[Bug 280318] fork() can deadlock on rtld_phdr_lock
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- Reply: bugzilla-noreply_a_freebsd.org: "[Bug 280318] fork() can deadlock on rtld_phdr_lock"
- Reply: bugzilla-noreply_a_freebsd.org: "[Bug 280318] fork() can deadlock on rtld_phdr_lock"
- Reply: bugzilla-noreply_a_freebsd.org: "[Bug 280318] fork() can deadlock on rtld_phdr_lock"
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Date: Tue, 16 Jul 2024 20:43:51 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=280318 Bug ID: 280318 Summary: fork() can deadlock on rtld_phdr_lock Product: Base System Version: 14.1-RELEASE Hardware: Any OS: Any Status: New Severity: Affects Only Me Priority: --- Component: threads Assignee: threads@FreeBSD.org Reporter: tavianator@tavianator.com I ran into a deadlock when calling fork() in a multi-threaded app with ASAN enabled. The backtrace looks like this: (gdb) bt #0 _umtx_op_err () at /usr/src/lib/libthr/arch/amd64/amd64/_umtx_op_err.S:38 #1 0x000000080054af50 in __thr_rwlock_wrlock (rwlock=rwlock@entry=0x80054f640, tsp=tsp@entry=0x0) at /usr/src/lib/libthr/thread/thr_umtx.c:324 #2 0x0000000800545571 in _thr_rwlock_wrlock (rwlock=<optimized out>, tsp=<optimized out>) at /usr/src/lib/libthr/thread/thr_umtx.h:239 #3 _thr_rtld_wlock_acquire (lock=0x80054f640) at /usr/src/lib/libthr/thread/thr_rtld.c:139 #4 0x000000080045ee49 in wlock_acquire (lock=0x80046bae0 <rtld_locks+32>, lockstate=<optimized out>) at /usr/src/libexec/rtld-elf/rtld_lock.c:275 #5 _rtld_atfork_pre (locks=locks@entry=0x7fffffffb290) at /usr/src/libexec/rtld-elf/rtld_lock.c:475 #6 0x000000080053e716 in thr_fork_impl (a=0x7fffffffb2f8) at /usr/src/lib/libthr/thread/thr_fork.c:194 #7 0x000000080053e658 in __thr_fork () at /usr/src/lib/libthr/thread/thr_fork.c:315 ... (gdb) thread 6 [Switching to thread 6 (LWP 154312 of process 84643)] (gdb) bt #0 __syscall () at __syscall.S:4 #1 0x0000000000311995 in __sanitizer::StaticSpinMutex::LockSlow (this=0x4af5b0 <__asan::instance+680>) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_mutex.cpp:24 #2 0x00000000002829b2 in __sanitizer::StaticSpinMutex::Lock (this=0x4af5b0 <__asan::instance+680>) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h:32 #3 __sanitizer::GenericScopedLock<__sanitizer::StaticSpinMutex>::GenericScopedLock (mu=0x4af5b0 <__asan::instance+680>, this=<optimized out>) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_mutex.h:383 #4 __sanitizer::LargeMmapAllocator<__asan::AsanMapUnmapCallback, __sanitizer::LargeMmapAllocatorPtrArrayDynamic, __sanitizer::LocalAddressSpaceView>::GetBlockBegin ( this=0x4af348 <__asan::instance+64>, ptr=0x802e4d120) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_allocator_secondary.h:184 #5 0x0000000000281666 in __sanitizer::CombinedAllocator<__sanitizer::SizeClassAllocator64<__asan::AP64<__sanitizer::LocalAddressSpaceView> >, __sanitizer::LargeMmapAllocatorPtrArrayDynamic>::GetBlockBegin (p=0x802e4d120, this=<optimized out>) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_allocator_combined.h:132 #6 __asan::Allocator::GetAsanChunkByAddr (this=<optimized out>, p=34408288544) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_allocator.cpp:824 #7 0x000000000027fbe3 in AllocationBegin (p=0x802e4d120) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_allocator.cpp:1215 #8 __sanitizer_get_allocated_begin (p=0x802e4d120) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_allocator.cpp:1256 #9 0x0000000000323f3f in __sanitizer::DTLS_on_tls_get_addr (arg_void=arg_void@entry=0x7fffdf7f89d0, res=res@entry=0x802e4d120, static_tls_begin=0, static_tls_end=0) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_tls_get_addr.cpp:138 #10 0x00000000002beb19 in ___interceptor___tls_get_addr (arg=0x7fffdf7f89d0) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_common_interceptors.inc:5426 #11 0x000000000031146c in __sanitizer::CollectStaticTlsBlocks (info=0x7fffdf7f8da8, size=<optimized out>, data=0x6) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:399 #12 0x0000000800458f4d in dl_iterate_phdr (callback=0x311430 <__sanitizer::CollectStaticTlsBlocks(dl_phdr_info*, unsigned long, void*)>, param=0x7fffdf7f8e38) at /usr/src/libexec/rtld-elf/rtld.c:4246 #13 0x00000000003107b2 in __sanitizer::GetStaticTlsBoundary (addr=<optimized out>, size=<optimized out>, align=<optimized out>) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:415 #14 __sanitizer::GetTls (addr=addr@entry=0x802e8a030, size=size@entry=0x7fffdf7f8ef0) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:526 #15 0x0000000000310b8b in __sanitizer::GetThreadStackAndTls (main=false, stk_addr=stk_addr@entry=0x802e8a010, stk_size=0x6, stk_size@entry=0x7fffdf7f8ef8, tls_addr=0x800701f2a <__syscall+10>, tls_addr@entry=0x802e8a030, tls_size=0x0, tls_size@entry=0x7fffdf7f8ef0) at /usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:610 #16 0x0000000000301ebe in __asan::AsanThread::SetThreadStackAndTls (this=this@entry=0x802e8a000, options=<optimized out>) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_thread.cpp:306 #17 0x0000000000301b5f in __asan::AsanThread::Init (this=0x802e8a000, options=options@entry=0x0) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_thread.cpp:253 #18 0x0000000000301fb7 in __asan::AsanThread::ThreadStart (this=0x14b, os_id=154312) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_thread.cpp:283 #19 0x00000000002f38b7 in asan_thread_start (arg=0x802e8a000) at /usr/src/contrib/llvm-project/compiler-rt/lib/asan/asan_interceptors.cpp:230 #20 0x000000080053db05 in thread_start (curthread=0x51b000001c80) at /usr/src/lib/libthr/thread/thr_create.c:289 #21 0x0000000000000000 in ?? () THread 1 is calling fork() which calls _rtld_atfork_pre() which acquires rtld_phdr_lock. Simultaneously, thread 6 is in the middle of dl_iterate_phdr() with rtld_phdr_lock held outside the loop. But the callback is apparently waiting for thread 1 to do something, which will never happen. It can be reproduced without ASAN too. Here's a somewhat artificial reproducer: $ cat foo.c #include <link.h> #include <pthread.h> #include <stdlib.h> #include <unistd.h> pthread_barrier_t in_callback, done_fork; int callback(struct dl_phdr_info *info, size_t size, void *data) { static int waited = 0; if (!waited) { pthread_barrier_wait(&in_callback); pthread_barrier_wait(&done_fork); waited = 1; } return 0; } void *start_routine(void *arg) { dl_iterate_phdr(callback, NULL); return NULL; } int main(void) { pthread_barrier_init(&in_callback, NULL, 2); pthread_barrier_init(&done_fork, NULL, 2); /* Create a thread to call dl_iterate_phdr() */ pthread_t thread; pthread_create(&thread, NULL, start_routine, NULL); /* Wait for the dl_iterate_phdr() callback to start */ pthread_barrier_wait(&in_callback); /* fork() will hang in _rtld_atfork_pre() */ pid_t pid = fork(); if (pid == 0) { return 0; } pthread_barrier_wait(&done_fork); pthread_join(thread, NULL); return 0; } $ cc -pthread foo.c -o foo $ ./foo That will hang until you kill the process. -- You are receiving this mail because: You are the assignee for the bug.