On Fri, 9 Mar 2007 16:10:29 -0800 Luong Ngo wrote: > Thanks Parav, adding singal_allow(SIGALRM) wakeup the blocking > interruptible_sleep_on and checking the signal_pending would return > true now.
This means that there is also a bug in your userspace program - somehow when it invokes ioctl(), it has SIGALRM blocked. Use sigprocmask() (or pthread_sigmask() if your program is multithreaded) to ensure that SIGALRM is not blocked when you are expecting it to be processed. (Even if your program does not block SIGALRM, it may inherit a blocked SIGALRM from another program which have started it, so the safest way is to unblock SIGALRM explicitly.) Using allow_signal() is needed only if you create a kernel thread and want that thread to handle signals. > But a quick question is when detecting signal_pending, I > return -ERESTARTSYS, but the user process receive the return value of > ioctl call is -1, shouldn't it be -4 for EINTR? This is handled by syscall wrappers in libc - when the kernel returns an error code from a syscall, the syscall wrapper function puts the code into the per-thread errno variable and returns -1 to its caller. Your userspace code should check errno for the actual error code when it receives -1 from ioctl(). And the ERESTARTSYS error is really special - it never actually gets returned to the userspace program; instead, the syscall return code in the kernel catches it and either restarts the syscall after the signal handler completes, or converts the error code to EINTR; one of these actions is selected by the SA_RESTART flag to sigaction().
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