stable rustc --version hangs forever

[fuchsnj]

starting with nightly-2018-11-04 and anything later, just checking the version or doing anything with rustc causes the process to hang forever. It seems like it is waiting on a lock (no CPU usage)

Stable rust works fine, and well as any nightly version before this one.

OS is Ubuntu 18.04.1 LTS
Rust stable/nightly versions were installed with rustup

nathan@nathan-Precision-7510:~$ rustc +nightly-2018-11-04 --version
^C
nathan@nathan-Precision-7510:~$ rustc +nightly-2018-11-03 --version
rustc 1.32.0-nightly (8b096314a 2018-11-02)

The last few lines from strace rustc +nightly-2018-11-04 --version are

...
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
readlink("/etc/malloc.conf", 0x7ffd8dd4a900, 4096) = -1 ENOENT (No such file or directory)
open("/proc/sys/vm/overcommit_memory", O_RDONLY) = 3
futex(0x7fbdfd2510c8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
futex(0x7fbdfe014228, FUTEX_WAIT_PRIVATE, 2, NULL

It hangs on the FUTEX_WAIT call forever

[ehuss]

Another user reported the same issue here: rust-lang/cargo#6384

That is the first release that removed jemalloc. I would suspect that is related, but I don't have any ideas on how to reproduce.

[fuchsnj]

Here is a stacktrace of the stuck process
https://gist.github.com/fuchsnj/5612923e3613a915b65aece0dd920149

This was captured with gdb on a stuck process running rustc +nightly --version
I just updated my nightly version, so it should be running the latest. (Couldn't really tell you which version that was though...)

[ehuss]

Do you have ESET antivirus installed (or any other security software)?

I installed ESET and I'm able to reproduce it. It looks like jemalloc is getting stuck recursively trying to initialize itself.

@alexcrichton My guess is that there is something about jemalloc 5 has changed how it initializes maybe?

[fuchsnj]

Yes, I have ESET antivirus installed.

[alexcrichton]

cc @gnzlbg, do you know if jemalloc has a fix for this perhaps?

[ehuss]

It appears to be an issue with ESET, jemalloc 5, and rustc being built for an old kernel.

It looks like jemalloc 5 has started to use CLOEXEC. Since rust is built with a very old linux kernel, it has to use fcntl (here) instead of just passing O_CLOEXEC (which requires 2.6.23). fcntl is intercepted by ESET which attempts to find the open symbol with dlsym. dlsym requires calling calloc, which hangs since jemalloc is in the middle of initializing.

I have confirmed building rustc locally (with jemalloc) that it does not hang, presumably because it is using O_CLOEXEC.

I don't offhand see any workarounds (other than using a newer kernel).

[gnzlbg]

I don't offhand see any workarounds (other than using a newer kernel).

The PR that started using CLOEXEC was jemalloc/jemalloc#872 which fixed jemalloc/jemalloc#528 . We could patch jemalloc to not use CLOEXEC when built for Rust, but... it looks to me that jemalloc is doing the right thing here, and that this is a corner case that should be handled in ESETs side.

We should open a bug with ESET about their jemalloc 5 / fcntl / Rust support, maybe they can roll a fix quickly. Depending on their timeline, patching jemalloc to not use CLOEXEC shouldn't be hard: when will the first stable Rust version with this issue land? I think we should consider it a regression.

[alexcrichton]

Opening a bug (if we can) with ESET sounds good to me for now, but if that doesn't pan out we can probably work around this and just not use cloexec there as it's a short-lived fd anyway

[pnkfelix]

Something I think deserves clarification here: as of PR #55238 (resolving issue #36963), builds of rustc stopped linking in jemalloc by default; however, if I am correctly reading the documentation and commit messages of that PR, the rustc built via CI opts back into having jemalloc linked to rustc (on Linux or Mac OS X). (and thus the nightly you get via rustup or otherwise downloading CI-built executables will link to jemalloc).

Its a pretty confusing situation, IMO, since attempts to locally replicate the behavior described here via a local build of rustc would need to turn that flag back on. (I think @ehuss is saying in their comment above that they took care to opt back into jemalloc in their local build. But it is easily overlooked.)

(Also: the CI's opting back into using jemalloc affects not just the nightly builds but also the beta and stable ones......? I'm a bit flummoxed as to why we would want the out-of-the-box local build to differ in this way from what we deploy. At the very least I would expect more prominent documentation as to how to properly recreate the CI's build.)

[gnzlbg]

the rustc built via CI opts back into having jemalloc linked to rustc.

IIUC the intent was for rustc to always depend on jemalloc by default, since that was the status-quo before that change, but to allow people to build it without jemalloc, e.g., if they want to use it in a system where jemalloc is not available. It might be that this did not fully materialize.

[pnkfelix]

Yes, I too thought that was the intent. But...:

rust/config.toml.example

Lines 399 to 401 in f4b07e0

	# Link the compiler against `jemalloc`, where on Linux and OSX it should
	# override the default allocator for rustc and LLVM.
	#jemalloc = false

---

It could very well be that I am wrong about my expectations, and that if one wants to replicate the CI build product, one should take care to actually run configure with args taken from e.g.:

rust/.travis.yml

Line 33 in f4b07e0

RUST_CONFIGURE_ARGS="--enable-extended --enable-profiler --enable-lldb --set rust.jemalloc"

(or with configure args taken from https://github.com/rust-lang/rust/blob/master/appveyor.yml, as appropriate to one's platform)

[pnkfelix]

I'm just going to open a separate issue about this discrepancy between the CI vs local builds, rather than continuing to clutter up this issue's comment thread. Sorry for the noise!