Signal mask restore anomaly

[Hendricks, Kevin]

Hi,

This bug was fixed in 2.2.14pre9 and later kernels.  Please upgrade or diff
/arch/ppc/kernel/signal.c to see the fix.

Kevin




At 00:05 -0400 8/17/00, Jeffrey Hawkins wrote:
>Frank,
>
>I am able to reproduce the same failures on a 2.2.13
>PPC Kernel, with GCC 2.95.3-2c and GLIBC 2.1.3-15d.
>Ran same test code on Solaris with correct operation.
>
>The failure is definitely a MASK restoration problem.
>Since, one can recover from the problem by UNBLOCKING
>the SIGINT.
>
>I believe the problem may be an interaction between the
>Terminal I/O related SIGNALS being used (SIGTSTP and
>SIGINT) and the use of the STDIO Library calls (printf
>and getch).  By replacing the SIGTSTP and SIGINT signals
>with SIGUSR1 and SIGUSR2, everything worked correctly
>(tested via "kill" command from a separate terminal
>window).
>
>Looking at the GLIBC Bug Database, I didn't see any bugs
>which seem to correspond to this failure mechanism.  Most
>of the SIGNALS bugs seem to be related THREADS.
>
>Looks like it is time submit a bug report to GNU....
>
>Jeff
>
>
>Frank Jas wrote:
>>
>> Under certain circumstances, a signal blocked while a
>> signal handler is executing will not be restored.
>>
>> This is my kernel info:
>>
>> Linux 2.2.6-15apmac #1 Mon May 31 03:54:09 EDT 1999 ppc unknown
>>
>> The behavior does not occur under Intel versions (2.2.5-15smp).
>>
>> Below is a program that tests out the use of signal masks
>> with sigaction().  It sets up a handler for SIGINT and
>> SIGTSTP.  The handler for SIGTSTP adds SIGINT to
>> the signal mask for that handler.  So while the SIGTSTP
>> handler is executing, occurences of SIGINT will be
>> blocked until the handler returns.  SIGTSTP will also
>> be blocked.
>>
>> #define _POSIX_SOURCE 1
>> #define _GNU_SOURCE 1
>>
>> #include <signal.h>
>> #include <errno.h>
>> #include <stdio.h>
>>
>> void on_intr (signum)
>>         int signum ;
>> {
>>         printf("\n    Interrupted with signal %d. \n", signum) ;
>> }
>>
>> void on_tstp (signum)
>>         int signum;
>> {
>>         printf ("\n     Handler for SIGTSTP wants text or ^C or ^Z: ") ;
>>         getchar () ;
>> }
>>
>> void main ()
>> {
>>         struct sigaction  new_intr_action;
>>         struct sigaction  new_tstp_action;
>>         int    c ;
>>
>>         sigemptyset (&new_intr_action.sa_mask);
>>         new_intr_action.sa_handler = on_intr;
>>         new_intr_action.sa_flags   = SA_RESTART;
>>
>>         sigaction  (SIGINT, &new_intr_action, 0);
>>
>>         sigemptyset (&new_tstp_action.sa_mask);
>>         sigaddset   (&new_tstp_action.sa_mask, SIGINT);
>>         new_tstp_action.sa_handler = on_tstp;
>>         new_tstp_action.sa_flags   = SA_RESTART;
>>
>>         sigaction  (SIGTSTP, &new_tstp_action, 0);
>>
>>         printf("Starting main input loop enter text or ^Z or ^C:\n") ;
>>
>>         while ((c = getchar ()) != EOF) {
>>                 putchar (c);
>>         }
>> }
>>
>> The following execution sequence leads to the anomalous behavior.
>>
>> Trigger the SIGTSTP handler with a ^Z
>> While executing the handler, deliver a ^Z and ^C
>> Hit return to return from the handler.
>> Another instance of the SIGTSTP handler should execute.
>> Hit return to return from that instance of the handler.
>> Notice that the SIGINT handler does not execute and should have.
>> Any subsequent SIGINT are apparently blocked.
>>
>> Apparently the nested occurence of SIGTSTP effected the restore
>> of the SIGINT mask, and the handling of the pending SIGINT.
>>
>> The same behavior will result using 'kill' from another window
>> to send the signals.
>>
>> Please let me know if this is not the appropriate venue for this
>> post.
>>
>> Frank Jas
>>
>
>--
>********************************************************
>
>Jeffrey Hawkins
>
>Senior Staff Software Engineer
>Motorola Wireless Data Solutions Engineering
>
>Address: DEPT:  DQ525
>         MS:    IL-02-1055A
>         1301 East Algonquin Road
>         Schaumburg, IL 60196
>
>Phone:   (847)576-7463
>FAX:     (847)576-7737
>
>********************************************************
>


--
Kevin B. Hendricks, Associate Professor of Operations and Information
Technology
Richard Ivey School of Business, University of Western Ontario
London, Ontario  N6A-3K7  CANADA
khendricks at ivey.uwo.ca, (519) 661-3874, fax: 519-661-3959


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