php7.4-fpm consumes 100% CPU and loops mremap() system call

Recently I have upgraded to the mainline Debian 10 backport kernel. This morning I've noticed that the web server is very slow, and inspection showed 100% CPU usage by php7.4-fpm:

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
13901 www-data  20   0  461632 240612  91188 R 100.0   0.5  37:09.65 php-fpm7.4
16105 root      20   0  154088 101800  19280 R 100.0   0.2   0:48.18 php
13792 www-data  20   0  460844 240328  91512 R 100.0   0.5  37:31.51 php-fpm7.4
13948 www-data  20   0  463308 243644  94548 R 100.0   0.5  37:16.08 php-fpm7.4
16040 username  20   0   11708  10196   4612 R 100.0   0.0   1:02.09 imap
13752 www-data  20   0  467348 247620  93176 R 100.0   0.5  38:39.73 php-fpm7.4
  739 clamav    20   0 2725056   2.3g  11028 S 100.0   4.8  52:25.38 clamd
13796 www-data  20   0  464888 247260  95524 R 100.0   0.5  39:00.51 php-fpm7.4

The traced php7.4-fpm process appears to be looping and executing only the mremap() system call:

mremap(0x7f48cb600000, 13074432, 13078528, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13078528, 13082624, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13082624, 13086720, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13086720, 13090816, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13090816, 13094912, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13094912, 13099008, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13099008, 13103104, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13103104, 13107200, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13107200, 13111296, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13111296, 13115392, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13115392, 13119488, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13119488, 13123584, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13123584, 13127680, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13127680, 13131776, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13131776, 13135872, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13135872, 13139968, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13139968, 13144064, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13144064, 13148160, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13148160, 13152256, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13152256, 13156352, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13156352, 13160448, 0) = 0x7f48cb600000
mremap(0x7f48cb600000, 13160448, 13164544, 0) = 0x7f48cb600000
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Version of php7.4-fpm is 1:7.4.33-5+0~20230409.78+debian10~1.gbpa1ea7f alongside PHP packages from https://packages.sury.org/php/ buster, updated Apr/12/2023.

No change in configuration was made.

Rebooting into 4.19.0-23-amd64 kernel 4.19.269-1 did not fix the issue.

ii linux-image-4.19.0-23-amd64 4.19.269-1

There was no change of the configuration in the last weak AFAICR.

I tried to boot into the 4.19.0-23 kernel, expecting that it could be the problem with BPO 5.10.127-2 kernel.

However, the 100% CPU usage by the fpm7.4-fpm and very slow web remained.