Spawning threads in KVM/QEMU

Hi,

I've been experimenting with creating IO threads for the PV device drivers. Unfortunately, my experiments haven't gotten very far as QEMU tends to hang up a bit into booting the guest whenever I spawn a thread that does any sort of read/write on a file descriptor. My suspicion is that it has something to do with signals being delivered to the wrong thread but after masking out all the signals for this thread, I still had no luck.

Any clues to what may be going on?

Regards,

Anthony Liguori

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Quoted 8 lines · Anthony Liguori

I've been experimenting with creating IO threads for the PV device drivers. Unfortunately, my experiments haven't gotten very far as QEMU tends to hang up a bit into booting the guest whenever I spawn a thread that does any sort of read/write on a file descriptor. My suspicion is that it has something to do with signals being delivered to the wrong thread but after masking out all the signals for this thread, I still had no luck.

Maybe you set the mask too late? try setting it before creating the thread:
sigfillset(&thread_sig_mask); sigdelset(&thread_sig_mask,SIGILL); sigdelset(&thread_sig_mask,SIGFPE); sigdelset(&thread_sig_mask,SIGSEGV);

Quoted 11 lines · Dor Laor

Quoted 9 lines · Anthony Liguori

I've been experimenting with creating IO threads for the PV device drivers. Unfortunately, my experiments haven't gotten very far as QEMU tends to hang up a bit into booting the guest whenever I spawn a thread that does any sort of read/write on a file descriptor. My suspicion is that it has something to do with signals being delivered to the wrong thread but after masking out all the signals for this thread, I still had no luck.

Quoted 6 lines

Maybe you set the mask too late? try setting it before creating the thread:
sigfillset(&thread_sig_mask); sigdelset(&thread_sig_mask,SIGILL); sigdelset(&thread_sig_mask,SIGFPE); sigdelset(&thread_sig_mask,SIGSEGV);

When using RTC or HPET for timing you also need to mask SIGIO; you may also need to change F_SETOWN (enable_sigio_timer) with the correct thread id, i.e.:

fcntl(fd, F_SETOWN, gettid());

Luca

Quoted 12 lines · Anthony Liguori

Hi,

I've been experimenting with creating IO threads for the PV device drivers. Unfortunately, my experiments haven't gotten very far as QEMU tends to hang up a bit into booting the guest whenever I spawn a thread that does any sort of read/write on a file descriptor. My suspicion is that it has something to do with signals being delivered to the wrong thread but after masking out all the signals for this thread, I still had no luck.

Maybe you set the mask too late? try setting it before creating the thread:
sigfillset(&thread_sig_mask); sigdelset(&thread_sig_mask,SIGILL); sigdelset(&thread_sig_mask,SIGFPE); sigdelset(&thread_sig_mask,SIGSEGV); pthread_sigmask(SIG_SETMASK, &thread_sig_mask, &curr_sig_mask);

 if ((r = pthread_create(&thread_tid, NULL, thread_func, &init_data))) {
    ....

}
pthread_sigmask(SIG_SETMASK, &curr_sig_mask, NULL);