e9895d54 ]

Kmemleak throws endless warnings during boot due to in
__alloc_alien_cache(),

alc = kmalloc_node(memsize, gfp, node);
init_arraycache(&alc->ac, entries, batch);
kmemleak_no_scan(ac);

Kmemleak does not track the array cache (alc->ac) but the alien cache
(alc) instead, so let it track the latter by lifting kmemleak_no_scan()
out of init_arraycache().

There is another place that calls init_arraycache(), but
alloc_kmem_cache_cpus() uses the percpu allocation where will never be
considered as a leak.

kmemleak: Found object by alias at 0xffff8007b9aa7e38
CPU: 190 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc2+ #2
Call trace:
dump_backtrace+0x0/0x168
show_stack+0x24/0x30
dump_stack+0x88/0xb0
lookup_object+0x84/0xac
find_and_get_object+0x84/0xe4
kmemleak_no_scan+0x74/0xf4
setup_kmem_cache_node+0x2b4/0x35c
__do_tune_cpucache+0x250/0x2d4
do_tune_cpucache+0x4c/0xe4
enable_cpucache+0xc8/0x110
setup_cpu_cache+0x40/0x1b8
__kmem_cache_create+0x240/0x358
create_cache+0xc0/0x198
kmem_cache_create_usercopy+0x158/0x20c
kmem_cache_create+0x50/0x64
fsnotify_init+0x58/0x6c
do_one_initcall+0x194/0x388
kernel_init_freeable+0x668/0x688
kernel_init+0x18/0x124
ret_from_fork+0x10/0x18
kmemleak: Object 0xffff8007b9aa7e00 (size 256):
kmemleak: comm "swapper/0", pid 1, jiffies 4294697137
kmemleak: min_count = 1
kmemleak: count = 0
kmemleak: flags = 0x1
kmemleak: checksum = 0
kmemleak: backtrace:
kmemleak_alloc+0x84/0xb8
kmem_cache_alloc_node_trace+0x31c/0x3a0
__kmalloc_node+0x58/0x78
setup_kmem_cache_node+0x26c/0x35c
__do_tune_cpucache+0x250/0x2d4
do_tune_cpucache+0x4c/0xe4
enable_cpucache+0xc8/0x110
setup_cpu_cache+0x40/0x1b8
__kmem_cache_create+0x240/0x358
create_cache+0xc0/0x198
kmem_cache_create_usercopy+0x158/0x20c
kmem_cache_create+0x50/0x64
fsnotify_init+0x58/0x6c
do_one_initcall+0x194/0x388
kernel_init_freeable+0x668/0x688
kernel_init+0x18/0x124
kmemleak: Not scanning unknown object at 0xffff8007b9aa7e38
CPU: 190 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc2+ #2
Call trace:
dump_backtrace+0x0/0x168
show_stack+0x24/0x30
dump_stack+0x88/0xb0
kmemleak_no_scan+0x90/0xf4
setup_kmem_cache_node+0x2b4/0x35c
__do_tune_cpucache+0x250/0x2d4
do_tune_cpucache+0x4c/0xe4
enable_cpucache+0xc8/0x110
setup_cpu_cache+0x40/0x1b8
__kmem_cache_create+0x240/0x358
create_cache+0xc0/0x198
kmem_cache_create_usercopy+0x158/0x20c
kmem_cache_create+0x50/0x64
fsnotify_init+0x58/0x6c
do_one_initcall+0x194/0x388
kernel_init_freeable+0x668/0x688
kernel_init+0x18/0x124
ret_from_fork+0x10/0x18

Link: http://lkml.kernel.org/r/20190129184518.39808-1-cai@lca.pw
Fixes: 1fe00d50a9e8 ("slab: factor out initialization of array cache")
Signed-off-by: Qian Cai <cai@lca.pw>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
mm/slab.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/mm/slab.c b/mm/slab.c
index 354a09deecff..d2c0499c6b15 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -566,14 +566,6 @@ static void start_cpu_timer(int cpu)

static void init_arraycache(struct array_cache *ac, int limit, int batch)
{
- /*
- * The array_cache structures contain pointers to free object.
- * However, when such objects are allocated or transferred to another
- * cache the pointers are not cleared and they could be counted as
- * valid references during a kmemleak scan. Therefore, kmemleak must
- * not scan such objects.
- */
- kmemleak_no_scan(ac);
if (ac) {
ac->avail = 0;
ac->limit = limit;
@@ -589,6 +581,14 @@ static struct array_cache *alloc_arraycache(int node, int entries,
struct array_cache *ac = NULL;

ac = kmalloc_node(memsize, gfp, node);
+ /*
+ * The array_cache structures contain pointers to free object.
+ * However, when such objects are allocated or transferred to another
+ * cache the pointers are not cleared and they could be counted as
+ * valid references during a kmemleak scan. Therefore, kmemleak must
+ * not scan such objects.
+ */
+ kmemleak_no_scan(ac);
init_arraycache(ac, entries, batchcount);
return ac;
}
@@ -683,6 +683,7 @@ static struct alien_cache *__alloc_alien_cache(int node, int entries,

alc = kmalloc_node(memsize, gfp, node);
if (alc) {
+ kmemleak_no_scan(alc);
init_arraycache(&alc->ac, entries, batch);
spin_lock_init(&alc->lock);
}
--
2.19.1


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