Heavy usage of TLS causes stack overflow

[errangutan]

i wrote a dynamic library which uses tracing, which internally uses stds TLS implemention.
On unix, when I repeatedly load and then unload my library, eventually (after maybe 10 to 20 iterations) the program encounters a stack overflow.

After some research I found that this was due to the following flow:

pthread_key_create is called when TLS is initialized each time my library is loaded and my tracing logger is used.

pthread_key_delete is never called, there is no cleanup in this area.

Eventually pthread_key_create returns EAGAIN, which causes a panic.

Within the panic, the number of panics for the thread is tracked using TLS so when increase is called, we encounter a new panic (due to EAGAIN), which in turn will panic for the same reason.

We enter an endless loop of panics which eventually triggers a stack overflow.

[purplesyringa]

dlclose is fundamentally broken for this reason among others. musl, for example, makes dlclose a no-op. A stack overflow instead of an abort is something we can fix, but I'd advise you to avoid unloading and reloading libraries in runtime.

@rustbot label +A-thread-locals +A-panic +T-libs -needs-triage

[Noratrieb]

On unix, when I repeatedly load and then unload my library,

Yeah, std does not really support being dlclosed.