SQL SPID Blocking itself

I'm running SQL Server 2000.

I have a situation where users are timing out.

In enterprise manager I look at the locks/ProcessIDs.

I see

   spid 79开发者_StackOverflow社区 (Blocked By 79)

How is it possible for a session to block itself?

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This was introduced with Service pack 4 in SQL Server 2000. See this KB article: http://support.microsoft.com/kb/906344 for an explanation

When an SPID is waiting for an I/O page latch, you may notice that the blocked column briefly reports that the SPID is blocking itself. This behavior is a side effect of the way that latches are used for I/O operations on data pages