Jörg Walter wrote:
> Hi!
>
> I have found a bug where qemu would sit in an endless loop whenever "-smb"
> was
> enabled and accessed. It is probably the same problem some people in the user
> forums talk about, and here's my analysis and fix:
>
> On glibc systems with NPTL, fork() is not atomic with regard to signals,
> while
> on non-NPTL-systems, it is. This behaviour is considered to be correct by the
> libc developers, as no relevant spec forbids this behaviour.
>
> See this thread for details:
> http://sourceware.org/ml/libc-hacker/2007-02/msg00009.html
>
> In qemu, accessing the SMB ip-address causes the slirp code to issue a fork
> in
> slirp/misc.c, which hangs, as we are in mid-emulation and SIGALARM signals
> come in at a high rate, probably triggering the above mentioned behaviour.
>
> This patch solves the problem by temporarily blocking all signals until the
> fork is over. It doesn't unblock signals in the child, as I assume that
> executing the server program will care for that anyways. It works for me,
> finally I can access "-smb"-folders again.
>
> --
> CU
> Jörg
> --- slirp/misc.c 2007-08-27 10:30:20.000000000 +0200
> +++ slirp/misc.c.new 2007-08-27 10:29:50.000000000 +0200
> @@ -313,6 +313,7 @@
> int opt;
> int master;
> char *argv[256];
> + int mask;
> #if 0
> char buff[256];
> #endif
> @@ -346,8 +347,10 @@
> }
> }
>
> + mask = sigsetmask(~0);
> switch(fork()) {
> case -1:
> + sigsetmask(mask);
> lprint("Error: fork failed: %s\n", strerror(errno));
> close(s);
> if (do_pty == 2)
> @@ -426,6 +429,7 @@
> exit(1);
>
> default:
> + sigsetmask(mask);
> if (do_pty == 2) {
> close(s);
> so->s = master;
Could you rewrite this using pthread_sigmask, to make it thread safe?
Thiemo
