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HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: JDg3vi0OLPDSXxL2p/oCmzDvUXOHbkr/XwuT93/NroojRBjhPcD5aDP47yjL0rVl X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3400 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-02-19_04:2020-02-19,2020-02-19 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 impostorscore=0 spamscore=0 phishscore=0 bulkscore=0 malwarescore=0 mlxlogscore=999 mlxscore=0 suspectscore=2 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2002190131 X-FB-Internal: deliver Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Feb 19, 2020 at 08:23:01AM -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. Patch looks good. Some minor comments. > > Fixes: 057996380a42 ("bpf: Add batch ops to all htab bpf map") > Reported-by: syzbot+a38ff3d9356388f2fb83@syzkaller.appspotmail.com > Reported-by: syzbot+122b5421d14e68f29cd1@syzkaller.appspotmail.com > Suggested-by: Hillf Danton > Suggested-by: Martin KaFai Lau > Acked-by: Brian Vazquez > Reviewed-by: Jakub Sitnicki > Signed-off-by: Yonghong Song > --- > kernel/bpf/hashtab.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > Changelog: > v1 -> v2: > . coding style fix to have braces in both then and else > branch, from Jakub. > > diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c > index 2d182c4ee9d9..a6e0d6aace62 100644 > --- a/kernel/bpf/hashtab.c > +++ b/kernel/bpf/hashtab.c > @@ -56,6 +56,7 @@ struct htab_elem { > union { > struct bpf_htab *htab; > struct pcpu_freelist_node fnode; > + struct htab_elem *link; Considering this usage is very specific, the name "link" sounds a bit general. May be "batch_free_link" or "batch_flink"? > }; > }; > }; > @@ -1255,6 +1256,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map, > void __user *uvalues = u64_to_user_ptr(attr->batch.values); > void __user *ukeys = u64_to_user_ptr(attr->batch.keys); > void *ubatch = u64_to_user_ptr(attr->batch.in_batch); > + struct htab_elem *node_to_free = NULL; Reverse xmas tree ordering. > u32 batch, max_count, size, bucket_size; > u64 elem_map_flags, map_flags; > struct hlist_nulls_head *head; > @@ -1370,16 +1372,28 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map, > } > if (do_delete) { > hlist_nulls_del_rcu(&l->hash_node); > - if (is_lru_map) > - bpf_lru_push_free(&htab->lru, &l->lru_node); > - else > + if (is_lru_map) { > + /* link to-be-freed elements together so > + * they can freed outside bucket lock region. > + */ Thanks for the comments here. I think a bit more details will be useful in the future. May be adding the details to the existing htab_lru_map_delete_elem() which is also using a similar lock strategy, e.g.: /* The LRU list has a lock (lru_lock). Each bucket of htab has a * lock (buck_lock). If both locks need to be acquired together, * the lock order is always lru_lock -> buck_lock and this only * happens in the bpf_lru_list.c logic. * * In hashtab.c, to avoid deadlock casued by lock ordering, * both locks are not acquired together (i.e. one lock is always * released first before acquiring another lock). */ static int htab_lru_map_delete_elem(struct bpf_map *map, void *key) { /* ... */ } and refer them here from here (__htab_map_lookup_and_delete_batch). > + l->link = node_to_free; > + node_to_free = l; > + } else { > free_htab_elem(htab, l); > + } > } [ ... ]