HEAD r252840 (illumos bug 3836) and our TRIM are incompatible, causing deadlocks

[Steven Hartland]

----- Original Message ----- 
From: "Alexander Motin" <mav at FreeBSD.org>
...
>>> It disables r252840 when ZFS TRIM is enabled (vfs.zfs.trim.enabled=1).
>>> When TRIM is disabled, patch enables direct free execution from
>>> r252840 and removes ZIO_STAGE_VDEV_IO_START and
>>> ZIO_STAGE_VDEV_IO_ASSESS stages from the pipeline.
>>
>> I assume you removed the vdev stages when trim is disabled as an
>> optimization, due to the fact that a free wouldn't result in any
>> physical IO?
> 
> As I have written above, zio_vdev_io_start() called on top level takes 
> SCL_ZIO, that causes described deadlock. That is why I needed to block 
> those stages, useless in that case any way, just at the entrance point. 
> I've decided it will be more effective to remove whole stages then add 
> checks inside.

Thanks for the clarification, I'll continue testing :)

    Regards
    Steve

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