mlock fails with -1

[abpISCUE]

Environment

Windows build number: Microsoft Windows [Version 10.0.19042.870]
Your Distribution version: 10
Whether the issue is on WSL 2 and/or WSL 1: Linux version 5.4.72-microsoft-standard-WSL2 (oe-user@oe-host) (gcc version 8.2.0 (GCC)) #1 SMP Wed Oct 28 23:40:43 UTC 2020

Steps to reproduce

Eclipse project running in WSL, compiling with Eclipse, start executable in console or Eclipse,
the mlock command always returns -1:

#include <iostream>
#include <string.h>
#include <sys/mman.h>

static const size_t ALLOCATION_SIZE = (2 * 1024 * 1024);

int main() {
  std::cout << "Hello Test" << std::endl << std::flush;

  char* buffer = reinterpret_cast<char*>(malloc(ALLOCATION_SIZE));

  if (mlock(buffer, ALLOCATION_SIZE) == -1) {
    std::cout << "Locking memory failed: " << strerror(errno) << std::endl << std::flush;
  }
  return 0;
}

2619 execve("./Test", ["./Test"], 0x7ffe12f53fa8 /* 19 vars */) = 0
2619 brk(NULL) = 0x55d8240b7000
2619 access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
2619 openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
2619 fstat(3, {st_mode=S_IFREG|0644, st_size=82054, ...}) = 0
2619 mmap(NULL, 82054, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f5a4a293000
2619 close(3) = 0
2619 openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/libstdc++.so.6", O_RDONLY|O_CLOEXEC) = 3
2619 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\304\10\0\0\0\0\0"..., 832) = 832
2619 fstat(3, {st_mode=S_IFREG|0644, st_size=1570256, ...}) = 0
2619 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5a4a291000
2619 mmap(NULL, 1585184, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5a4a10d000
2619 mprotect(0x7f5a4a196000, 962560, PROT_NONE) = 0
2619 mmap(0x7f5a4a196000, 704512, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x89000) = 0x7f5a4a196000
2619 mmap(0x7f5a4a242000, 253952, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x135000) = 0x7f5a4a242000
2619 mmap(0x7f5a4a281000, 49152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x173000) = 0x7f5a4a281000
2619 mmap(0x7f5a4a28d000, 12320, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f5a4a28d000
2619 close(3) = 0
2619 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
2619 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\322\0\0\0\0\0\0"..., 832) = 832
2619 fstat(3, {st_mode=S_IFREG|0644, st_size=1579448, ...}) = 0
2619 mmap(NULL, 1581384, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5a49f8a000
2619 mmap(0x7f5a49f97000, 651264, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xd000) = 0x7f5a49f97000
2619 mmap(0x7f5a4a036000, 872448, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xac000) = 0x7f5a4a036000
2619 mmap(0x7f5a4a10b000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x180000) = 0x7f5a4a10b000
2619 close(3) = 0
2619 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = 3
2619 read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\3402\0\0\0\0\0\0"..., 832) = 832
2619 fstat(3, {st_mode=S_IFREG|0644, st_size=100712, ...}) = 0
2619 mmap(NULL, 103472, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5a49f70000
2619 mprotect(0x7f5a49f73000, 86016, PROT_NONE) = 0
2619 mmap(0x7f5a49f73000, 69632, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3000) = 0x7f5a49f73000
2619 mmap(0x7f5a49f84000, 12288, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x14000) = 0x7f5a49f84000
2619 mmap(0x7f5a49f88000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x7f5a49f88000
2619 close(3) = 0
2619 openat(AT_FDCWD, "/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
2619 read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260A\2\0\0\0\0\0"..., 832) = 832
2619 fstat(3, {st_mode=S_IFREG|0755, st_size=1824496, ...}) = 0
2619 mmap(NULL, 1837056, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f5a49daf000
2619 mprotect(0x7f5a49dd1000, 1658880, PROT_NONE) = 0
2619 mmap(0x7f5a49dd1000, 1343488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x22000) = 0x7f5a49dd1000
2619 mmap(0x7f5a49f19000, 311296, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x16a000) = 0x7f5a49f19000
2619 mmap(0x7f5a49f66000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b6000) = 0x7f5a49f66000
2619 mmap(0x7f5a49f6c000, 14336, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f5a49f6c000
2619 close(3) = 0
2619 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5a49dad000
2619 arch_prctl(ARCH_SET_FS, 0x7f5a49dadf40) = 0
2619 mprotect(0x7f5a49f66000, 16384, PROT_READ) = 0
2619 mprotect(0x7f5a49f88000, 4096, PROT_READ) = 0
2619 mprotect(0x7f5a4a10b000, 4096, PROT_READ) = 0
2619 mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5a49dab000
2619 mprotect(0x7f5a4a281000, 40960, PROT_READ) = 0
2619 mprotect(0x55d823827000, 4096, PROT_READ) = 0
2619 mprotect(0x7f5a4a2cf000, 4096, PROT_READ) = 0
2619 munmap(0x7f5a4a293000, 82054) = 0
2619 brk(NULL) = 0x55d8240b7000
2619 brk(0x55d8240d8000) = 0x55d8240d8000
2619 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0x4), ...}) = 0
2619 write(1, "Hello Test\n", 11) = 11
2619 mmap(NULL, 2101248, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f5a49baa000
2619 mlock(0x7f5a49baa010, 2097152) = -1 ENOMEM (Cannot allocate memory)
2619 write(1, "Locking memory failed: Cannot al"..., 46) = 46
2619 exit_group(0) = ?
2619 +++ exited with 0 +++

WSL logs:
wsl_log.zip

Expected behavior

mlock does function as expected, locking memory without failure.

Actual behavior

mlock always fails, returning -1.

[therealkenc]

On WSL2, it looks like the default max locked memory is 64kb. This is similar in spirit to #4575 but for locked memory instead of open files. On a stock Ubuntu on bare metal, the default limit is higher. The max locked memory can be increased with:

$ limit=8413752832
$ sudo prlimit --memlock=$limit:$limit --pid $$

[abpISCUE]

That did the trick, thank you :)

Remark: you have to add these lines to .bashrc to run program in eclipse; simply starting eclipse in a console after setting the memlock limit, does not suffice