• Dan Williams's avatar
    scsi: async sd resume · 3c31b52f
    Dan Williams authored
    async_schedule() sd resume work to allow disks and other devices to
    resume in parallel.
    This moves the entirety of scsi_device resume to an async context to
    ensure that scsi_device_resume() remains ordered with respect to the
    completion of the start/stop command.  For the duration of the resume,
    new command submissions (that do not originate from the scsi-core) will
    be deferred (BLKPREP_DEFER).
    It adds a new ASYNC_DOMAIN_EXCLUSIVE(scsi_sd_pm_domain) as a container
    of these operations.  Like scsi_sd_probe_domain it is flushed at
    sd_remove() time to ensure async ops do not continue past the
    end-of-life of the sdev.  The implementation explicitly refrains from
    reusing scsi_sd_probe_domain directly for this purpose as it is flushed
    at the end of dpm_resume(), potentially defeating some of the benefit.
    Given sdevs are quiesced it is permissible for these resume operations
    to bleed past the async_synchronize_full() calls made by the driver
    We defer the resolution of which pm callback to call until
    scsi_dev_type_{suspend|resume} time and guarantee that the callback
    parameter is never NULL.  With this in place the type of resume
    operation is encoded in the async function identifier.
    There is a concern that async resume could trigger PSU overload.  In the
    enterprise, storage enclosures enforce staggered spin-up regardless of
    what the kernel does making async scanning safe by default.  Outside of
    that context a user can disable asynchronous scanning via a kernel
    command line or CONFIG_SCSI_SCAN_ASYNC.  Honor that setting when
    deciding whether to do resume asynchronously.
    Inspired by Todd's analysis and initial proposal [2]:
    Cc: Len Brown <len.brown@intel.com>
    Cc: Phillip Susi <psusi@ubuntu.com>
    [alan: bug fix and clean up suggestion]
    Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
    Suggested-by: default avatarTodd Brandt <todd.e.brandt@linux.intel.com>
    [djbw: kick all resume work to the async queue]
    Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
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