Messages in this thread | | | Subject | Re: possible deadlock in bpf_lru_push_free | From | Yonghong Song <> | Date | Tue, 18 Feb 2020 09:44:39 -0800 |
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On 2/16/20 9:23 PM, Hillf Danton wrote: > > On Sun, 16 Feb 2020 04:17:09 -0800 >> syzbot has found a reproducer for the following crash on: >> >> HEAD commit: 2019fc96 Merge git://git.kernel.org/pub/scm/linux/kernel/g.. >> git tree: net >> console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D1358bb11e00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=zrgWcBnddWkMWG2zm-9nC8EwvHMsuqw_-EEXwl23XLg&e= >> kernel config: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D735296e4dd620b10&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=kbT6Yw89JDoIWSQtlLJ7sjyNoP2Ulud27GNorna1zQk&e= >> dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D122b5421d14e68f29cd1&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=U3pdUmrcroaeNsJ9DgFbTlvftQUCUcJ1CW_0NxS8yGA&e= >> compiler: gcc (GCC) 9.0.0 20181231 (experimental) >> syz repro: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_repro.syz-3Fx-3D14b67d6ee00000&d=DwIDAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=npe_gMkFnfxt6F5dGLs6zsNHWkYM30LkMFOk1_ZR1w8&s=TuSfjosRFQW3ArpQwikTtx-dgLLBSMgJfVKtUltqQBM&e= >> >> IMPORTANT: if you fix the bug, please add the following tag to the commit: >> Reported-by: syzbot+122b5421d14e68f29cd1@syzkaller.appspotmail.com >> >> ====================================================== >> WARNING: possible circular locking dependency detected >> 5.6.0-rc1-syzkaller #0 Not tainted >> ------------------------------------------------------ >> syz-executor.4/13544 is trying to acquire lock: >> ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_common_lru_push_free kernel/bpf/bpf_lru_list.c:516 [inline] >> ffffe8ffffcba0b8 (&loc_l->lock){....}, at: bpf_lru_push_free+0x250/0x5b0 kernel/bpf/bpf_lru_list.c:555 >> >> but task is already holding lock: >> ffff888094985960 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322 >> >> which lock already depends on the new lock. >> >> >> the existing dependency chain (in reverse order) is: >> >> -> #2 (&htab->buckets[i].lock){....}: >> __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 >> >> -> #1 (&l->lock){....}: >> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline] >> _raw_spin_lock+0x2f/0x40 kernel/locking/spinlock.c:151 >> bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:325 [inline] >> bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline] >> bpf_lru_pop_free+0x67f/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 >> >> other info that might help us debug this: >> >> Chain exists of: >> &loc_l->lock --> &l->lock --> &htab->buckets[i].lock >> >> Possible unsafe locking scenario: >> >> CPU0 CPU1 >> ---- ---- >> lock(&htab->buckets[i].lock); >> lock(&l->lock); >> lock(&htab->buckets[i].lock); >> lock(&loc_l->lock); >> >> *** DEADLOCK *** >> >> 2 locks held by syz-executor.4/13544: >> #0: ffffffff89bac240 (rcu_read_lock){....}, at: __htab_map_lookup_and_delete_batch+0x54b/0x1540 kernel/bpf/hashtab.c:1308 >> #1: ffff888094985960 (&htab->buckets[i].lock){....}, at: __htab_map_lookup_and_delete_batch+0x617/0x1540 kernel/bpf/hashtab.c:1322 >> >> stack backtrace: >> CPU: 0 PID: 13544 Comm: syz-executor.4 Not tainted 5.6.0-rc1-syzkaller #0 >> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 >> Call Trace: >> __dump_stack lib/dump_stack.c:77 [inline] >> dump_stack+0x197/0x210 lib/dump_stack.c:118 >> print_circular_bug.isra.0.cold+0x163/0x172 kernel/locking/lockdep.c:1684 >> check_noncircular+0x32e/0x3e0 kernel/locking/lockdep.c:1808 >> 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 > > Reclaim hash table elememt outside bucket lock.
Thanks for the following patch. Yes, we do have an potential issue with the above deadlock if LRU hash map is not preallocated.
I am not a RCU expert, but maybe you could you help clarify one thing below?
> > --- a/kernel/bpf/hashtab.c > +++ b/kernel/bpf/hashtab.c > @@ -1259,6 +1259,7 @@ __htab_map_lookup_and_delete_batch(struc > u64 elem_map_flags, map_flags; > struct hlist_nulls_head *head; > struct hlist_nulls_node *n; > + struct hlist_nulls_node *node_to_free = NULL; > unsigned long flags; > struct htab_elem *l; > struct bucket *b; > @@ -1370,9 +1371,10 @@ again_nocopy: > } > 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) { > + l->hash_node.next = node_to_free; > + node_to_free = &l->hash_node;
Here, we change "next" pointer. How does this may impact the existing parallel map lookup which does not need to take bucket pointer?
> + } else > free_htab_elem(htab, l); > } > dst_key += key_size; > @@ -1380,6 +1382,12 @@ again_nocopy: > } > > raw_spin_unlock_irqrestore(&b->lock, flags); > + > + while (node_to_free) { > + l = container_of(node_to_free, struct htab_elem, hash_node); > + node_to_free = node_to_free->next; > + bpf_lru_push_free(&htab->lru, &l->lru_node); > + } > /* If we are not copying data, we can go to next bucket and avoid > * unlocking the rcu. > */ >
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