[Devel] [RFC PATCH vz9 v6 44/62] dm-ploop: introduce pio runner threads

[Alexander Atanasov]

On 20.01.25 12:08, Pavel Tikhomirov wrote:
> 
> 
> On 12/6/24 05:56, Alexander Atanasov wrote:
>> +static inline int ploop_runners_add_work(struct ploop *ploop, struct 
>> pio *pio)
>> +{
>> +    int i;
>> +    struct ploop_worker *wrkr;
>> +
>> +    if (++ploop->last_used_runner >= ploop->nkt_runners)
>> +        ploop->last_used_runner = 0;
>> +    wrkr = ploop->kt_runners[ploop->last_used_runner];
> 
> This can potentially lead to out of bound read, as we don't have locks 
> around wrapping last_used_runner increment to zero (i.e. it's not 
> atomic), here we can see ploop->last_used_runner >= nkt_runners.

Reworked - runners are circular list - READ_ONCE/WRITE_ONCE used to 
switch to ->next /see updated patches/


> 
> Note: I see (in final version, with all patches applied) multiple stacks 
> which probably can run concurrently:
> 
>    +-< ploop_runners_add_work
>      +-< ploop_index_wb_submit
>      | +-< ploop_grow_relocate_cluster
>      | | +-< ploop_process_resize_cmd
>      | | | +-< ploop_resize
>      | | | | +-< ploop_message
>      | +-< ploop_grow_update_header
>      | | +-< ploop_process_resize_cmd
>      | | | +-< ploop_resize
>      | | | | +-< ploop_message
>      | +-< ploop_submit_metadata_writeback
>      | | +-< do_ploop_run_work
>      | | | +-< do_ploop_work
>      | | | +-< ploop_worker
>      +-< process_ploop_fsync_work
>      | +-< do_ploop_run_work
>      | | +-< do_ploop_work
>      | | +-< ploop_worker
>      +-< ploop_runners_add_work_list
>      | +-< do_ploop_run_work
>      | | +-< do_ploop_work
>      | | +-< ploop_worker
> 
>> +
>> +    atomic_inc(&ploop->kt_worker->inflight_pios);
>> +    llist_add((struct llist_node *)(&pio->list), &wrkr->work_llist);
>> +    wake_up_process(wrkr->task);
>> +
>> +    return 0;
>> +}
> 

-- 
Regards,
Alexander Atanasov