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    SubjectRe: Q. drm/i915 shrinker, synchronize_rcu_expedited() from handlers
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    On ti, 2017-05-09 at 20:04 -0700, Hugh Dickins wrote:
    > On Mon, 8 May 2017, Joonas Lahtinen wrote:
    > > On pe, 2017-05-05 at 14:57 -0700, Hugh Dickins wrote:
    > > > On Fri, 5 May 2017, Joonas Lahtinen wrote:
    > > > > On ma, 2017-05-01 at 11:05 +0900, J. R. Okajima wrote:
    > > > > > Thanx for the reply.
    > > > > > 
    > > > > > Andrea Arcangeli:
    > > > > > > 
    > > > > > > Yes I already reported this, my original fix was way more efficient
    > > > > > > (and also safer considering the above) than what landed upstream. My
    > > > > > > feedback was ignored though.
    > > > > > > 
    > > > > > > https://lists.freedesktop.org/archives/intel-gfx/2017-April/125414.html
    > > > > > 
    > > > > > I see.
    > > > > > Actually on my test system for v4.11-rc8, kthreadd, kworker, kswapd and
    > > > > > others all stopped working due to the synchronize_rcu_expedited call
    > > > > > from i915_gem_shrinker_count. It is definitly a show stopper for me as
    > > > > > an i915 user.
    > > > > 
    > > > > Filing a bug in freedesktop.org with all the details is the fastest way
    > > > > of getting help. Without the bug (and with such little information as
    > > > > the previous e-mail) it's hard to estimate the extent and nature of the
    > > > > bug.
    > > > > 
    > > > > I've anyway gone and prepared a patch to drop the RCU sync completely
    > > > > from shrinker phase, as discussed originally with Chris.
    > > > 
    > > > Is that a patch that will be suitable for 4.11-stable?  Please do post
    > > > it here.  I had not experienced this i915-induced hang at all when
    > > > Andrea first mentioned it, nor even on 4.11-rc8; but now with 4.11
    > > > final I can get it fairly easily (I haven't tried Andrea's fix yet).
    > > 
    > > Please try:
    > > 
    > > https://patchwork.freedesktop.org/patch/154713/
    > > 
    > > If it works, a Tested-by: would be appreciated.
    >
    > Yes, that works for me, thank you.
    >
    > Tested-by: Hugh Dickins <hughd@google.com>
    >
    > But the linked patch seems to be lacking a Reported-by (not me) tag,
    > a Fixes tag, a Cc stable tag, and any indication in the Subject or
    > commit message that this patch is something needed to fix hangs
    > observed by several people - it just sounds like a minor cleanup.

    It is a patch that was agreed to be pushed anyway, so if it wouldn't
    have resolved the problem, I'd have pushed it as is.

    I'll add J. R. Okajima as Reported-by and refer to the bisected commit,
    even though so far Freedesktop Bugzilla or intel-gfx mailing list has
    no other reports.

    Regards, Joonas
    -- 
    Joonas Lahtinen
    Open Source Technology Center
    Intel Corporation

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