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| 2 | * Copyright (c) 2024 Alexey Dobriyan <[email protected]>
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| 3 | *
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| 4 | * Permission to use, copy, modify, and distribute this software for any
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| 5 | * purpose with or without fee is hereby granted, provided that the above
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| 6 | * copyright notice and this permission notice appear in all copies.
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| 7 | *
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| 8 | * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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| 9 | * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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| 10 | * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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| 11 | * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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| 12 | * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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| 13 | * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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| 14 | * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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| 15 |
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| 16 |
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| 17 | #undef NDEBUG
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| 18 | #include <assert.h>
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| 19 | #include <errno.h>
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| 20 | #include <fcntl.h>
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| 21 | #include <string.h>
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| 22 | #include <unistd.h>
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| 23 |
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| 24 | int main(void)
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| 25 | {
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| 26 | |
| 27 | * The following solutions don't really work:
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| 28 | *
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| 29 | * 1) jit kernel module which creates kernel thread:
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| 30 | * test becomes arch-specific,
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| 31 | * problems with mandatory module signing,
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| 32 | * problems with lockdown mode,
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| 33 | * doesn't work with CONFIG_MODULES=n at all,
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| 34 | * kthread creation API is formally unstable internal kernel API,
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| 35 | * need a mechanism to report test kernel thread's PID back,
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| 36 | *
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| 37 | * 2) ksoftirqd/0 and kswapd0 look like stable enough kernel threads,
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| 38 | * but their PIDs are unstable.
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| 39 | *
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| 40 | * Check against kthreadd which always seem to exist under pid 2.
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| 41 |
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| 42 | int fd = open("/proc/2/status", O_RDONLY);
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| 43 | assert(fd >= 0);
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| 44 |
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| 45 | char buf[4096];
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| 46 | ssize_t rv = read(fd, buf, sizeof(buf));
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| 47 | assert(0 <= rv && rv < sizeof(buf));
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| 48 | buf[rv] = '\0';
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| 49 |
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| 50 | assert(strstr(buf, "Kthread:\t1\n"));
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| 51 |
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| 52 | return 0;
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| 53 | }
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