Date: Tue, 23 Jul 2024 20:11:13 +0000 From: John F Carr <jfc@mit.edu> To: "mmel@freebsd.org" <mmel@freebsd.org> Cc: Konstantin Belousov <kib@freebsd.org>, Mark Millard <marklmi@yahoo.com>, FreeBSD Current <freebsd-current@freebsd.org>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org> Subject: Re: armv7-on-aarch64 stuck at urdlck Message-ID: <FABF7440-70D2-4BAB-8B0B-4CA950CFFA60@mit.edu> In-Reply-To: <6a969609-fa0e-419d-83d5-e4fcf0f6ec35@freebsd.org> References: <724db42b-5550-4381-8277-2971e6b3e8f1@freebsd.org> <B5E2275D-21F0-43C8-AF06-A45DB7448D66@yahoo.com> <86185657-e521-466b-89e2-f291aaac10a6@freebsd.org> <0EF18174-8735-46A4-BD71-FFA3472B319F@yahoo.com> <a1b978fe-ff54-4112-860c-b09500d89d0b@freebsd.org> <C0B42CBB-8F12-4597-A04B-26F2107E176E@yahoo.com> <33251aa3-681f-4d17-afe9-953490afeaf0@gmail.com> <0DD19771-3AAB-469E-981B-1203F1C28233@yahoo.com> <be023545-2b25-49ec-b6f1-9e05cd402646@gmail.com> <Zp95qtxK0CeDdp-d@kib.kiev.ua> <6a969609-fa0e-419d-83d5-e4fcf0f6ec35@freebsd.org>
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On Jul 23, 2024, at 13:46, Michal Meloun <meloun.michal@gmail.com> 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. > > > Michal > In this case (but not for all _aeabi_ functions) we can avoid division as long as page size is a power of 2. The function is static inline size_t round_up(size_t size) { if (size % _thr_page_size != 0) size = ((size / _thr_page_size) + 1) * _thr_page_size; return size; } The body can be condensed to return (size + _thr_page_size - 1) & ~(_thr_page_size - 1); This is shorter in both lines of code and instruction bytes. John Carrhelp
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