On Tue, Jul 23, 2024 at 07:46:51PM +0200, Michal Meloun wrote: > > > 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.
This is a common issue, we pre-resolve a lot of symbols to avoid lock recursion. Please take a look at lib/libthr/thread/thr_rtld.c _thr_rtld_init().
