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Thu, 28 May 2026 00:21:29 -0700 (PDT) From: Ritesh Harjani (IBM) To: Venkat Rao Bagalkote , Peter Zijlstra , K Prateek Nayak , "Chen, Yu C" , tim.c.chen@linux.intel.com Cc: Madhavan Srinivasan , Shrikanth Hegde , Ritesh Harjani , "Christophe Leroy (CS GROUP)" , LKML , linuxppc-dev , linux-sched@vger.kernel.org Subject: Re: [BUG] sched/cache: "Make LLC id continuous" causes NULL cpumask dereference in build_sched_domains on POWER9 In-Reply-To: <51154de7-3700-4cb4-82f2-1b3a8fa427f7@linux.ibm.com> Date: Thu, 28 May 2026 12:24:39 +0530 Message-ID: References: <51154de7-3700-4cb4-82f2-1b3a8fa427f7@linux.ibm.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=utf-8 Content-Transfer-Encoding: 8bit Venkat Rao Bagalkote writes: > Greetings!!! > > I am seeing an early boot kernel panic due to NULL pointer dereference > on a POWER9 (pSeries) system when testing linux-next (next-20260522). > > > [    0.039029] NIP [c000000000e58504] _find_first_bit+0x44/0x130 > [    0.039043] LR [c000000000e58500] _find_first_bit+0x40/0x130 > [    0.039054] Call Trace: > [    0.039060] [c0000000090e7b80] [c00000000416af20] > schedutil_gov+0x0/0xa0 (unreliable) > [    0.039076] [c0000000090e7bc0] [c00000000038b3b8] > build_sched_domains+0xad8/0xe50 > [    0.039089] [c0000000090e7ce0] [c000000003045d78] > sched_init_smp+0xa8/0x164 > [    0.039102] [c0000000090e7d30] [c00000000300f374] > kernel_init_freeable+0x250/0x370 > [    0.039117] [c0000000090e7de0] [c000000000011f90] kernel_init+0x34/0x1e4 > [    0.039129] [c0000000090e7e50] [c00000000000debc] > ret_from_kernel_user_thread+0x14/0x1c > [    0.039142] ---- interrupt: 0 at 0x0 > [    0.039150] Code: 41820090 7c0802a6 393cffff fbe10038 7c7f1b78 > fba10028 fbc10030 3bc00000 793dd7e2 f8010050 4bae6e9d 60000000 > 2c290000 408200bc 283c0040 > [    0.039196] ---[ end trace 0000000000000000 ]--- > > Well, I am hitting this on 7.1.0-rc5-next-20260526-00010-gbfac43765a97 with Qemu Pseries TCG power10/11. [ 0.342868][ T1] smp: Bringing up secondary CPUs ... [ 0.342868][ T1] smp: Bringing up secondary CPUs ... [ 0.525419][ T1] smp: Brought up 1 node, 4 CPUs [ 0.525419][ T1] smp: Brought up 1 node, 4 CPUs [ 0.527992][ T1] numa: Node 0 CPUs: 0-3 [ 0.527992][ T1] numa: Node 0 CPUs: 0-3 [ 0.552787][ T1] BUG: Kernel NULL pointer dereference on read at 0x00000000 [ 0.552787][ T1] BUG: Kernel NULL pointer dereference on read at 0x00000000 [ 0.557446][ T1] Faulting instruction address: 0xc000000000fe3f1c [ 0.557446][ T1] Faulting instruction address: 0xc000000000fe3f1c cpu 0x0: Vector: 300 (Data Access) at [c000000006607800] pc: c000000000fe3f1c: _find_first_bit+0xc/0xc0 lr: c00000000027b7d8: build_sched_domains+0xbb4/0x1938 sp: c000000006607ac0 msr: 8000000002009033 dar: 0 dsisr: 80000 current = 0xc000000006f9fb00 paca = 0xc000000005670000 irqmask: 0x03 irq_happened: 0x09 pid = 1, comm = swapper/0 Linux version 7.1.0-rc5-next-20260526-00010-gbfac43765a97-dirty (powerpc64le-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40) #19 SMP PREEMPT Thu May 28 12:29:51 IST 2026 enter ? for help [link register ] c00000000027b7d8 build_sched_domains+0xbb4/0x1938 [c000000006607ac0] c00000000027b0a8 build_sched_domains+0x484/0x1938 (unreliable) [c000000006607c20] c000000004053180 sched_init_domains+0x114/0x1cc [c000000006607c70] c0000000040515e0 sched_init_smp+0x5c/0x17c [c000000006607cc0] c000000004012888 kernel_init_freeable+0x258/0x790 [c000000006607dc0] c000000000011f3c kernel_init+0x34/0x268 [c000000006607e30] c00000000000debc ret_from_kernel_user_thread+0x14/0x1c ---- Exception: 0 at 0000000000000000 -ritesh