Hi Russell,
Russell King - ARM Linux linux@arm.linux.org.uk wrote on 09/02/2011 07:48:12 PM:
On Fri, Sep 02, 2011 at 07:40:34PM +0200, Ulrich Weigand wrote:
Russell King - ARM Linux linux@arm.linux.org.uk wrote on 09/02/2011 07:22:59 PM:
On Fri, Sep 02, 2011 at 04:47:35PM +0200, Ulrich Weigand wrote:
Assume the scenario you initally describe, where a first signal is ignored and leads to system call restart. With your latest patch, you call into syscall_restart which sets everything up to restart the call (with interrupts disabled).
I don't think SIG_IGN signals even set the TIF work flag, so they never even cause a call into do_signal(). Therefore, as far as syscalls go, attempting to send a process (eg) a SIGINT which its handler is set to SIG_IGN results in the process not even being notified about the attempt - we won't even wake up while the syscall is sleeping.
I don't see why SIG_IGN signals shouldn't set the TIF work flag; the decision whether to ignore a signal is only made once we've got to get_signal_to_deliver.
Yes, having looked deeper, you seem to be right - but only if the thread is being ptraced. If it's not being ptraced, ignored signals don't make it that far.
And yes, we can end up processing the interrupt before the SVC is executed, which is still a hole. So we need to avoid doing the restart in userspace - which might actually make things easier. I'll take a look into that over the weekend.
After some more discussions with Uli I've now created a patch that hopefully will address the issue on s390. The new code always uses the TIF_RESTART_SVC work flag to restart the system call if there is no signal to deliver. Only if there is a signal to deliver the traditional rewind of the instruction pointer is used to restart the system call (for -ERESTARTNOINTR and -ERESTARTSYS with a SA_RESTART signal handler).
In case you are interested in the code is available at git://git390.marist.edu/pub/scm/linux-2.6.git features in particular git commit 4a6a001c39ac196530d8378408b61d6d2fee70d9.
blue skies, Martin