Hi Neil,
> This is the problem. 'hold' hasn't been initialised.
> We could either do:
> bio_list_init(&hold);
> bio_list_merge(&hold, &bio_list_on_stack);
I tried above variant first and it lead to panic in endio path:
PID: 4004 TASK: ffff8802337f3400 CPU: 1 COMMAND: "fio"
#0 [ffff88023ec838d0] machine_kexec at ffffffff8104075a
#1 [ffff88023ec83918] crash_kexec at ffffffff810d54c3
#2 [ffff88023ec839e0] oops_end at ffffffff81008784
#3 [ffff88023ec83a08] no_context at ffffffff8104a8f6
#4 [ffff88023ec83a60] __bad_area_nosemaphore at ffffffff8104abcf
#5 [ffff88023ec83aa8] bad_area_nosemaphore at ffffffff8104ad3e
#6 [ffff88023ec83ab8] __do_page_fault at ffffffff8104afd7
#7 [ffff88023ec83b10] do_page_fault at ffffffff8104b33c
#8 [ffff88023ec83b20] page_fault at ffffffff818173a2
[exception RIP: bio_check_pages_dirty+65]
RIP: ffffffff813f6221 RSP: ffff88023ec83bd8 RFLAGS: 00010212
RAX: 0000000000000020 RBX: ffff880232d75010 RCX: 0000000000000001
RDX: ffff880232d74000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88023ec83bf8 R8: 0000000000000001 R9: 0000000000000000
R10: ffffffff81f25ac0 R11: ffff8802348acef0 R12: 0000000000000001
R13: 0000000000000000 R14: ffff8800b53b7d00 R15: ffff88009704d180
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#9 [ffff88023ec83c00] dio_bio_complete at ffffffff811d010e
#10 [ffff88023ec83c38] dio_bio_end_aio at ffffffff811d0367
#11 [ffff88023ec83c68] bio_endio at ffffffff813f637a
#12 [ffff88023ec83c80] call_bio_endio at ffffffffa0868220 [raid1]
#13 [ffff88023ec83cc8] raid_end_bio_io at ffffffffa086885b [raid1]
#14 [ffff88023ec83cf8] raid1_end_read_request at ffffffffa086a184 [raid1]
#15 [ffff88023ec83d50] bio_endio at ffffffff813f637a
#16 [ffff88023ec83d68] blk_update_request at ffffffff813fdab6
#17 [ffff88023ec83da8] blk_mq_end_request at ffffffff81406dfe
> or just
> hold = bio_list_on_stack;
>
>
> You didn't find 'hold' to be necessary in your testing, but I think that
> is more complex arrangements it could make an important difference.
Could you elaborate a bit more, from my understanding, in later code,
we pop all bio from bio_list_on_stack,
add it to either "lower" or "same" bio_list, so merge both will have
the whole list again, right?
>
> Thanks,
> NeilBrown
>
>
>>> + bio_list_init(&bio_list_on_stack); ??? maybe init hold, and then merge bio_list_on_stack?
>>> ret = q->make_request_fn(q, bio);
>>>
>>> blk_queue_exit(q);
Thanks
--
Jinpu Wang
Linux Kernel Developer
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