lkml.org 
[lkml]   [2003]   [Feb]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    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
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 13:33    [W:0.022 / U:0.216 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site