minor grammar #1
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XrXr
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Dec 10, 2024
I got a SEGV core dump with the stack trace as follows:
#0 __pthread_kill_implementation (no_tid=0, signo=14, threadid=0) at ./nptl/pthread_kill.c:50
tmm1#1 __pthread_kill_internal (signo=14, threadid=0) at ./nptl/pthread_kill.c:78
tmm1#2 __GI___pthread_kill (threadid=0, signo=14) at ./nptl/pthread_kill.c:89
tmm1#3 <signal handler called> () at /lib/x86_64-linux-gnu/libc.so.6
tmm1#4 stackprof_start (argc=<optimized out>, argv=<optimized out>, self=<optimized out>) at stackprof.c:228
tmm1#5 vm_call_cfunc_with_frame_
...
Notice that `threadid=0` in the top frame -- the SEGV comes from inside
libc as it tries to dereference `threadid`.
The signal comes from stackprof's signal handler:
if (pthread_self() != _stackprof.target_thread) {
pthread_kill(_stackprof.target_thread, sig);
return;
}
During stackprof_start(), `_stackprof.target_thread` is 0.
You can recreate the stack trace in the crash with a program that does
`pthread_kill(0, SIGALRM)`:
#include <signal.h>
int
main(void)
{
pthread_kill(0, SIGALRM);
}
Only set `running` after target_thread is set to avoid this crash in
case the timer expires after `settimer()` but before setting
`target_thread`.
Also, since the ordering is important here, make `running`
`volatile sig_atomic_t` to prevent the compiler from doing unwanted
reordering.
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