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[82.192.244.13]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324ea1aef7sm75936755f8f.7.2025.12.31.12.13.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 31 Dec 2025 12:13:59 -0800 (PST) Sender: Salvatore Bonaccorso Received: by eldamar.lan (Postfix, from userid 1000) id 8B3B7BE2DE0; Wed, 31 Dec 2025 21:13:58 +0100 (CET) Date: Wed, 31 Dec 2025 21:13:58 +0100 From: Salvatore Bonaccorso To: "Dylan E." Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org, gregkh@linuxfoundation.org, sashal@kernel.org, jjohnson@kernel.org Subject: Re: [BUG 6.18.2] Null Pointer Exception in Fair Scheduler Message-ID: References: <38b9cad8-1c17-4d89-9f17-44f89fb66ab8@candelatech.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <38b9cad8-1c17-4d89-9f17-44f89fb66ab8@candelatech.com> Hi Dylan, On Wed, Dec 31, 2025 at 12:00:07PM -0800, Dylan E. wrote: > Hello, > > When booting into the v6.18.2 tagged kernel from linux-stable, I get the > following > stack trace while booting into the system every 1 in 5 boots or so, usually > during > fsck or early systemd service initialization: > > --- > BUG: kernel NULL pointer dereference, address: 0000000000000051 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: Oops: 0000 [#1] SMP > CPU: 0 UID: 0 PID: 15 Comm: rcu_preempt Not tainted 6.18.2 #2 PREEMPT(full) > Hardware name:  /SKYBAY, BIOS 5.12 06/27/2017 > RIP: 0010:pick_task_fair+0x57/0x160 > Code: 66 90 66 90 48 8b 5d 50 48 85 db 74 10 48 8b 73 70 48 89 ef e8 3a 74 > ff ff 85 c0 75 71 be 01 00 00 00 48 89 ef e8 29 a5 ff ff <80> 78 51 00 48 89 > c3 0f 85 80 00 00 00 48 85 c0 0f 84 87 00 00 00 > RSP: 0000:ffffc900000d3cf8 EFLAGS: 00010086 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000800 > RDX: fffffc02295d3c00 RSI: 0000000000000800 RDI: 0000000002edc4f2 > RBP: ffff888108f13000 R08: 0000000000000400 R09: 0000000000000002 > R10: 0000000000000260 R11: ffff888108b74200 R12: ffff888265c2cd00 > R13: 0000000000000000 R14: ffff888265c2cd80 R15: ffffffff827c6fa0 > FS:  0000000000000000(0000) GS:ffff8882e2724000(0000) knlGS:0000000000000000 > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000051 CR3: 00000001110a5003 CR4: 00000000003706f0 > Call Trace: >   >  pick_next_task_fair+0x1d/0x3d0 >  __schedule+0x1ee/0x10c0 >  ? lock_timer_base+0x6d/0x90 >  ? rcu_gp_cleanup+0x560/0x560 >  schedule+0x23/0xc0 >  schedule_timeout+0x6e/0xe0 >  ? hrtimers_cpu_dying+0x1b0/0x1b0 >  rcu_gp_fqs_loop+0xfb/0x510 >  rcu_gp_kthread+0xcd/0x160 >  kthread+0xf5/0x1e0 >  ? kthreads_online_cpu+0x100/0x100 >  ? kthreads_online_cpu+0x100/0x100 >  ret_from_fork+0x114/0x140 >  ? kthreads_online_cpu+0x100/0x100 >  ret_from_fork_asm+0x11/0x20 >   > Modules linked in: i915 drm_buddy intel_gtt drm_client_lib > drm_display_helper drm_kms_helper igb cec dca rc_core i2c_algo_bit ttm > agpgart e1000e serio_raw hwmon drm mei_wdt i2c_core intel_oc_wdt video wmi > CR2: 0000000000000051 > ---[ end trace 0000000000000000 ]--- > RIP: 0010:pick_task_fair+0x57/0x160 > Code: 66 90 66 90 48 8b 5d 50 48 85 db 74 10 48 8b 73 70 48 89 ef e8 3a 74 > ff ff 85 c0 75 71 be 01 00 00 00 48 89 ef e8 29 a5 ff ff <80> 78 51 00 48 89 > c3 0f 85 80 00 00 00 48 85 c0 0f 84 87 00 00 00 > RSP: 0000:ffffc900000d3cf8 EFLAGS: 00010086 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000800 > RDX: fffffc02295d3c00 RSI: 0000000000000800 RDI: 0000000002edc4f2 > RBP: ffff888108f13000 R08: 0000000000000400 R09: 0000000000000002 > R10: 0000000000000260 R11: ffff888108b74200 R12: ffff888265c2cd00 > R13: 0000000000000000 R14: ffff888265c2cd80 R15: ffffffff827c6fa0 > FS:  0000000000000000(0000) GS:ffff8882e2724000(0000) knlGS:0000000000000000 > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 0000000000000051 CR3: 00000001110a5003 CR4: 00000000003706f0 > Kernel panic - not syncing: Fatal exception > Shutting down cpus with NMI > Kernel Offset: disabled > Rebooting in 30 seconds.. > --- > > I can't seem to reproduce this issue with the v6.18.1 tagged linux-stable > build, and > after bisecting between v6.18.1 and v6.18.2, I land on this commit (which is > clearly > not the problem): > > d911fa97dab3ba026a8b96bb7f833d007b7fc4e1 | wifi: ath12k: fix VHT MCS > assignment > > I don't have any ath12k radios in my system, but I do have 1 ath9k and 2 > ath10k > radios. A little up the tree I see this patch which *could* be related, but > I lack > the knowledge to know: > > b1497ea246396962156b63d5c568a16d6e32de0b | wifi: ath10k: move recovery check > logic into a new work > > Let me know if there's any more info that's needed or additional steps I can > take to > further diagnose the bug. This should be the same issue as reported in https://lore.kernel.org/oe-lkp/202510211205.1e0f5223-lkp@intel.com/ and then fixed in mainline with 127b90315ca0 ("sched/proxy: Yield the donor task") . Can you confirm picking this commit fixes the issue? Regards, Salvatore