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    SubjectRe: [PATCH v10 2/5] sched: CGroup tagging interface for core scheduling
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    On 2/23/21 4:05 AM, Peter Zijlstra wrote:
    > On Mon, Feb 22, 2021 at 11:00:37PM -0500, Chris Hyser wrote:
    >> On 1/22/21 8:17 PM, Joel Fernandes (Google) wrote:
    >> While trying to test the new prctl() code I'm working on, I ran into a bug I
    >> chased back into this v10 code. Under a fair amount of stress, when the
    >> function __sched_core_update_cookie() is ultimately called from
    >> sched_core_fork(), the system deadlocks or otherwise non-visibly crashes.
    >> I've not had much success figuring out why/what. I'm running with LOCKDEP on
    >> and seeing no complaints. Duplicating it only requires setting a cookie on a
    >> task and forking a bunch of threads ... all of which then want to update
    >> their cookie.
    >
    > Can you share the code and reproducer?

    Attached is a tarball with c code (source) and scripts. Just run ./setup_bug which will compile the source and start a
    bash with a cs cookie. Then run ./show_bug which dumps the cookie and then fires off some processes and threads. Note
    the cs_clone command is not doing any core sched prctls for this test (not needed and currently coded for a diff prctl
    interface). It just creates processes and threads. I see this hang almost instantly.

    Josh, I did verify that this occurs on Joel's coresched tree both with and w/o the kprot patch and that should exactly
    correspond to these patches.

    -chrish

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