https://bugs.kde.org/show_bug.cgi?id=498936
--- Comment #1 from Tavian Barnes <taviana...@gmail.com> ---
Okay here's a more reduced testcase:
```
#include <pthread.h>
#include <stdatomic.h>
atomic_bool start, stop;
void *work(void *ptr) {
start = 1;
while (!stop);
return NULL;
}
int main(void) {
pthread_t thread;
pthread_create(&thread, NULL, work, NULL);
while (!start);
stop = 1;
pthread_join(thread, NULL);
return 0;
}
```
When I run this with valgrind, it hangs. Running GDB on valgrind itself, it
seems like the new thread is blocked on acquiring a lock:
(gdb) bt
#0 0x000000005801e839 in vgMemCheck_helperc_LOADV8 (a=1097769) at
/usr/src/debug/valgrind/valgrind-3.24.0/memcheck/mc_main.c:5637
#1 0x0000001002e8d7d9 in ?? ()
#2 0x0000001002da9e80 in ?? ()
#3 0x0000000059a98040 in ?? ()
#4 0x0000000059a98038 in vgPlain_brk_limit ()
#5 0x0000000000000000 in ?? ()
(gdb) thread 2
[Switching to thread 2 (LWP 2026357)]
#0 0x00000000580010e2 in do_syscall_WRK ()
(gdb) bt
#0 0x00000000580010e2 in do_syscall_WRK ()
#1 0x000000005804d1b8 in vgPlain_do_syscall (a7=0, a8=0, sysno=0,
a1=<optimized out>, a2=<optimized out>, a3=<optimized out>, a4=0, a5=0, a6=0)
at ../coregrind/m_syscall.c:1183
#2 vgPlain_read (fd=<optimized out>, buf=<optimized out>, count=<optimized
out>) at ../coregrind/m_libcfile.c:338
#3 0x00000000580d3914 in vgModuleLocal_sema_down (as_LL=0 '\000',
sema=0x10020063f0) at ../coregrind/m_scheduler/sema.c:107
#4 acquire_sched_lock (p=0x10020063f0) at
../coregrind/m_scheduler/sched-lock-generic.c:69
#5 0x0000000058099d77 in vgModuleLocal_acquire_sched_lock (p=<optimized out>)
at ../coregrind/m_scheduler/sched-lock.c:88
#6 vgPlain_acquire_BigLock_LL (who=0x0) at
../coregrind/m_scheduler/scheduler.c:422
#7 vgPlain_acquire_BigLock (tid=2, who=0x5827ec58 "thread_wrapper(starting new
thread)") at ../coregrind/m_scheduler/scheduler.c:346
#8 0x00000000580db229 in thread_wrapper (tidW=2) at
../coregrind/m_syswrap/syswrap-linux.c:83
#9 run_a_thread_NORETURN (tidW=2) at
../coregrind/m_syswrap/syswrap-linux.c:155
#10 0x00000000580db6bf in vgModuleLocal_start_thread_NORETURN (arg=<optimized
out>) at ../coregrind/m_syswrap/syswrap-linux.c:329
#11 0x0000000058001181 in do_syscall_clone_amd64_linux ()
#12 0xdeadbeefdeadbeef in ?? ()
#13 0xdeadbeefdeadbeef in ?? ()
#14 0xdeadbeefdeadbeef in ?? ()
#15 0xdeadbeefdeadbeef in ?? ()
#16 0x0000000000000000 in ?? ()
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