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    Subject[PATCH] slab: kmemleak no scan alien caches
    Date
    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 later by lifting kmemleak_no_scan()
    out of init_arraycache().

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

    [ 32.258841] kmemleak: Found object by alias at 0xffff8007b9aa7e38
    [ 32.258847] CPU: 190 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc2+ #2
    [ 32.258851] Call trace:
    [ 32.258858] dump_backtrace+0x0/0x168
    [ 32.258863] show_stack+0x24/0x30
    [ 32.258868] dump_stack+0x88/0xb0
    [ 32.258873] lookup_object+0x84/0xac
    [ 32.258877] find_and_get_object+0x84/0xe4
    [ 32.258882] kmemleak_no_scan+0x74/0xf4
    [ 32.258887] setup_kmem_cache_node+0x2b4/0x35c
    [ 32.258892] __do_tune_cpucache+0x250/0x2d4
    [ 32.258896] do_tune_cpucache+0x4c/0xe4
    [ 32.258901] enable_cpucache+0xc8/0x110
    [ 32.258905] setup_cpu_cache+0x40/0x1b8
    [ 32.258909] __kmem_cache_create+0x240/0x358
    [ 32.258913] create_cache+0xc0/0x198
    [ 32.258918] kmem_cache_create_usercopy+0x158/0x20c
    [ 32.258922] kmem_cache_create+0x50/0x64
    [ 32.258928] fsnotify_init+0x58/0x6c
    [ 32.258932] do_one_initcall+0x194/0x388
    [ 32.258937] kernel_init_freeable+0x668/0x688
    [ 32.258941] kernel_init+0x18/0x124
    [ 32.258946] ret_from_fork+0x10/0x18
    [ 32.258950] kmemleak: Object 0xffff8007b9aa7e00 (size 256):
    [ 32.258954] kmemleak: comm "swapper/0", pid 1, jiffies 4294697137
    [ 32.258958] kmemleak: min_count = 1
    [ 32.258962] kmemleak: count = 0
    [ 32.258965] kmemleak: flags = 0x1
    [ 32.258969] kmemleak: checksum = 0
    [ 32.258972] kmemleak: backtrace:
    [ 32.258977] kmemleak_alloc+0x84/0xb8
    [ 32.258982] kmem_cache_alloc_node_trace+0x31c/0x3a0
    [ 32.258987] __kmalloc_node+0x58/0x78
    [ 32.258991] setup_kmem_cache_node+0x26c/0x35c
    [ 32.258996] __do_tune_cpucache+0x250/0x2d4
    [ 32.259001] do_tune_cpucache+0x4c/0xe4
    [ 32.259005] enable_cpucache+0xc8/0x110
    [ 32.259010] setup_cpu_cache+0x40/0x1b8
    [ 32.259014] __kmem_cache_create+0x240/0x358
    [ 32.259018] create_cache+0xc0/0x198
    [ 32.259022] kmem_cache_create_usercopy+0x158/0x20c
    [ 32.259026] kmem_cache_create+0x50/0x64
    [ 32.259031] fsnotify_init+0x58/0x6c
    [ 32.259035] do_one_initcall+0x194/0x388
    [ 32.259039] kernel_init_freeable+0x668/0x688
    [ 32.259043] kernel_init+0x18/0x124
    [ 32.259048] kmemleak: Not scanning unknown object at 0xffff8007b9aa7e38
    [ 32.259052] CPU: 190 PID: 1 Comm: swapper/0 Not tainted 5.0.0-rc2+ #2
    [ 32.259056] Call trace:
    [ 32.259060] dump_backtrace+0x0/0x168
    [ 32.259065] show_stack+0x24/0x30
    [ 32.259070] dump_stack+0x88/0xb0
    [ 32.259074] kmemleak_no_scan+0x90/0xf4
    [ 32.259078] setup_kmem_cache_node+0x2b4/0x35c
    [ 32.259083] __do_tune_cpucache+0x250/0x2d4
    [ 32.259088] do_tune_cpucache+0x4c/0xe4
    [ 32.259092] enable_cpucache+0xc8/0x110
    [ 32.259096] setup_cpu_cache+0x40/0x1b8
    [ 32.259100] __kmem_cache_create+0x240/0x358
    [ 32.259104] create_cache+0xc0/0x198
    [ 32.259108] kmem_cache_create_usercopy+0x158/0x20c
    [ 32.259112] kmem_cache_create+0x50/0x64
    [ 32.259116] fsnotify_init+0x58/0x6c
    [ 32.259120] do_one_initcall+0x194/0x388
    [ 32.259125] kernel_init_freeable+0x668/0x688
    [ 32.259129] kernel_init+0x18/0x124
    [ 32.259133] ret_from_fork+0x10/0x18

    Fixes: 1fe00d50a9e8 (slab: factor out initialization of array cache)
    Signed-off-by: Qian Cai <cai@lca.pw>
    ---
    mm/slab.c | 17 +++++++++--------
    1 file changed, 9 insertions(+), 8 deletions(-)

    diff --git a/mm/slab.c b/mm/slab.c
    index 78eb8c5bf4e4..0aff454f007b 100644
    --- a/mm/slab.c
    +++ b/mm/slab.c
    @@ -550,14 +550,6 @@ 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;
    @@ -573,6 +565,14 @@ 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;
    }
    @@ -667,6 +667,7 @@ 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);
    }
    --
    2.17.2 (Apple Git-113)
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