Re: [PATCH v6 0/5] Fix potential kernel panic when increase hardware queue

[Bart Van Assche <bvanassche@acm.org>]

On 2020-05-12 05:20, Weiping Zhang wrote:
> On Tue, May 12, 2020 at 8:09 PM Weiping Zhang <zwp10758@gmail.com> wrote:
>> I don't test block/030, since I don't pull blktest very often.

That's unfortunate ...

>> It's a different problem,
>> because the mapping cann't be reset when do fallback, so the
>> cpu[>=1] will point to a hctx(!=0).
>>
>>  it should be fixed by:
>>
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index bc34d6b572b6..d82cefb0474f 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -3365,8 +3365,8 @@ static void __blk_mq_update_nr_hw_queues(struct
>> blk_mq_tag_set *set,
>>                 goto reregister;
>>
>>         set->nr_hw_queues = nr_hw_queues;
>> -       blk_mq_update_queue_map(set);
>>  fallback:
>> +       blk_mq_update_queue_map(set);
>>         list_for_each_entry(q, &set->tag_list, tag_set_list) {
>>                 blk_mq_realloc_hw_ctxs(set, q);
>>                 if (q->nr_hw_queues != set->nr_hw_queues) {

If this is posted as a patch, feel free to add:

Tested-by: Bart van Assche <bvanassche@acm.org>

> And block/030 should also be improved ?
> 
>  35         # Since older null_blk versions do not allow "submit_queues" to be
>  36         # modified, check first whether that configs attribute is writeable.
>  37         # Each iteration of the loop below triggers $(nproc) + 1
>  38         # null_init_hctx() calls. Since <interval>=$(nproc), all possible
>  39         # blk_mq_realloc_hw_ctxs() error paths will be triggered. Whether or
>  40         # not this test succeeds depends on whether or not _check_dmesg()
>  41         # detects a kernel warning.
>  42         if { echo "$(<"$sq")" >$sq; } 2>/dev/null; then
>  43                 for ((i = 0; i < 100; i++)); do
>  44                         echo 1 > $sq
>  45                         nproc > $sq  # this line output lots
> "nproc: write error: Cannot allocate memory"
>  46                 done
>  47         else
>  48                 SKIP_REASON="Skipping test because $sq cannot be modified"
>  49         fi
> 
> 
> The test result show this test case [failed], actually it [pass],
> there is no warning detect
> in kernel log, if apply above patch.
> 
> block/030 (trigger the blk_mq_realloc_hw_ctxs() error path)  [failed]
>     runtime  1.999s  ...  2.115s
>     --- tests/block/030.out 2020-05-12 10:42:26.345782849 +0800
>     +++ /data1/zwp/src/blktests/results/nodev/block/030.out.bad
> 2020-05-12 20:14:59.878915218 +0800
>     @@ -1 +1,51 @@
>     +nproc: write error: Cannot allocate memory
>     +nproc: write error: Cannot allocate memory
>     +nproc: write error: Cannot allocate memory
>     +nproc: write error: Cannot allocate memory
>     +nproc: write error: Cannot allocate memory
>     +nproc: write error: Cannot allocate memory
>     +nproc: write error: Cannot allocate memory
>     ...
>     (Run 'diff -u tests/block/030.out
> /data1/zwp/src/blktests/results/nodev/block/030.out.bad' to see the
> entire diff)

That's weird. I have not yet encountered this. Test block/030 passes on
my setup.

Thanks,

Bart.