lkml.org 
[lkml]   [2005]   [May]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Scheduler: SIGSTOP on multi threaded processes
    On Wed, 4 May 2005, Olivier Croquette wrote:

    > Hello
    >
    > On a 2.6.11 x86 system, I am SIGSTOP'ing processes which have started
    > several threads before.
    >
    > As expected, all threads are suspended.
    >
    > But surprisingly, it can happen that some threads are still scheduled
    > after the SIGSTOP has been issued.
    >
    > Typically, they get scheduled 2 times within the next 5ms, before being
    > really stopped.
    >
    > Sadly, I could not reproduce that in a smaller example yet.
    >
    > As this behaviour is IMA against the SIGSTOP concept, I tried to analyze
    > the kernel code responsible for that. I could not really find the exact
    > lines.
    >
    > So here are my questions:
    >
    > 1. do you know any reason for which the SIGSTOP would not stop
    > immediatly all threads of a process?
    >
    > 2. where do the threads get suspended exactly in the kernel? I think it
    > is in signal.c but I am not sure exactly were.
    >
    > 3. can you confirm that the bug MUST be in my code? :)
    >
    > Thanks!
    >
    > Best regards
    >
    > Olivier


    The kernel doesn't do SIGSTOP or SIGCONT. Within init, there is
    a SIGSTOP and SIGCONT handler. These can be inherited by others
    unless changed, perhaps by a 'C' runtime library. Basically,
    the SIGSTOP handler executes pause() until the SIGCONT signal
    is received.

    Any delay in stopping is the time necessary for the signal to
    be delivered. It is possible that the section of code that
    contains the STOP/CONT handler was paged out and needs to be
    paged in before the signal can be delivered.

    You might quicken this up by installing your own handler for
    SIGSTOP and SIGCONT....

    static int stp;

    static void contsig(int sig) // SIGCONT handler
    {
    stp = 0;
    }

    static void stopsig(int sig) // SIGSTOP handler
    {
    stp = 1;
    while(stp)
    pause();
    }

    Put this near the code that will be executing most of the time.



    Cheers,
    Dick Johnson
    Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
    Notice : All mail here is now cached for review by Dictator Bush.
    98.36% of all statistics are fiction.
    -
    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: 2005-05-04 20:26    [W:0.027 / U:0.068 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site