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    Subjectblk_stop_queue/blk_start_queue confusion, problem, or bug???
    I've been trying to use the blk_start_queue and blk_stop_queue functions 
    in the network block device driver branch I'm working on. The stop works
    as expected, but the start doesn't. Processes that have tried to read or
    write to the device (after the queue was stopped) stay blocked in
    io_schedule instead of getting woken up (after blk_start_queue was
    called). Do I need to follow the call to blk_start_queue() with a call
    to wake_up() on the correct wait queues? Why not have that functionality
    be part of blk_start_queue()? Or was this an oversight/bug?

    The reason I'm using blk_stop_queue and blk_start_queue is to stop the
    request handling function (installed from blk_init_queue), from being
    re-invoked and to return when the network block device server goes down.
    That way, the driver doesn't need to block indefinately within the
    request handling function - which seems like it'd likely block other
    block drivers if it did this - and doesn't need to be handled by
    yet-another seperate kernel thread. Anyways... the stop is called from
    either the request handling function context or from an ioctl call
    context. If then a process tries to read or write to the device it
    blocks - just as I'd like (more like NFS behavior that way). When my
    code detects that the server has come back up again from the ioctl call
    context it calls blk_start_queue(). But the I/O blocked process stays

    Am I using these calls incorrectly or is something else going on?
    Insights, examples, very much appreciated.

    BTW: LKML has had a related thread on this some years ago in discussing
    how the block layer system handles request functions that must drop the
    spinlock and may block indefinately. That never seemed to get resolved
    though and makes me believe that's why Steven Whitehouse opted to use a
    multi-threaded approach to the NBD driver at one point.

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