On 23.07.2024 11:36, Konstantin Belousov wrote:
On Tue, Jul 23, 2024 at 09:53:41AM +0200, Michal Meloun wrote:
The good news is that I'm finally able to generate a working/locking
test case. The culprit (at least for me) is if "-mcpu" is used when
compiling libthr (e.g. indirectly injected via CPUTYPE in /etc/make.conf).
If it is not used, libthr is broken (regardless of -O level or debug/normal
build), but -mcpu=cortex-a15 will always produce a working libthr.
I think this is very significant progress.
Do you plan to drill down more to see what is going on?
So the problem is now clear, and I fear it may apply to other
architectures as well.
dlopen_object() (from rtld_elf),
https://cgit.freebsd.org/src/tree/libexec/rtld-elf/rtld.c#n3766,
holds the rtld_bind_lock write lock for almost the entire time a new
library is loaded.
If the code uses a yet unresolved symbol to load the library, the
rtl_bind() function attempts to get read lock of rtld_bind_lock and a
deadlock occurs.
In this case, it round_up() in _thr_stack_fix_protection,
https://cgit.freebsd.org/src/tree/lib/libthr/thread/thr_stack.c#n136.
Issued by __aeabi_uidiv (since not all armv7 processors support HW divide).
Unfortunately, I'm not sure how to fix it. The compiler can emit
__aeabi_<> in any place, and I'm not sure if it can resolve all the
symbols used by rtld_eld and libthr beforehand.
Michal
