On Wed, Feb 19, 2020 at 11:31:06AM -0800, Yonghong Song wrote:
> Commit 057996380a42 ("bpf: Add batch ops to all htab bpf map")
> added lookup_and_delete batch operation for hash table.
> The current implementation has bpf_lru_push_free() inside
> the bucket lock, which may cause a deadlock.
>
> syzbot reports:
> -> #2 (&htab->buckets[i].lock#2){....}:
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
> htab_lru_map_delete_node+0xce/0x2f0 kernel/bpf/hashtab.c:593
> __bpf_lru_list_shrink_inactive kernel/bpf/bpf_lru_list.c:220 [inline]
> __bpf_lru_list_shrink+0xf9/0x470 kernel/bpf/bpf_lru_list.c:266
> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:340 [inline]
> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
> bpf_lru_pop_free+0x87c/0x1670 kernel/bpf/bpf_lru_list.c:499
> prealloc_lru_pop+0x2c/0xa0 kernel/bpf/hashtab.c:132
> __htab_lru_percpu_map_update_elem+0x67e/0xa90 kernel/bpf/hashtab.c:1069
> bpf_percpu_hash_update+0x16e/0x210 kernel/bpf/hashtab.c:1585
> bpf_map_update_value.isra.0+0x2d7/0x8e0 kernel/bpf/syscall.c:181
> generic_map_update_batch+0x41f/0x610 kernel/bpf/syscall.c:1319
> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
> __do_sys_bpf+0x9b7/0x41e0 kernel/bpf/syscall.c:3460
> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> -> #0 (&loc_l->lock){....}:
> check_prev_add kernel/locking/lockdep.c:2475 [inline]
> check_prevs_add kernel/locking/lockdep.c:2580 [inline]
> validate_chain kernel/locking/lockdep.c:2970 [inline]
> __lock_acquire+0x2596/0x4a00 kernel/locking/lockdep.c:3954
> lock_acquire+0x190/0x410 kernel/locking/lockdep.c:4484
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x95/0xcd kernel/locking/spinlock.c:159
> bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline]
> bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555
> __htab_map_lookup_and_delete_batch+0x8d4/0x1540 kernel/bpf/hashtab.c:1374
> htab_lru_map_lookup_and_delete_batch+0x34/0x40 kernel/bpf/hashtab.c:1491
> bpf_map_do_batch+0x3f5/0x510 kernel/bpf/syscall.c:3348
> __do_sys_bpf+0x1f7d/0x41e0 kernel/bpf/syscall.c:3456
> __se_sys_bpf kernel/bpf/syscall.c:3355 [inline]
> __x64_sys_bpf+0x73/0xb0 kernel/bpf/syscall.c:3355
> do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
>
> Possible unsafe locking scenario:
>
> CPU0 CPU2
> ---- ----
> lock(&htab->buckets[i].lock#2);
> lock(&l->lock);
> lock(&htab->buckets[i].lock#2);
> lock(&loc_l->lock);
>
> *** DEADLOCK ***
>
> To fix the issue, for htab_lru_map_lookup_and_delete_batch() in CPU0,
> let us do bpf_lru_push_free() out of the htab bucket lock. This can
> avoid the above deadlock scenario.
>
> Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map")
> Reported-by: syzbot+a38ff3d9356388f2fb83@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+122b5421d14e68f29cd1@xxxxxxxxxxxxxxxxxxxxxxxxx
> Suggested-by: Hillf Danton <hdanton@xxxxxxxx>
> Suggested-by: Martin KaFai Lau <kafai@xxxxxx>
> Acked-by: Brian Vazquez <brianvv@xxxxxxxxxx>
> Reviewed-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> Signed-off-by: Yonghong Song <yhs@xxxxxx>
> ---
> kernel/bpf/hashtab.c | 34 +++++++++++++++++++++++++++++++---
> 1 file changed, 31 insertions(+), 3 deletions(-)
>
> Changelog:
> v2 -> v3:
> . changed variable name, fixed reverse Christmas tree
> coding style and added more comments, from Martin.
Acked-by: Martin KaFai Lau <kafai@xxxxxx>
