From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2AF1D35FF68; Wed, 28 Jan 2026 13:56:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769608615; cv=none; b=HgU8yb9ze59+wnCIMethfzXyzYQn9TedWk+Unft5P0DQ/472mKghsObunQs9xY2m1dVUFX2oDjfFLk57zVXFBWMPN1MPoXKHLy4yPR+hP4Tny/sYgQ12VxVgC/ovfUhiUX3/tu2Jc/bI3TnVuq8l+atsspi0FHlVtKVfG1Fo3RQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769608615; c=relaxed/simple; bh=gmQ5tFpfhM0FBX1l+SJSMl+GseRfiifShHW6tOR4FFo=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=BOKyApV417TrlC6ppVyQISzA57XDMoDO2DSNoIiHfxMYFuMSDdtUUaz1VqiZboBPhMtREoeAA5ikDT7cp12hVeixKkBNuInkhni0m2SG7A846fkQV6glKOg50cNHYWGv2CE81OQPmFIOrImAIc9LKcYQYc1qqJj64YkDZKUEpuo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JEu8SXMl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="JEu8SXMl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 69F68C4CEF7; Wed, 28 Jan 2026 13:56:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769608615; bh=gmQ5tFpfhM0FBX1l+SJSMl+GseRfiifShHW6tOR4FFo=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=JEu8SXMlxPgwC/nUeHc1pBON7D2YloibI7NwXoNqFJK/U0b6A7VKSMEQsq0wxCMn8 sYSgGky+M69nLIU8MvaXQ3ddSnIiN6c2bQJ9R3kTO5PHUhIAE9d/xLUe8Tz/PaqcQh 4McscJKNehIztn74b6KojxS5S7E9FzELRnVxZC+Bw3TCx/ubuI0/DzHPAcpO9cdiiK 732kLEyua/0Ms7UB0ku3BsTyt7Dr99ffydrw3WG7/0YHLdQGLm08xTmptv5bRSw2qJ X3Cto3v++a3Qz8rGZzIIf2qcLUuJAOG9NDD0RAP7DNkv69q9s4TBdNhbu2wCLCDuMi Q6RFDL/uik7BA== From: Thomas Gleixner To: Shrikanth Hegde , Peter Zijlstra , Ihor Solodrai , LKML Cc: Gabriele Monaco , Mathieu Desnoyers , Michael Jeanson , Jens Axboe , "Paul E. McKenney" , "Gautham R. Shenoy" , Florian Weimer , Tim Chen , Yury Norov , bpf , sched-ext@lists.linux.dev, Kernel Team , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Puranjay Mohan , Tejun Heo Subject: Re: [patch V5 00/20] sched: Rewrite MM CID management In-Reply-To: References: <20251119171016.815482037@linutronix.de> <2b7463d7-0f58-4e34-9775-6e2115cfb971@linux.dev> <877bt29cgv.ffs@tglx> Date: Wed, 28 Jan 2026 14:56:51 +0100 Message-ID: <87y0lh96xo.ffs@tglx> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Wed, Jan 28 2026 at 18:28, Shrikanth Hegde wrote: > On 1/28/26 5:27 PM, Thomas Gleixner wrote: > watchdog: CPU 23 self-detected hard LOCKUP @ mm_get_cid+0xe8/0x188 > watchdog: CPU 23 TB:1434903268401795, last heartbeat TB:1434897252302837 (11750ms ago) > NIP [c0000000001b7134] mm_get_cid+0xe8/0x188 > LR [c0000000001b7154] mm_get_cid+0x108/0x188 > Call Trace: > [c000000004c37db0] [c000000001145d84] cpuidle_enter_state+0xf8/0x6a4 (unreliable) > [c000000004c37e00] [c0000000001b95ac] mm_cid_switch_to+0x3c4/0x52c > [c000000004c37e60] [c000000001147264] __schedule+0x47c/0x700 So if the above spins in mm_get_cid() then the below is just a consequence. > watchdog: CPU 11 self-detected hard LOCKUP @ plpar_hcall_norets_notrace+0x18/0x2c > watchdog: CPU 11 TB:1434903340004919, last heartbeat TB:1434897249749892 (11895ms ago) > NIP [c0000000000f84fc] plpar_hcall_norets_notrace+0x18/0x2c > LR [c000000001152588] queued_spin_lock_slowpath+0xd88/0x15d0 > Call Trace: > [c00000056b69fb10] [c00000056b69fba0] 0xc00000056b69fba0 (unreliable) > [c00000056b69fc30] [c000000001153ce0] _raw_spin_lock+0x80/0xa0 > [c00000056b69fc50] [c0000000001b9a34] raw_spin_rq_lock_nested+0x3c/0xf8 > [c00000056b69fc80] [c0000000001b9bb8] mm_cid_fixup_cpus_to_tasks+0xc8/0x28c > [c00000056b69fd00] [c0000000001bff34] sched_mm_cid_exit+0x108/0x22c > [c00000056b69fd40] [c000000000167b08] do_exit+0xf4/0x5d0 > [c00000056b69fdf0] [c00000000016800c] make_task_dead+0x0/0x178 > [c00000056b69fe10] [c0000000000316c8] system_call_exception+0x128/0x390 > [c00000056b69fe50] [c00000000000cedc] system_call_vectored_common+0x15c/0x2ec > I am wondering if it this loop in mm_get_cid, which may not be getting a cid > for a long time? Is that possible? It shouldn't be possible by design, but it seems there is a corner case lurking somewhere which hasn't been covered. Let me stare at the logic in the transition functions once more. That's where CPU11 comes from: > [c00000056b69fc80] [c0000000001b9bb8] mm_cid_fixup_cpus_to_tasks+0xc8/0x28c The exiting it initiated a transition back from per CPU to per task mode and that seems to make things unhappy for mysterious reasons. Thanks, tglx