Bug 2086693

Created attachment 1880162 [details]
Patch for fixing busy loop in nfsrahead

On a fresh install of Fedora 36 systemd-udev-settle.service takes much time in comparison to earlier Fedora releases:

$ systemd-analyze blame | head -n2
2min 48ms systemd-udev-settle.service
  53.688s NetworkManager-wait-online.service

Further analyses shown that systemd-udev-settle.service invokes nfsrahead:

$ ps aux | grep nfs
root        79  0.0  0.0      0     0 ?        I<   21:21   0:00 [nfsiod]
root       585 91.3  0.0   1872   744 ?        R    21:25   0:11 /usr/libexec/nfsrahead btrfs-1
dw         856  0.0  0.1   7860  1856 pts/0    S+   21:25   0:00 grep --color=auto nfs

which seems to consume 100% of cpu:

$ top
top - 21:27:50 up 6 min,  2 users,  load average: 4.42, 4.74, 2.38
Tasks: 168 total,   2 running, 165 sleeping,   1 stopped,   0 zombie
%Cpu0  : 78.0 us,  3.4 sy,  0.0 ni,  1.7 id, 16.9 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu1  : 98.4 us,  1.6 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu2  : 69.1 us, 16.4 sy,  0.0 ni, 14.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu3  :100.0 us,  0.0 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :    920.4 total,      8.2 free,    413.9 used,    498.2 buff/cache
MiB Swap:    920.0 total,    919.5 free,      0.5 used.    490.3 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND    
  631 openhab   20   0  456896 235780  15848 S 242.6  25.0   4:31.53 java       
  585 root      20   0    1872    744    684 R 100.0   0.1   2:41.06 nfsrahead  

Under gdb it looks like it busy loops in getopt():

$ gdb /usr/libexec/nfsrahead 
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Reading symbols from /usr/libexec/nfsrahead...
Reading symbols from /usr/lib/debug/usr/libexec/nfsrahead-2.6.1-2.rc4.fc36.arm.debug...
(gdb) bt
No stack.
(gdb) r
Starting program: /usr/libexec/nfsrahead 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/libthread_db.so.1".

Program received signal SIGINT, Interrupt.
0x76f16e8c in _getopt_internal (argc=1, argv=0x7efffa14, optstring=0x4006c4 "dF", longopts=longopts@entry=0x0, longind=longind@entry=0x0, long_only=long_only@entry=0, posixly_correct=posixly_correct@entry=0) at getopt.c:708
708	  getopt_data.optind = optind;
(gdb) bt
#0  0x76f16e8c in _getopt_internal (argc=1, argv=0x7efffa14, 
    optstring=0x4006c4 "dF", longopts=longopts@entry=0x0, 
    longind=longind@entry=0x0, long_only=long_only@entry=0, 
    posixly_correct=posixly_correct@entry=0) at getopt.c:708
#1  0x76f16f38 in getopt (argc=<optimized out>, argv=<optimized out>, 
    optstring=<optimized out>) at getopt.c:735
#2  0x004004b8 in main (argc=1, argv=0x7efffa14) at main.c:145
(gdb) n
709	  getopt_data.opterr = opterr;
(gdb) 
711	  result = _getopt_internal_r (argc, argv, optstring, longopts,
(gdb) 
715	  optind = getopt_data.optind;
(gdb) 
716	  optarg = getopt_data.optarg;
(gdb) 
717	  optopt = getopt_data.optopt;
(gdb) 
719	  return result;
(gdb) 
main (argc=1, argv=0x7efffa14) at main.c:146
146			switch (opt) {
(gdb) 
145		while((opt = getopt(argc, argv, "dF")) != -1) {
(gdb) 
146			switch (opt) {
(gdb) 
145		while((opt = getopt(argc, argv, "dF")) != -1) {
(gdb) 
146			switch (opt) {
(gdb) 
145		while((opt = getopt(argc, argv, "dF")) != -1) {
(gdb) 
146			switch (opt) {
(gdb) 
145		while((opt = getopt(argc, argv, "dF")) != -1) {
(gdb) 
146			switch (opt) {
(gdb) 
145		while((opt = getopt(argc, argv, "dF")) != -1) {
(gdb) 
146			switch (opt) {
(gdb) 
145		while((opt = getopt(argc, argv, "dF")) != -1) {
(gdb) 
146			switch (opt) {
(gdb) 

with the attached patch the boot time becomes again comparable to earlier Fedora releases:

$ systemd-analyze blame | head -n4
11.213s grafana-server.service
 8.106s firewalld.service
 7.033s NetworkManager-wait-online.service
 5.326s systemd-udev-settle.service

More precisely the systemd-udev-settle.service is executed by ~2min faster during the boot.

Versions involved:
$ rpm -qv systemd nfs-utils gcc
systemd-250.3-8.fc36.armv7hl
nfs-utils-2.6.1-2.rc4.fc36.armv7hl
gcc-12.1.1-1.fc36.armv7hl