Re: Possible regression in "slab, slub: skip unnecessary kasan_cache_shutdown()"

[Jason A. Donenfeld]

On Tue, Jun 19, 2018 at 7:06 AM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:
> Currently refcnt in your
> code can underflow, through it does not seem like the selftest will
> cause the underflow but still you should fix it.

Indeed, and if this happened this would be a bug in the caller, not
the ratelimiter itself, kind of like lock imbalances; however it's
easy to mitigate this by just replacing that atomic64_dec_return with
atomic64_dec_if_positive, so I'll do that. Thanks for the suggestion.

> From high level your code seems fine. Does the issue occur on first
> try of selftest? Basically I wanted to ask if kmem_cache_destroy of
> your entry_cache was ever executed

Yes, it is.

> and have you tried to run this
> selftest multiple time while the system was up.

Interesting, it crashes on the second run of it, when executing
`KMEM_CACHE(ratelimiter_entry, 0)`. (OOPS is below.)

> As Dmitry already asked, are you using SLAB or SLUB?

SLUB.

> Sorry, I can not really give a definitive answer.

Alright, we'll poke it from both ends, then.

Crash on second run:
[    1.648240] general protection fault: 0000 [#1] PREEMPT SMP
DEBUG_PAGEALLOC KASAN
[    1.648240] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.17.2 #51
[    1.648240] RIP: 0010:__lock_acquire+0x9a9/0x3430
[    1.648240] RSP: 0000:ffff8800003b76a0 EFLAGS: 00010006
[    1.648240] RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 0000000000000000
[    1.648240] RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000001
[    1.648240] RBP: ffff8800003a8000 R08: 0000000000000001 R09: 0000000000000000
[    1.648240] R10: 0000000000000001 R11: ffffffff828c69e3 R12: 0000000000000001
[    1.648240] R13: 0000000000000018 R14: 0000000000000000 R15: ffff8800003a8000
[    1.648240] FS:  0000000000000000(0000) GS:ffff880036400000(0000)
knlGS:000000000
[    1.648240] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.648240] CR2: 0000000000000000 CR3: 0000000002220001 CR4: 00000000001606b0
[    1.660020] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[    1.660020] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[    1.660020] Call Trace:
[    1.660020]  ? _raw_spin_unlock_irqrestore+0x4a/0x90
[    1.660020]  ? debug_check_no_locks_held+0xb0/0xb0
[    1.660020]  ? depot_save_stack.cold.2+0x1e/0x1e
[    1.660020]  ? handle_null_ptr_deref+0x178/0x1f0
[    1.660020]  ? depot_save_stack.cold.2+0x1e/0x1e
[    1.660020]  ? _raw_spin_unlock+0x32/0x70
[    1.660020]  lock_acquire+0xf4/0x240
[    1.660020]  ? __slab_free.isra.11+0x1db/0x770
[    1.660020]  ? __slab_free.isra.11+0x1db/0x770
[    1.660020]  _raw_spin_lock_irqsave+0x4b/0x70
[    1.660020]  ? __slab_free.isra.11+0x1db/0x770
[    1.660020]  __slab_free.isra.11+0x1db/0x770
[    1.660020]  ? __free_pages_ok+0x49a/0xd10
[    1.660020]  ? mark_held_locks+0xdf/0x1b0
[    1.660020]  ? _raw_spin_unlock_irqrestore+0x61/0x90
[    1.660020]  ? qlist_free_all+0x58/0x1c0
[    1.660020]  qlist_free_all+0x70/0x1c0
[    1.660020]  ? trace_hardirqs_on_caller+0x3d0/0x630
[    1.660020]  quarantine_reduce+0x221/0x310
[    1.660020]  kasan_kmalloc+0x95/0xc0
[    1.660020]  kmem_cache_alloc+0x167/0x2e0
[    1.660020]  ? do_one_initcall+0x104/0x232
[    1.660020]  create_object+0xa7/0xa70
[    1.660020]  ? kmemleak_disable+0x90/0x90
[    1.660020]  ? quarantine_reduce+0x207/0x310
[    1.660020]  ? fs_reclaim_acquire.part.15+0x30/0x30
[    1.660020]  kmem_cache_alloc_node+0x209/0x340
[    1.660020]  __kmem_cache_create+0xe6/0x5c0
[    1.660020]  kmem_cache_create_usercopy+0x1ef/0x380
[    1.660020]  ? length_mt_init+0x11/0x11
[    1.660020]  kmem_cache_create+0xd/0x10
[    1.660020]  ratelimiter_init+0x4a/0x1e0
[    1.660020]  ratelimiter_selftest+0x13/0x9ec
[    1.660020]  ? length_mt_init+0x11/0x11
[    1.660020]  mod_init+0xb/0xa5
[    1.660020]  do_one_initcall+0x104/0x232
[    1.660020]  ? start_kernel+0x62c/0x62c
[    1.660020]  ? up_write+0x78/0x220
[    1.660020]  ? up_read+0x130/0x130
[    1.660020]  ? kasan_unpoison_shadow+0x30/0x40
[    1.660020]  kernel_init_freeable+0x3e8/0x48c
[    1.660020]  ? rest_init+0x2bf/0x2bf
[    1.660020]  kernel_init+0x7/0x121
[    1.660020]  ? rest_init+0x2bf/0x2bf
[    1.660020]  ret_from_fork+0x24/0x30
[    1.660020] Code: 81 c4 40 01 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f
c3 4d 85 ed 0f
[    1.660020] RIP: __lock_acquire+0x9a9/0x3430 RSP: ffff8800003b76a0
[    1.660020] ---[ end trace daba3b506c5594e5 ]---