[win-pv-devel] lost SRB in xenvbd

[Andreas Kinzler <ml-ak@xxxxxxxxx>]

After days of debugging I find that xenvbd is causing hangs no matter if 
Xen 4.8.0, 4.7.1 or 4.5.1. In any case I see PdoResets
XENVBD|__PdoReset:Target[1] ====>
XENVBD|PdoReset:Target[1] ====> (Irql=2)
XENVBD|__PdoPauseDataPath:Target[1] : Waiting for 0 Submitted requests
XENVBD|__PdoPauseDataPath:Target[1] : 0/0 Submitted requests left (0 
iterrations)
XENVBD|PdoReset:Target[1] <==== (Irql=2)
XENVBD|__PdoReset:Target[1] <====

The MSDN doc says a PDO reset is triggered if a SRB times out. In any 
hang I always see the following line:
XENVBD: FDO: Srbs            : 1 / 254 (12166611 Total)

From what I read in the driver source code this means that there is one 
SRB pending. But nothing is in the queues, rings, ... (see below). I 
assume that SRB has been lost somewhere?
Any help greatly appreciated.

BTW: Disabling discard caused the hang to appear quite rapidly (only one 
debug pass so far)
Regards Andreas

XENVBD: LOOKASIDE: REQUESTs: 0 / 83 (0 failed)
XENVBD: LOOKASIDE: SEGMENTs: 0 / 888 (0 failed)
XENVBD: LOOKASIDE: INDIRECTs: 0 / 0 (0 failed)
XENVBD: QUEUE: Fresh     : 0 / 33
XENVBD: QUEUE: Prepared  : 0 / 51
XENVBD: QUEUE: Submitted : 0 / 36
XENVBD: QUEUE: Shutdown  : 0 / 0
XENVBD: FRONTEND: TargetId=1 DeviceId=832 BackendId=0
XENVBD: FRONTEND: FrontendPath device/vbd/832
XENVBD: FRONTEND: BackendPath  /local/domain/0/backend/vbd/2/832
XENVBD: FRONTEND: TargetPath   data/scsi/target/1
XENVBD: FRONTEND: State   : ENABLED
XENVBD: FRONTEND: Caps    : CONNECTED
XENVBD: FRONTEND: Features: PERSISTENT
XENVBD: FRONTEND: DiskInfo: 100000000 @ 512 (512) 00000000
XENVBD: GRANTER: CONNECTED ENABLED
XENVBD: GRANTER: 1 / 889
XENVBD: BLOCKRING: Requests  : 65968184 / 65968184
XENVBD: BLOCKRING: SharedRing : 0xFFFFD001935A9000
XENVBD: BLOCKRING: SharedRing : 65974354 / 65974355 - 65974354 / 65974355
XENVBD: BLOCKRING: FrontRing  : 65974354 / 65974354 (32)
XENVBD: BLOCKRING: Order      : 0
XENVBD: BLOCKRING: Grants[0 ] : 0xFFFFE001E17B7B88 (33)
XENVBD: NOTIFIER: Int / DPC : 56337743 / 64634483
XENVBD: NOTIFIER: Channel : FFFFE001E17A76D0 (10)



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