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    SubjectRe: BLKSECDISCARD ioctl and hung tasks
    On Wed, Feb 19, 2020 at 09:54:31AM -0800, Salman Qazi wrote:
    > On Tue, Feb 18, 2020 at 6:55 PM Ming Lei <ming.lei@redhat.com> wrote:
    > >
    > > On Tue, Feb 18, 2020 at 08:11:53AM -0800, Jesse Barnes wrote:
    > > > On Fri, Feb 14, 2020 at 7:47 PM Ming Lei <ming.lei@redhat.com> wrote:
    > > > > What are the 'other operations'? Are they block IOs?
    > > > >
    > > > > If yes, that is why I suggest to fix submit_bio_wait(), which should cover
    > > > > most of sync bio submission.
    > > > >
    > > > > Anyway, the fix is simple & generic enough, I'd plan to post a formal
    > > > > patch if no one figures out better doable approaches.
    > > >
    > > > Yeah I think any block I/O operation that occurs after the
    > > > BLKSECDISCARD is submitted will also potentially be affected by the
    > > > hung task timeouts, and I think your patch will address that. My only
    > > > concern with it is that it might hide some other I/O "hangs" that are
    > > > due to device misbehavior instead. Yes driver and device timeouts
    > > > should generally catch those, but with this in place we might miss a
    > > > few bugs.
    > > >
    > > > Given the nature of these types of storage devices though, I think
    > > > that's a minor issue and not worth blocking the patch on, given that
    > > > it should prevent a lot of false positive hang reports as Salman
    > > > demonstrated.
    > >
    > > Hello Jesse and Salman,
    > >
    > > One more question about this issue, do you enable BLK_WBT on your test
    > > kernel?
    >
    > It doesn't exist on the original 4.4-based kernel where we reproduced
    > this bug. I am curious how this interacts with this bug.

    blk-wbt can throttle discard request and keep discard queue not too
    deep.

    However, given block erase is involved in BLKSECDISCARD, I guess blk-wbt
    may not avoid this task hung issue completely.


    Thanks,
    Ming

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