Hello Vitaly Kuznetsov,
The patch b05d8d9ef5ef: "Drivers: hv: hv_balloon: eliminate the
trylock path in acquire/release_region_mutex" from Feb 28, 2015,
leads to the following static checker warning:
drivers/hv/hv_balloon.c:669 hv_mem_hot_add()
warn: 'mutex:&dm_device.ha_region_mutex' is sometimes locked here and sometimes unlocked.
drivers/hv/hv_balloon.c
609 static void hv_mem_hot_add(unsigned long start, unsigned long size,
610 unsigned long pfn_count,
611 struct hv_hotadd_state *has)
612 {
613 int ret = 0;
614 int i, nid;
615 unsigned long start_pfn;
616 unsigned long processed_pfn;
617 unsigned long total_pfn = pfn_count;
618
619 for (i = 0; i < (size/HA_CHUNK); i++) {
620 start_pfn = start + (i * HA_CHUNK);
621 has->ha_end_pfn += HA_CHUNK;
622
623 if (total_pfn > HA_CHUNK) {
624 processed_pfn = HA_CHUNK;
625 total_pfn -= HA_CHUNK;
626 } else {
627 processed_pfn = total_pfn;
628 total_pfn = 0;
629 }
630
631 has->covered_end_pfn += processed_pfn;
632
633 init_completion(&dm_device.ol_waitevent);
634 dm_device.ha_waiting = true;
635
636 mutex_unlock(&dm_device.ha_region_mutex);
637 nid = memory_add_physaddr_to_nid(PFN_PHYS(start_pfn));
638 ret = add_memory(nid, PFN_PHYS((start_pfn)),
639 (HA_CHUNK << PAGE_SHIFT));
640
641 if (ret) {
642 pr_info("hot_add memory failed error is %d\n", ret);
643 if (ret == -EEXIST) {
644 /*
645 * This error indicates that the error
646 * is not a transient failure. This is the
647 * case where the guest's physical address map
648 * precludes hot adding memory. Stop all further
649 * memory hot-add.
650 */
651 do_hot_add = false;
652 }
653 has->ha_end_pfn -= HA_CHUNK;
654 has->covered_end_pfn -= processed_pfn;
The callers assume we return with the lock held so they double unlock.
Probably double unlocking is not so terrible as double locking...
655 break;
656 }
657
658 /*
659 * Wait for the memory block to be onlined.
660 * Since the hot add has succeeded, it is ok to
661 * proceed even if the pages in the hot added region
662 * have not been "onlined" within the allowed time.
663 */
664 wait_for_completion_timeout(&dm_device.ol_waitevent, 5*HZ);
665 mutex_lock(&dm_device.ha_region_mutex);
666 post_status(&dm_device);
667 }
668
669 return;
670 }
regards,
dan carpenter
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