I used locking for all the reads and writes to cpl when the problem initialy
surfaced. Interestingly the problem was the same after locking was used.
Like I said, the problem either occured during context switch, or during the
normal execution of a single thread.
----- Original Message -----
From: "Rokicki, Andrew" <ARokicki@xxxxxxxxxxxxx>
To: <redhat-devel-list@xxxxxxxxxx>
Cc: "'Ming Lei'" <lei.ming@xxxxxxxxx>
Sent: Tuesday, May 06, 2003 5:31 AM
Subject: RE: can linux RT thread corrupt global variable?
> I am not an expert on this.
> As a test try using a mutex to protect cpl from thread switching during
> modification.
>
> //somewhere on top of your program.
> static pthread_mutex_t mtxThread = PTHREAD_MUTEX_INITIALIZER;
> ....
> ...
> //in you threads.
> pthread_mutex_lock(&mtxThread);
> cpl=1234 //however you are modifying it.
> pthread_mutex_unlock(&mtxThread);
> ......
>
>
> On Monday, May 05, 2003 8:40 PM, Ming Lei [SMTP:lei.ming@xxxxxxxxx] wrote:
> > Platform:
> > Intel Pentium II; RedHat 7.2 with kernel version 2.4.7-10, libc 2.2.4-13
> and
> > gcc 2.96.
> >
> > Problem description:
> >
> > a program has a thread of priority 12, a thread of priority 10, a thread
> of
> > priority 6, and the main process at priority 0. All the threads except
> main
> > process is created with pthread_create, and defined SCHED_FIFO as real
> time
> > scheduler policy.
> >
> > There is a global variable I define as 'int cpl'. All the threads and
main
> > process may alter cpl at any time. cpl may have one of these values {0,
> > 0xf000006e, 0xf0000068, 0xe0000000, 0xe0000060}.
> >
> > <Problem=> at some point of execution which cpl should be a value say
> > e0000060, but the actual value retained at cpl is another say e0000000;
> that
> > is, the value is changed without the program actually done anything on
it.
> > The retained value I observed is kind of historic value(one of these
value
> > in the above set), not the arbituary value. The problem had occured just
> > after context switch, also occured during a thread execution.
> >
> > <Confirm> I used Intel debug register to track any writing to the cpl
> memory
> > address globally, which is the way GDB use for x86 hardware watchpoint
> > implementation. I could see all the writing from my program to change
cpl,
> > but failed to see the source from which the problem occured. So I dont
> know
> > what cause the problem.
> >
> > Can anyone listening give me a direction or hint on this annoying
> situation?
> > Any help is thanked here.
> >
> > PS. please cc to this email address.
> > -Ming
> >
> >
> > Related questions:
> >
> > Is linux kernel 2.4.10 considered strictly preemptive such as VxWorks or
> > other RTOS? I guess 2.4.10 may simulate preemptive with running
scheduler
> on
> > every syscall or interrupt returns. Am I right?
> >
> > Is printf() real-time priority thread safe?
> >
> >
> >
> > _______________________________________________
> > Redhat-devel-list mailing list
> > Redhat-devel-list@xxxxxxxxxx
> > https://listman.redhat.com/mailman/listinfo/redhat-devel-list
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