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    SubjectRe: another subtle signals issue
    On Tue, Feb 11, 2003 at 06:45:19PM -0800, Linus Torvalds wrote:
    > On Tue, 11 Feb 2003, Roland McGrath wrote:
    > >
    > > I think sys_semop would be closer to right if it used ERESTARTSYS instead
    > > of EINTR.
    > You probably mean ERESTARTSYSNOHAND.
    > There are lots of system calls that simply are not restartable. So
    > TIF_SIGPENDING in general should be set only if required, and not "because
    > it's easier".
    > > The reason I am concerned about this is that I think any case that is
    > > broken by the lack of the optimization in the patch below must also be
    > > broken vis a vis the semantics of stop signals and SIGCONT (when SIG_DFL,
    > > SIG_IGN, or blocked). POSIX says that when a process is stopped by
    > > e.g. SIGSTOP, and then continued by SIGCONT, any functions that were in
    > > progress at the time of stop are unaffected unless SIGCONT runs a handler.
    > > That is, nobody returns EINTR because of the stop/continue.
    > This is what ERESTARTNOHAND does, but quite often if you get interrupted
    > you have to return _partial_ results, which is quite inefficient and
    > sometimes breaks programs (ie you get things like a read() from a pipe
    > that returns a partial result because you resized the window, and a
    > SIGWINCH happened - and that is _bad_).
    > The old code tried rather hard to make signals that were truly ignored
    > (SIGSTOP/SIGCONT is not of that kind) be total non-events because of
    > things like this.

    For things with a timeout, shouldn't they be converted to use
    ERESTART_RESTARTBLOCK? The situation Roland is describing is just
    about the same as the original problem with nanosleep.

    Daniel Jacobowitz
    MontaVista Software Debian GNU/Linux Developer
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