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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 26 Sep 2024 14:32:09.4278 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 02134bca-be00-4fee-8170-08dcde380103 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: AM3PEPF00009B9D.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB8343 On 9/26/24 13:42, Vishal Chourasia wrote: > I've noticed a kernel panic consistently occurring on the mainline v6.11 > kernel (see attached dmesg log below). > > The panic occurs almost every time I build the Linux kernel from source. > > Steps to Reproduce: > > make clean > ./scripts/config -e LOCALVERSION_AUTO > ./scripts/config --set-str LOCALVERSION -master-with-print > make localmodconfig > make -j8 -s vmlinux modules > >>>From my investigation, it seems that the function pick_eevdf() can return NULL. > Commit f12e1488 ("sched/fair: Prepare pick_next_task() for delayed dequeue") > introduces an access on the return value of pick_eevdf(). If 'se' was NULL, > it can lead to a null pointer dereference. > > # objdump -S vmlinux | grep -C 5 c0000000001cfebc > c0000000001cfeb0: 00 00 00 60 nop > struct sched_entity *se = pick_eevdf(cfs_rq); > c0000000001cfeb4: 78 f3 c3 7f mr r3,r30 > c0000000001cfeb8: 01 46 ff 4b bl c0000000001c44b8 > if (se->sched_delayed) { > c0000000001cfebc: 51 00 23 89 lbz r9,81(r3) <<<<<< > struct sched_entity *se = pick_eevdf(cfs_rq); > c0000000001cfec0: 78 1b 7f 7c mr r31,r3 > if (se->sched_delayed) { > c0000000001cfec4: 00 00 09 2c cmpwi r9,0 > c0000000001cfec8: 98 00 82 40 bne c0000000001cff60 > > r3 is NULL which can be verified from the register context shared in the > dmesg logs > > Here is the state of my git repository: > # git log --oneline > 684a64bf32b6 (HEAD -> master, origin/master, origin/HEAD) Merge tag 'nfs-for-6.12-1' of git://git.linux-nfs.org/projects/anna/linux-nfs > f7fccaa77271 Merge tag 'fuse-update-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse > 4165cee7ecb1 Merge tag 'exfat-for-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/linkinjeon/exfat > 79952bdcbcea Merge tag 'f2fs-for-6.12-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs > fa8380a06bd0 Merge tag 'bpf-next-6.12-struct-fd' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next > 68e5c7d4cefb Merge tag 'kbuild-v6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/masahiroy/linux-kbuild > 7f8de2bf0725 Merge tag 'linux-cpupower-6.12-rc1-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux > cd3d64772981 Merge tag 'i3c/for-6.12' of git://git.kernel.org/pub/scm/linux/kernel/git/i3c/linux > > > To determine why pick_eevdf() would return NULL, I added a few printk statements > Based on one of the printk logs in the shared dmesg log, it appears that if > pick_eevdf() is called for a 'cfs_rq' whose 'cfs_rq->curr' is NULL and there > are no eligible entities on that 'cfs_rq', it will return NULL. > > # git diff > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 225b31aaee55..8c5b96f1cd49 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -48,6 +48,7 @@ > #include > #include > #include > +#include > > #include > > @@ -907,16 +908,25 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq) > static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq) > { > struct rb_node *node = cfs_rq->tasks_timeline.rb_root.rb_node; > + struct rb_node *tmpnode = node; > struct sched_entity *se = __pick_first_entity(cfs_rq); > + struct sched_entity *tmpse = se; > struct sched_entity *curr = cfs_rq->curr; > + struct sched_entity *tmpcurr = curr; > struct sched_entity *best = NULL; > - > + struct sched_entity *tmp = NULL; > /* > * We can safely skip eligibility check if there is only one entity > * in this cfs_rq, saving some cycles. > */ > - if (cfs_rq->nr_running == 1) > - return curr && curr->on_rq ? curr : se; > + if (cfs_rq->nr_running == 1) { > + tmp = curr && curr->on_rq ? curr : se; > + if (!tmp) { > + printk(KERN_INFO "pick_eevdf curr: %p, se: %p\n", curr, se); > + mdelay(10); > + } > + return tmp; > + } > > if (curr && (!curr->on_rq || !entity_eligible(cfs_rq, curr))) > curr = NULL; > @@ -966,6 +976,11 @@ static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq) > if (!best || (curr && entity_before(curr, best))) > best = curr; > > + if (!best) { > + printk(KERN_INFO "best=%p, curr=%p, se=%p, node=%p ocrr=%p, ose=%p, onode=%p\n", best, curr, se, node, tmpcurr, tmpse, tmpnode); > + mdelay(10); > + } > + > return best; > } > >>>From the logs below: > [ 1355.763494] best=0000000000000000, curr=0000000000000000, se=00000000be02c573, node=0000000000000000 ocrr=0000000000000000, ose=00000000b1d4c4d5, onode=0000000023eb8c00 > > I have not been able to think of a quick reproducer to trigger a panic > https://lore.kernel.org/lkml/20240226082349.302363-1-yu.c.chen@intel.com/for this case. Hoping if someone can guide me on this. > > Note: The following dmesg log also contains a warning reported too. Panic > happens later. > > ------------[ cut here ]------------ > !se->on_rq > WARNING: CPU: 1 PID: 92333 at kernel/sched/fair.c:705 update_entity_lag+0xcc/0xf0 > Modules linked in: binfmt_misc bonding tls rfkill ibmveth pseries_rng vmx_crypto nd_pmem nd_btt dax_pmem loop nfnetlink xfs sd_mod papr_scm libnvdimm ibmvscsi scsi_transport_srp pseries_wdt dm_mirror dm_region_hash dm_log dm_mod fuse > CPU: 1 UID: 0 PID: 92333 Comm: genksyms Tainted: G W 6.11.0-master-with-print-10547-g684a64bf32b6-dirty #64 > Tainted: [W]=WARN > Hardware name: IBM,9080-HEX POWER10 (architected) hv:phyp pSeries > NIP: c0000000001cdfcc LR: c0000000001cdfc8 CTR: 0000000000000000 > REGS: c00000005c62ee50 TRAP: 0700 Tainted: G W (6.11.0-master-with-print-10547-g684a64bf32b6-dirty) > MSR: 8000000000029033 CR: 24002222 XER: 00000005 > CFAR: c000000000156a10 IRQMASK: 1 > GPR00: c0000000001cdfc8 c00000005c62f0f0 c000000001b57400 000000000000000a > GPR04: 00000000ffff7fff c00000005c62eee0 c00000005c62eed8 00000007fb050000 > GPR08: 0000000000000027 0000000000000000 0000000000000000 c000000002758de0 > GPR12: c000000002a18d88 c0000007fffef480 0000000000000000 0000000000000000 > GPR16: c000000002c56d40 0000000000000000 c00000005c62f5b4 0000000000000000 > GPR20: fffffffffffffdef 0000000000000000 0000000000000002 c000000003cd7300 > GPR24: 0000000000000000 0000000000000008 c0000007fd1d3f80 0000000000000000 > GPR28: 0000000000000001 0000000000000009 c0000007fd1d4080 c0000000656a0000 > NIP [c0000000001cdfcc] update_entity_lag+0xcc/0xf0 > LR [c0000000001cdfc8] update_entity_lag+0xc8/0xf0 > Call Trace: > [c00000005c62f0f0] [c0000000001cdfc8] update_entity_lag+0xc8/0xf0 (unreliable) > [c00000005c62f160] [c0000000001cea80] dequeue_entity+0xb0/0x6d0 > [c00000005c62f1f0] [c0000000001cf8b0] dequeue_entities+0x150/0x600 > [c00000005c62f2c0] [c0000000001d02a8] dequeue_task_fair+0x158/0x2e0 > [c00000005c62f300] [c0000000001b5ea4] dequeue_task+0x64/0x200 > [c00000005c62f380] [c0000000001cc950] detach_tasks+0x140/0x420 > [c00000005c62f3f0] [c0000000001d6044] sched_balance_rq+0x214/0x7c0 > [c00000005c62f550] [c0000000001d6830] sched_balance_newidle+0x240/0x630 > [c00000005c62f640] [c0000000001d6d0c] pick_next_task_fair+0x7c/0x4a0 > [c00000005c62f6d0] [c0000000001afc50] __pick_next_task+0x60/0x2d0 > [c00000005c62f730] [c0000000010e8ce8] __schedule+0x198/0x840 > [c00000005c62f810] [c0000000010e93d0] schedule+0x40/0x110 > [c00000005c62f880] [c00000000064c574] pipe_read+0x424/0x6a0 > [c00000005c62f960] [c00000000063a0fc] vfs_read+0x30c/0x3d0 > [c00000005c62fa10] [c00000000063adf4] ksys_read+0x104/0x160 > [c00000005c62fa60] [c000000000031678] system_call_exception+0x138/0x2d0 > [c00000005c62fe50] [c00000000000cedc] system_call_vectored_common+0x15c/0x2ec > --- interrupt: 3000 at 0x7fffb8f4a0c4 > NIP: 00007fffb8f4a0c4 LR: 00007fffb8f4a0c4 CTR: 0000000000000000 > REGS: c00000005c62fe80 TRAP: 3000 Tainted: G W (6.11.0-master-with-print-10547-g684a64bf32b6-dirty) > MSR: 800000000280f033 CR: 48004222 XER: 00000000 > IRQMASK: 0 > GPR00: 0000000000000003 00007fffe27ca2d0 00007fffb9067100 0000000000000000 > GPR04: 000000003076051b 0000000000002000 00007fffb9060b50 0000000000000000 > GPR08: 000000000000006f 0000000000000000 0000000000000000 0000000000000000 > GPR12: 0000000000000000 00007fffb917a560 000000000000000b 0000000000000000 > GPR16: 00007fffb9173570 0000000000002000 000000000000000c 000000000000000b > GPR20: 00000000307604c0 0000000030762509 00000000100484e8 0000000030762515 > GPR24: 0000000010022b80 0000000000000000 0000000000000005 0000000000002000 > GPR28: 000000003076051b 0000000000002000 00007fffb905e508 00007fffb9060b50 > NIP [00007fffb8f4a0c4] 0x7fffb8f4a0c4 > LR [00007fffb8f4a0c4] 0x7fffb8f4a0c4 > --- interrupt: 3000 > Code: 4e800020 3d220104 89297c19 2c090000 4082ff8c 3c62ff99 39200001 3d420104 38632d90 992a7c19 4bf88965 60000000 <0fe00000> 4bffff68 60000000 60000000 > ---[ end trace 0000000000000000 ]--- > best=0000000000000000, curr=0000000000000000, se=00000000be02c573, node=0000000000000000 ocrr=0000000000000000, ose=00000000b1d4c4d5, onode=0000000023eb8c00 > Kernel attempted to read user page (51) - exploit attempt? (uid: 0) > BUG: Kernel NULL pointer dereference on read at 0x00000051 > Faulting instruction address: 0xc0000000001cfebc > Oops: Kernel access of bad area, sig: 11 [#1] > LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries > Modules linked in: binfmt_misc bonding tls rfkill ibmveth pseries_rng vmx_crypto nd_pmem nd_btt dax_pmem loop nfnetlink xfs sd_mod papr_scm libnvdimm ibmvscsi scsi_transport_srp pseries_wdt dm_mirror dm_region_hash dm_log dm_mod fuse > CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G W 6.11.0-master-with-print-10547-g684a64bf32b6-dirty #64 > Tainted: [W]=WARN > Hardware name: IBM,9080-HEX POWER10 (architected) 0x800200 0xf000006 of:IBM,FW1060.00 (NH1060_012) hv:phyp pSeries > NIP: c0000000001cfebc LR: c0000000001cfebc CTR: 0000000000000000 > REGS: c000000002c13950 TRAP: 0300 Tainted: G W (6.11.0-master-with-print-10547-g684a64bf32b6-dirty) > MSR: 800000000280b033 CR: 44022282 XER: 0000000d > CFAR: c0000000001c4758 DAR: 0000000000000051 DSISR: 40000000 IRQMASK: 1 > GPR00: c0000000001cfebc c000000002c13bf0 c000000001b57400 0000000000000000 > GPR04: c0000007fd147108 c0000007fd1cd600 c000000002c13968 00000007fafb0000 > GPR08: 0000000000000027 00000000004e2002 0000896cdac1f9a0 0000000000002000 > GPR12: c000000002a18d88 c000000002f10000 0000000000000000 00000007fffe0000 > GPR16: 00000007fffd0000 0000000000000000 00000007fffe0114 0000000000000000 > GPR20: 0000000000000000 0000000000000000 c0000000010e95ec c000000002bd6380 > GPR24: c000000002bd6da8 c000000002c524e8 0000000000000000 c000000002bd6380 > GPR28: c000000002bd6380 c0000007fd1d3f80 c0000007fd1d4080 c0000007fd1d3f80 > NIP [c0000000001cfebc] pick_next_entity+0x3c/0x180 > LR [c0000000001cfebc] pick_next_entity+0x3c/0x180 > Call Trace: > [c000000002c13bf0] [c0000000001cfebc] pick_next_entity+0x3c/0x180 (unreliable) > [c000000002c13c70] [c0000000001d0064] pick_task_fair+0x64/0x130 > [c000000002c13cb0] [c0000000001d6cd8] pick_next_task_fair+0x48/0x4a0 > [c000000002c13d40] [c0000000001afc50] __pick_next_task+0x60/0x2d0 > [c000000002c13da0] [c0000000010e8ce8] __schedule+0x198/0x840 > [c000000002c13e80] [c0000000010e95ec] schedule_idle+0x3c/0x70 > [c000000002c13eb0] [c0000000001eb1d0] do_idle+0x160/0x1b0 > [c000000002c13f00] [c0000000001eb4d0] cpu_startup_entry+0x50/0x60 > [c000000002c13f30] [c0000000000110e8] rest_init+0xf0/0xf4 > [c000000002c13f60] [c0000000020053a4] do_initcalls+0x0/0x190 > [c000000002c13fe0] [c00000000000e788] start_here_common+0x1c/0x20 > Code: 60000000 7c0802a6 fba1ffe8 fbc1fff0 fbe1fff8 7c7d1b78 7c9e2378 f8010010 f821ff81 60000000 7fc3f378 4bff4601 <89230051> 7c7f1b78 2c090000 40820098 > ---[ end trace 0000000000000000 ]--- > pstore: backend (nvram) writing error (-1) > > Kernel panic - not syncing: Fatal exception > Rebooting in 10 seconds.. > > I have a feeling this might be what is described in this thread: https://lore.kernel.org/lkml/20240226082349.302363-1-yu.c.chen@intel.com/ Likely a result of an overflow for vruntime. And we come out of pick_eevdf without a valid entity.