> You are right. I dont need to restore the signal handler - one system call > less in my signal handler. > I now saved a snapshot of the unfinished futex call. So I can experiment as > often as I want. > Poking a 1 does not work. But Poking a 0 works perfektly fine.
Thank you for this information. > And youre also right : I cannot use strace when the process is alredy > attached to my ptrace stuff. > So I will implement some PTRACE_SYSCALL steps myself to see the process > continuing after poking a 0. Yes that is the best way; big work too, cheers. > > Do you think, that errno could be the problem as well? Maybe a system call is > assinging a value to errno. Then the signal arrives and the handler tries to > access errno, too, which is blocked now? When we see that a syscall may be automatically restarted using the SA_RESTART flag in the struct sigaction (you may have to set this flag too if you plan to use sigaction(2) instead of signal(2)), then it may be safe to interrupt a syscall and the errno will be restored safely by the kernel when restarting the syscall. So, I do not believe it could be the problem for the kernel part. Il you choose not to use the SA_RESTART, your interrupted syscall may return -1 and have an EINTR errno. This could cause trouble in the user land depending on the code being executed. As I am no more accurate with this and the kernel stuff, you may consider my answer with lot of prudence. > If really the debug() call is the reason, I wonder why this problem does not > happen more often. I am debugging a lot in my code. And besides the debug > calls like every 2nd or 3rd code line ends up as a system call. If > interrupting a system call and executing another system call in the handler > should cause the problem, I feel like this kind of deadlock should happen > more often... I am not surprised by the non systematic circumstance because the debug() code may not be in totality re-entrant critical and you need to have your synchrone part of your program running debug() too to be in a re-entrant trouble. Just suppress the debug() call and test, you will have your answer. -- Futex hang when exiting using the window close button https://bugs.launchpad.net/bugs/57731 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
