Re: Strange Linux behaviour with blocking syscalls and stopsignals+SIGCONT

[Michael Kerrisk]

Hi Manfred,

> Michael Kerrisk wrote:
> 
> > c) The Linux baehviour has been arbitrary across kernel versions and 
> > system calls.  In particular, the following system calls showed this 
> > behaviour in earlier kernel versions, but then the behaviour was 
> > changed without forewarning and (AFAIK) without subsequent complaint:
> >
> > [snip]
> >
> >       * msgsnd() and msgrcv() in kernels before 2.6.9.
> >
> That was my change - and I even forgot to mention it in the changelog 
> (hiding in shame):
> I replaced -EINTR with -ERESTARTNOHAND.

Well, that change was useful for my argument: the change appears 
to have affected no-one, and so why not make it also for futex(), 
sigtimedwait(), semop()/semtimedop(), inotify read(),
epoll_wait()...

> That hides signals that are handled in the kernel from user space - 
> probably what we want.

Yes.

> Michael: Could you replace the EINTR in inotify.c with ERESTARTNOHAND? 
> That should prevent the kernel from showing the signal to user space.
> I'd guess that most instances of EINTR are wrong, except in device 
> drivers: It means we return from the syscall, even if the signal handler 
> wants to restart the system call.

I'll try patching a kernel to s/EINTR/ERESTARTNOHAND/ in relevant
places, and see how that goes.  If it goes well, I'll submit a 
patch.

Cheers,

Michael

-- 
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7 

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