OpenAFS Master Repository branch, master, updated. openafs-devel-1_5_76-3167-gf401993

[Gerrit Code Review]

The following commit has been merged in the master branch:
commit f40199327a8753d8350b5fefedc2bb556b8b00a6
Author: Simon Wilkinson <sxw@your-file-system.com>
Date:   Thu Nov 22 08:41:51 2012 +0000

    rx: Return success value when cancelling an event
    
    When cancelling an event that holds reference counts, we need
    to know whether the attempt to cancel the event was successful
    or not, otherwise references can be double put when the
    cancellation races with the event firing. Take the follwing
    
    Thread A			Event Thread
    =========			============
    
    				... event fired ...
    MUTEX_ENTER(&obj->lock);
    if (obj->event) {
        rxevent_Cancel(&obj->event);
        obj_put(&obj->refcnt);
    }
    MUTEX_EXIT(&obj->lock)
    				MUTEX_ENTER(&obj->lock);
    				if (event == obj->event)
    				    rxevent_Put(&obj->event);
    				...
    				MUTEX_EXIT(&obj->lock);
    				obj_put(&obj->refcnt);
    
    Holding obj->lock doesn't control whether the event is fired or
    not. Only putting the reference if the event being fired matches
    that in obj doesn't help - it just leaks a reference in a different
    race.
    
    So, make rxevent_Cancel return true if it did actually cancel the
    event, and false if the event has already been fired. This means
    that Thread A can become
    
    MUTEX_ENTER(&obj->lock);
    if (rxevent_Cancel(&obj->event)
        obj_put(&obj->refcnt);
    MUTEX_EXIT(&obj->lock)
    
    In the example above, rxevent_Cancel would return false.
    
    Change-Id: I48e012774c97c9d9588b00687428a32795be2b37
    Reviewed-on: http://gerrit.openafs.org/8539
    Tested-by: BuildBot <buildbot@rampaginggeek.com>
    Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
    Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>

 src/rx/rx_event.c      |   15 +++++++++++++--
 src/rx/rx_event.h      |    2 +-
 src/rx/rx_prototypes.h |    1 -
 3 files changed, 14 insertions(+), 4 deletions(-)

-- 
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