Deadlocked on the same resource (same index)

I'm seeing a deadlock issue that traces out the following 1204 report
below. You can see that one process is granted a shared lock (Mode: S)
on the index and another process is granted an exclusive lock on the
same index.
How is that possible? What scenarios could lead to this? I know that
deadlocks can happen over the same resource when one or two processes
are trying to raise the isolation level, but that doesn't seem to be
the case here.
It almost seems like the two processes are requesting locks (that they
already have?) and waiting for the other to release. What scenarios
could lead to this?
Unfortunately I can't show any code. Here is the trace file:
Michael Swart
Wait-for graph
Node:1
KEY: 7:2133582639:3 (180223bc5cb5) CleanCnt:1 Mode: X Flags: 0x0
Grant List 3::
Owner:0x52e00720 Mode: X Flg:0x0 Ref:0 Life:02000000 SPID:98
ECID:0
SPID: 98 ECID: 0 Statement Type: UPDATE Line #: 34
Input Buf: RPC Event: sp_executesql;1
Requested By:
ResType:LockOwner Stype:'OR' Mode: S SPID:93 ECID:0 Ec0x7C1615D8)
Value:0x52dd7340 Cost0/0)
Node:2
KEY: 7:2133582639:3 (a80172417f28) CleanCnt:1 Mode: S Flags: 0x0
Grant List 0::
Owner:0x52e2e7c0 Mode: S Flg:0x0 Ref:0 Life:00000001 SPID:93
ECID:0
SPID: 93 ECID: 0 Statement Type: INSERT Line #: 2
Input Buf: Language Event: EXEC LoadDataPartitions
Requested By:
ResType:LockOwner Stype:'OR' Mode: X SPID:98 ECID:0 Ec0x5A2E5578)
Value:0x52fa6780 Cost0/1129C)
Victim Resource Owner:
ResType:LockOwner Stype:'OR' Mode: S SPID:93 ECID:0 Ec0x7C1615D8)
Value:0x52dd7340 Cost0/0)
Michael Swart wrote:
> I'm seeing a deadlock issue that traces out the following 1204 report
> below. You can see that one process is granted a shared lock (Mode: S)
> on the index and another process is granted an exclusive lock on the
> same index.
> How is that possible? What scenarios could lead to this? I know that
> deadlocks can happen over the same resource when one or two processes
> are trying to raise the isolation level, but that doesn't seem to be
> the case here.
The "classic" deadlock scenario is where two processes try to acquire
locks on two resources in different order.

> It almost seems like the two processes are requesting locks (that they
> already have?) and waiting for the other to release. What scenarios
> could lead to this?
Different order of table accesses within two transactions for example.

> Unfortunately I can't show any code. Here is the trace file:
> Michael Swart
<snip/>
Unfortunately I'm no expert at trace file reading. But you can try to
catch the deadlock with Enterprise Manager. Then you can directly see SQL
statements that lead to the deadlock. HTH.
Kind regards
robert