Description of problem:
I logged out of Plasma 5.15.5 on Wayland. sddm didn't show up and the screen stayed blank which I've seen many times before when logging out of Plasma on Wayland. I pressed sysrq+alt+e , sysrq+alt+i which terminated then killed most of the user-space processes. sddm restarted after that.

This segmentation fault occurred at about the same time that the screen went blank. coredumpctl gdb showed that  tc_victim->fd in _int_malloc at malloc.c:3623 was an inaccessible address.
Core was generated by `/usr/libexec/org_kde_powerdevil'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x00007f0d44dcadac in _int_malloc (av=av@entry=0x7f0d2c000020, bytes=bytes@entry=65)
    at malloc.c:3622
3622                          if (SINGLE_THREAD_P)
[Current thread is 1 (Thread 0x7f0d33b86700 (LWP 1559))]

(gdb) list
3617
3618                      /* While bin not empty and tcache not full, copy chunks.  */
3619                      while (tcache->counts[tc_idx] < mp_.tcache_count
3620                             && (tc_victim = *fb) != NULL)
3621                        {
3622                          if (SINGLE_THREAD_P)
3623                            *fb = tc_victim->fd;
3624                          else
3625                            {
3626                              REMOVE_FB (fb, pp, tc_victim);

(gdb) p tc_victim->fd
Cannot access memory at address 0xa10000556b
(gdb) p tc_victim
$2 = (mchunkptr) 0xa10000555b

A signal indicating a crash appeared after #13 in tcache_get at malloc.c:2952. Some kind of string conversions involving "org.kde.kglobalaccel" happened at #16-19.

The segmentation faults and invalid reads and writes of powerdevil when logging out of Plasma on Wayland at https://bugzilla.redhat.com/show_bug.cgi?id=1713467 might be related.
The report I made about those crashes at https://bugs.kde.org/show_bug.cgi?id=408553 was reassigned to kwin, wayland-generic. 

Version-Release number of selected component:
powerdevil-5.15.5-1.fc30

Additional info:
reporter:       libreport-2.10.1
backtrace_rating: 3
cmdline:        /usr/libexec/org_kde_powerdevil
crash_function: QArrayData::allocate
executable:     /usr/libexec/org_kde_powerdevil
journald_cursor: s=45e2a08c6064454f9bd0b47d6f9f1c62;i=605b1;b=b6c057b14b934dd099bed2505b0083f4;m=735de165;t=58cfde06c3d7e;x=e53858adb62254f3
kernel:         5.1.16-300.fc30.x86_64
rootdir:        /
runlevel:       N 5
type:           CCpp
uid:            1000