Re: [PATCH v10 2/5] sched: CGroup tagging interface for core scheduling

From: Chris Hyser <chris.hyser@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
	Nishanth Aravamudan <naravamudan@digitalocean.com>,
	Julien Desfossez <jdesfossez@digitalocean.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Vineeth Pillai <viremana@linux.microsoft.com>,
	Aaron Lu <aaron.lwe@gmail.com>,
	Aubrey Li <aubrey.intel@gmail.com>,
	tglx@linutronix.de, linux-kernel@vger.kernel.org,
	mingo@kernel.org, torvalds@linux-foundation.org,
	fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
	Phil Auld <pauld@redhat.com>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	vineeth@bitbyteword.org, Chen Yu <yu.c.chen@intel.com>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Agata Gruza <agata.gruza@intel.com>,
	Antonio Gomez Iglesias <antonio.gomez.iglesias@intel.com>,
	graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com,
	pjt@google.com, rostedt@goodmis.org, derkling@google.com,
	benbjiang@tencent.com,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	James.Bottomley@hansenpartnership.com, OWeisse@umich.edu,
	Dhaval Giani <dhaval.giani@oracle.com>,
	Junaid Shahid <junaids@google.com>,
	jsbarnes@google.com, Ben Segall <bsegall@google.com>,
	Josh Don <joshdon@google.com>, Hao Luo <haoluo@google.com>,
	Tom Lendacky <thomas.lendacky@amd.com>
Subject: Re: [PATCH v10 2/5] sched: CGroup tagging interface for core scheduling
Date: Tue, 23 Feb 2021 14:25:16 -0500	[thread overview]
Message-ID: <e1ee6187-77a7-dbf2-3e14-adba48460f5b@oracle.com> (raw)
In-Reply-To: <YDTFWZPdmrDuYd91@hirez.programming.kicks-ass.net>

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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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