• Jeff Layton's avatar
    pnfs: rework LAYOUTGET retry handling · 183d9e7b
    Jeff Layton authored
    There are several problems in the way a stateid is selected for a
    LAYOUTGET operation:
    
    We pick a stateid to use in the RPC prepare op, but that makes
    it difficult to serialize LAYOUTGETs that use the open stateid. That
    serialization is done in pnfs_update_layout, which occurs well before
    the rpc_prepare operation.
    
    Between those two events, the i_lock is dropped and reacquired.
    pnfs_update_layout can find that the list has lsegs in it and not do any
    serialization, but then later pnfs_choose_layoutget_stateid ends up
    choosing the open stateid.
    
    This patch changes the client to select the stateid to use in the
    LAYOUTGET earlier, when we're searching for a usable layout segment.
    This way we can do it all while holding the i_lock the first time, and
    ensure that we serialize any LAYOUTGET call that uses a non-layout
    stateid.
    
    This also means a rework of how LAYOUTGET replies are handled, as we
    must now get the latest stateid if we want to retransmit in response
    to a retryable error.
    
    Most of those errors boil down to the fact that the layout state has
    changed in some fashion. Thus, what we really want to do is to re-search
    for a layout when it fails with a retryable error, so that we can avoid
    reissuing the RPC at all if possible.
    
    While the LAYOUTGET RPC is async, the initiating thread always waits for
    it to complete, so it's effectively synchronous anyway. Currently, when
    we need to retry a LAYOUTGET because of an error, we drive that retry
    via the rpc state machine.
    
    This means that once the call has been submitted, it runs until it
    completes. So, we must move the error handling for this RPC out of the
    rpc_call_done operation and into the caller.
    
    In order to handle errors like NFS4ERR_DELAY properly, we must also
    pass a pointer to the sliding timeout, which is now moved to the stack
    in pnfs_update_layout.
    
    The complicating errors are -NFS4ERR_RECALLCONFLICT and
    -NFS4ERR_LAYOUTTRYLATER, as those involve a timeout after which we give
    up and return NULL back to the caller. So, there is some special
    handling for those errors to ensure that the layers driving the retries
    can handle that appropriately.
    Signed-off-by: 's avatarJeff Layton <jeff.layton@primarydata.com>
    Signed-off-by: 's avatarAnna Schumaker <Anna.Schumaker@Netapp.com>
    183d9e7b
errno.h 1.3 KB