[Bug 850] watchdog with delay of 1 failing to time out

[bugzilla-daemon at rtems.org]

http://www.rtems.org/bugzilla/show_bug.cgi?id=850


Joel Sherrill <joel.sherrill at oarcorp.com> changed:

           What    |Removed                     |Added
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             Status|ASSIGNED                    |CLOSED
    Attachment #238|text/x-patch                |text/plain
          mime type|                            |
 Attachment #238 is|0                           |1
              patch|                            |


A Watchdog (used to timeout an event) with a delay of 1 sometimes does not seem
to timeout.  The problem occurs, because for whatever reason when the watchdog
tickle function executes, the watchdog->delta_interval is 0. it is then
decremented before being tested, becomes huge and so doesnt time out.  It is
thought there is a race condition where the watchdog->delta_interval is
calculated by reference to a head (also with a delay of 1). But before it can
be added after the head, the head is removed, so the new head now has a delay
of 0.

Release:
RTEMS-4.6.5

Environment:
Linux Development Host (x86)
MPC862 (Freescale PowerPC) Target
Standard Rtems 4.6.5 Tool Distribution for PowerPC

How-To-Repeat:
I have no simple test code to repeat this.  The occurance is sporadic at best. 
Maybe 2 tasks waiting on events of a signle tick each, but in that case they
will probably become synchronised and so the race condition not occur.


--- Comment #1 from sjohnson at sakuraindustries.com  2005-12-12 00:50:55 ---
Fix:
Test watchdog->delta_interval for 0 before decrementing, to prevent decrementing 0 to 2^32-1.

--- Comment #2 from Joel Sherrill <joel.sherrill at oarcorp.com>  2006-03-07 16:11:00 ---
State-Changed-From-To: open->closed
State-Changed-Why: Patch applied to 4.6 branch and head.


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