fatal runtime error: assertion failed: output.write(&bytes).is_ok()

[dpc]

So I was recompiling a typescript nextjs project in a nix derivation, that previously worked (Nix builds are kind of reproducible, so that's very unexpected) and it failed with a weird error:

guardian-ui> @fedimint/types:build: cache miss, executing a873a14720ccc5d2
guardian-ui>  WARNING  passwd database shell="/noshell" which is not executable (ENOENT: No such file or directory), falling back to /bin/sh
guardian-ui> @fedimint/types:build: fatal runtime error: assertion failed: output.write(&bytes).is_ok()
guardian-ui> @fedimint/types:build:
guardian-ui>  Tasks:    0 successful, 1 total
guardian-ui> Cached:    0 cached, 1 total
guardian-ui>   Time:    1.095s

I suspect my kernel version might be different because I just upgraded to NixOS 24.05 recently.

I traced this panic to

rust/library/std/src/sys/pal/unix/process/process_unix.rs

Line 125 in 1689a5a

rtassert!(output.write(&bytes).is_ok());

I got a strace output:

guardian-ui> [pid   675] setsid()                    = 675
guardian-ui> [pid   675] ioctl(0, TIOCSCTTY, 0)      = 0
guardian-ui> [pid   675] open("/dev/fd", O_RDONLY|O_LARGEFILE|O_CLOEXEC|O_DIRECTORY) = 17
guardian-ui> [pid   675] fcntl(17, F_SETFD, FD_CLOEXEC) = 0
guardian-ui> [pid   675] getdents64(17, 0x7ffff7b2f4b8 /* 22 entries */, 2048) = 528
guardian-ui> [pid   675] getdents64(17, 0x7ffff7b2f4b8 /* 0 entries */, 2048) = 0
guardian-ui> [pid   675] close(5)                    = 0                                                                                   (6 results) 20:25:45 [2127/32726]
guardian-ui> [pid   675] close(6)                    = 0
guardian-ui> [pid   675] close(7)                    = 0
guardian-ui> [pid   675] close(8)                    = 0
guardian-ui> [pid   675] close(9)                    = 0
guardian-ui> [pid   675] close(10)                   = 0
guardian-ui> [pid   675] close(11)                   = 0
guardian-ui> [pid   675] close(12)                   = 0
guardian-ui> [pid   675] close(13)                   = 0
guardian-ui> [pid   675] close(14)                   = 0
guardian-ui> [pid   675] close(15)                   = 0
guardian-ui> [pid   675] close(16)                   = 0
guardian-ui> [pid   675] close(17)                   = -1 EBADF (Bad file descriptor)
guardian-ui> [pid   675] close(18)                   = 0
guardian-ui> [pid   601] <... recvfrom resumed>"", 8, 0, NULL, NULL) = 0
guardian-ui> [pid   675] close(24 <unfinished ...>
guardian-ui> [pid   601] close(17 <unfinished ...>
guardian-ui> [pid   675] <... close resumed>)        = 0
guardian-ui> [pid   675] execve("/build/yarn--1717471544555-0.05173506673993855/yarn", ["/build/yarn--1717471544555-0.051"..., "run", "build"], 0x7ffff7e5b1a0 /* 135 vars *
/ <unfinished ...>
guardian-ui> [pid   601] <... close resumed>)        = 0
guardian-ui> [pid   675] <... execve resumed>)       = -1 ETXTBSY (Text file busy)
guardian-ui> [pid   675] write(18, "\0\0\0\32NOEX", 8) = -1 EBADF (Bad file descriptor)
guardian-ui> [pid   675] write(2, "fatal runtime error: assertion f"..., 68) = 68
guardian-ui> [pid   675] rt_sigprocmask(SIG_BLOCK, ~[RTMIN RT_1 RT_2], [], 8) = 0
guardian-ui> [pid   675] tkill(675, SIGABRT)         = 0
guardian-ui> [pid   675] rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
guardian-ui> [pid   675] --- SIGABRT {si_signo=SIGABRT, si_code=SI_TKILL, si_pid=675, si_uid=1000} ---
guardian-ui> [pid   601] close(14)                   = 0
guardian-ui> [pid   601] close(15)                   = 0
guardian-ui> [pid   601] close(16)                   = 0
guardian-ui> [pid   601] fcntl(11, F_DUPFD_CLOEXEC, 0) = 14
guardian-ui> [pid   601] fcntl(14, F_SETFD, FD_CLOEXEC) = 0
guardian-ui> [pid   601] fcntl(11, F_DUPFD_CLOEXEC, 0) = 15
guardian-ui> [pid   601] fcntl(15, F_SETFD, FD_CLOEXEC) = 0

I'm not sure where to even report it, and a bit tired to dig deeper. Creating the issue just for reference.

The whole thing can be reproduced with:

nix build 'github:fedimint/ui?rev=1fc0cc6322f4ebb0f0854cd870b79c9971ff4b34#guardian-ui'

I'm going to try it on some machines and see when it fails and when works.

[dpc]

On a machine with Ubuntu and nix I had around with Linux 5.15.0-101-generic, this works. On my two systems with new NixOS and Linux 6.9.2 it fails.

[dpc]

I have verified that downgrading to linux kernel 6.8.11 makes the problem go away.

[tbu-]

Nix builds are kind of reproducible, so that's very unexpected

Nix does not take kernel version into account in its reproducibility guarantees.

[dpc]

Yes, everything else is locked in place (kind of). That's why I immediately suspected the kernel might be a problem.

So to sum up: something about very recent linux kernel version is breaking some assumptions in Rust standard code w.r.t forking/execing, which leads to this internal panic. It's hard for me to tell is it a kernel regression, or Rust's stdlib assumptions were incorrect, or maybe I'm missing something else entirely.

I am happening to witness it because I'm running as recent kernel version as NixOS can provide trying to avoid some bcachefs bugs. With time the problem might become more widespread.

[workingjubilee]

Ah, a relatively small diff, then! Should be easy to find the offending commit. torvalds/linux@f610c35...c8eef17

[dpc]

🤔 , dozens of rebuild + reboot cycles... . I'll see if I can find a time to do it. No promises. :D