Hi,
On 8/26/2023 5:23 PM, Björn Töpel wrote:
> Hou Tao <houtao@xxxxxxxxxxxxxxx> writes:
>
>> Hi,
>>
>> On 8/25/2023 11:28 PM, Yonghong Song wrote:
>>>
>>> On 8/25/23 3:32 AM, Björn Töpel wrote:
>>>> I'm chasing a workqueue hang on RISC-V/qemu (TCG), using the bpf
>>>> selftests on bpf-next 9e3b47abeb8f.
>>>>
>>>> I'm able to reproduce the hang by multiple runs of:
>>>> | ./test_progs -a link_api -a linked_list
>>>> I'm currently investigating that.
>>>>
>>>> But! Sometimes (every blue moon) I get a warn_on_once hit:
>>>> | ------------[ cut here ]------------
>>>> | WARNING: CPU: 3 PID: 261 at kernel/bpf/memalloc.c:342
>>>> bpf_mem_refill+0x1fc/0x206
>>>> | Modules linked in: bpf_testmod(OE)
>>>> | CPU: 3 PID: 261 Comm: test_progs-cpuv Tainted: G OE
>>>> N 6.5.0-rc5-01743-gdcb152bb8328 #2
>>>> | Hardware name: riscv-virtio,qemu (DT)
>>>> | epc : bpf_mem_refill+0x1fc/0x206
>>>> | ra : irq_work_single+0x68/0x70
>>>> | epc : ffffffff801b1bc4 ra : ffffffff8015fe84 sp : ff2000000001be20
>>>> | gp : ffffffff82d26138 tp : ff6000008477a800 t0 : 0000000000046600
>>>> | t1 : ffffffff812b6ddc t2 : 0000000000000000 s0 : ff2000000001be70
>>>> | s1 : ff5ffffffffe8998 a0 : ff5ffffffffe8998 a1 : ff600003fef4b000
>>>> | a2 : 000000000000003f a3 : ffffffff80008250 a4 : 0000000000000060
>>>> | a5 : 0000000000000080 a6 : 0000000000000000 a7 : 0000000000735049
>>>> | s2 : ff5ffffffffe8998 s3 : 0000000000000022 s4 : 0000000000001000
>>>> | s5 : 0000000000000007 s6 : ff5ffffffffe8570 s7 : ffffffff82d6bd30
>>>> | s8 : 000000000000003f s9 : ffffffff82d2c5e8 s10: 000000000000ffff
>>>> | s11: ffffffff82d2c5d8 t3 : ffffffff81ea8f28 t4 : 0000000000000000
>>>> | t5 : ff6000008fd28278 t6 : 0000000000040000
>>>> | status: 0000000200000100 badaddr: 0000000000000000 cause:
>>>> 0000000000000003
>>>> | [<ffffffff801b1bc4>] bpf_mem_refill+0x1fc/0x206
>>>> | [<ffffffff8015fe84>] irq_work_single+0x68/0x70
>>>> | [<ffffffff8015feb4>] irq_work_run_list+0x28/0x36
>>>> | [<ffffffff8015fefa>] irq_work_run+0x38/0x66
>>>> | [<ffffffff8000828a>] handle_IPI+0x3a/0xb4
>>>> | [<ffffffff800a5c3a>] handle_percpu_devid_irq+0xa4/0x1f8
>>>> | [<ffffffff8009fafa>] generic_handle_domain_irq+0x28/0x36
>>>> | [<ffffffff800ae570>] ipi_mux_process+0xac/0xfa
>>>> | [<ffffffff8000a8ea>] sbi_ipi_handle+0x2e/0x88
>>>> | [<ffffffff8009fafa>] generic_handle_domain_irq+0x28/0x36
>>>> | [<ffffffff807ee70e>] riscv_intc_irq+0x36/0x4e
>>>> | [<ffffffff812b5d3a>] handle_riscv_irq+0x54/0x86
>>>> | [<ffffffff812b6904>] do_irq+0x66/0x98
>>>> | ---[ end trace 0000000000000000 ]---
>>>>
>>>> Code:
>>>> | static void free_bulk(struct bpf_mem_cache *c)
>>>> | {
>>>> | struct bpf_mem_cache *tgt = c->tgt;
>>>> | struct llist_node *llnode, *t;
>>>> | unsigned long flags;
>>>> | int cnt;
>>>> |
>>>> | WARN_ON_ONCE(tgt->unit_size != c->unit_size);
>>>> | ...
>>>>
>>>> I'm not well versed in the memory allocator; Before I dive into it --
>>>> has anyone else hit it? Ideas on why the warn_on_once is hit?
>>> Maybe take a look at the patch
>>> 822fb26bdb55 bpf: Add a hint to allocated objects.
>>>
>>> In the above patch, we have
>>>
>>> + /*
>>> + * Remember bpf_mem_cache that allocated this object.
>>> + * The hint is not accurate.
>>> + */
>>> + c->tgt = *(struct bpf_mem_cache **)llnode;
>>>
>>> I suspect that the warning may be related to the above.
>>> I tried the above ./test_progs command line (running multiple
>>> at the same time) and didn't trigger the issue.
>> The extra 8-bytes before the freed pointer is used to save the pointer
>> of the original bpf memory allocator where the freed pointer came from,
>> so unit_free() could free the pointer back to the original allocator to
>> prevent alloc-and-free unbalance.
>>
>> I suspect that a wrong pointer was passed to bpf_obj_drop, but do not
>> find anything suspicious after checking linked_list. Another possibility
>> is that there is write-after-free problem which corrupts the extra
>> 8-bytes before the freed pointer. Could you please apply the following
>> debug patch to check whether or not the extra 8-bytes are corrupted ?
> Thanks for getting back!
>
> I took your patch for a run, and there's a hit:
> | bad cache ff5ffffffffe8570: got size 96 work ffffffff801b19c8, cache ff5ffffffffe8980 exp size 128 work ffffffff801b19c8
The extra 8-bytes are not corrupted. Both of these two bpf_mem_cache are
valid and there are in the cache array defined in bpf_mem_caches. BPF
memory allocator allocated the pointer from 96-bytes sized-cache, but it
tried to free the pointer through 128-bytes sized-cache.
Now I suspect there is no 96-bytes slab in your system and ksize(ptr -
LLIST_NODE_SZ) returns 128, so bpf memory allocator selected the
128-byte sized-cache instead of 96-bytes sized-cache. Could you please
check the value of KMALLOC_MIN_SIZE in your kernel .config and using the
following command to check whether there is 96-bytes slab in your system:
$ cat /proc/slabinfo |grep kmalloc-96
dma-kmalloc-96 0 0 96 42 1 : tunables 0 0
0 : slabdata 0 0 0
kmalloc-96 1865 2268 96 42 1 : tunables 0 0
0 : slabdata 54 54 0
In my system, slab has 96-bytes cached, so grep outputs something, but I
think there will no output in your system.
> | WARNING: CPU: 3 PID: 265 at kernel/bpf/memalloc.c:847 bpf_mem_free+0xb2/0xe0
> | ---[ end trace 0000000000000000 ]---
> | 00000000: 80 e3 dc 85 00 00 60 ff 00 00 00 00 00 00 00 00
> | 00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 00000020: 20 00 00 00 00 00 00 00 c8 19 1b 80 ff ff ff ff
> | 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 00000040: 60 00 00 00 33 00 00 00 20 00 00 00 60 00 00 00
> | 00000050: 30 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 00000060: 70 85 fe ff ff ff 5f ff 00 00 00 00 00 00 00 00
> | 00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 00000090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 000000a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 000000b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | 000000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> | WARNING: CPU: 2 PID: 265 at kernel/bpf/memalloc.c:342 bpf_mem_refill+0x1fc/0x206
> | ---[ end trace 0000000000000000 ]---
>
>
> Björn
