Hello, Recently I saw the following report : http://www.securityfocus.com/archive/1/539661 I've been testing that image and even on latest 4.9-rc4 I'm able to reproduce a crash. This seems rather indetermenistic in that it causes double/triple faults which causes my qemu guest to completely hang or reboot. However, on 4.9-rc4 with errors=panic mount options the crash looks like : [ 47.172026] BUG: unable to handle kernel NULL pointer dereference at 000000000000090f [ 47.172215] IP: [<ffffffff81090e3f>] update_curr+0x2f/0x210 [ 47.172342] PGD 0 [ 47.172389] [ 47.172438] Oops: 0000 [#1] SMP [ 47.172521] Modules linked in: [ 47.172627] CPU: 0 PID: 1108 Comm: mount Tainted: G W 4.9.0-rc4-clouder1 #30 [ 47.172777] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.8.1-0-g4adadbd-20150316_085822-nilsson.home.kraxel.org 04/01/2014 [ 47.173008] task: ffff8800068ec100 task.stack: ffff880006648000 [ 47.173008] RIP: 0010:[<ffffffff81090e3f>] [<ffffffff81090e3f>] update_curr+0x2f/0x210 [ 47.173008] RSP: 0018:ffff880007c03d68 EFLAGS: 00010082 [ 47.173008] RAX: ffffffffffffffff RBX: ffff880006630000 RCX: 0000000afbabb8be [ 47.173008] RDX: 0000000000000000 RSI: ffff8800068ec100 RDI: ffff880006630000 [ 47.173008] RBP: ffff880007c03da8 R08: 0000000000000022 R09: 0000000000000026 [ 47.173008] R10: 00000000005acec3 R11: 0000000000000000 R12: 0000000000016300 [ 47.173008] R13: ffffffffffffffff R14: ffff880006630000 R15: 0000000000000000 [ 47.173008] FS: 00007f08d69e97e0(0000) GS:ffff880007c00000(0000) knlGS:0000000000000000 [ 47.173008] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 47.173008] CR2: 000000000000090f CR3: 000000000665e000 CR4: 00000000000006f0 [ 47.173008] Stack: [ 47.173008] fffffffffffffed4 ffffffff820368e0 fffffffffffffed4 ffff8800068ec180 [ 47.173008] 0000000000016300 0000000000000000 ffff880006630000 0000000000000000 [ 47.173008] ffff880007c03e18 ffffffff81097c84 ffff880007c03df8 ffff880007c16dc0 [ 47.173008] Call Trace: [ 47.173008] <IRQ> [ 47.173008] [<ffffffff81097c84>] task_tick_fair+0x2a4/0x3f0 [ 47.173008] [<ffffffff81084fa8>] scheduler_tick+0x68/0xe0 [ 47.173008] [<ffffffff810c1c81>] update_process_times+0x51/0x70 [ 47.173008] [<ffffffff810d2bf8>] tick_sched_timer+0x58/0x180 [ 47.173008] [<ffffffff810c3678>] ? __remove_hrtimer+0x58/0x90 [ 47.173008] [<ffffffff810c3f07>] __hrtimer_run_queues+0xd7/0x290 [ 47.173008] [<ffffffff810d2ba0>] ? tick_setup_sched_timer+0x100/0x100 [ 47.173008] [<ffffffff8103b14d>] ? lapic_next_event+0x1d/0x30 [ 47.173008] [<ffffffff810ca54b>] ? ktime_get_update_offsets_now+0x5b/0x120 [ 47.173008] [<ffffffff8106100f>] ? __local_bh_enable+0x3f/0x70 [ 47.173008] [<ffffffff810c4252>] hrtimer_interrupt+0xa2/0x1e0 [ 47.173008] [<ffffffff8103b8d9>] local_apic_timer_interrupt+0x39/0x60 [ 47.173008] [<ffffffff816ac3a1>] smp_apic_timer_interrupt+0x41/0x55 [ 47.173008] [<ffffffff816ab699>] apic_timer_interrupt+0x89/0x90 [ 47.173008] <EOI> [ 47.173008] [<ffffffff8127d834>] ? ext4_calculate_overhead+0x264/0x470 [ 47.173008] [<ffffffff8127d81e>] ? ext4_calculate_overhead+0x24e/0x470 [ 47.173008] [<ffffffff8128b979>] ext4_fill_super+0x2019/0x3270 [ 47.173008] [<ffffffff81344483>] ? pointer+0x2a3/0x400 [ 47.173008] [<ffffffff811d0477>] mount_bdev+0x187/0x1d0 [ 47.173008] [<ffffffff81170a65>] ? __alloc_percpu+0x15/0x20 [ 47.173008] [<ffffffff81289960>] ? ext4_alloc_flex_bg_array+0x110/0x110 [ 47.173008] [<ffffffff8127aec5>] ext4_mount+0x15/0x20 [ 47.173008] [<ffffffff811cf3d3>] mount_fs+0x43/0x170 [ 47.173008] [<ffffffff811ef6d6>] vfs_kern_mount+0x76/0x130 [ 47.173008] [<ffffffff811f05f6>] do_mount+0x226/0xcb0 [ 47.173008] [<ffffffff8116a707>] ? memdup_user+0x57/0x90 [ 47.173008] [<ffffffff811f10fa>] SyS_mount+0x7a/0xc0 [ 47.173008] [<ffffffff816a9dea>] entry_SYSCALL_64_fastpath+0x18/0xa8 Without it I usually get a DF in the PF handler (ouch). However, Sebastian reported that on his 4.9-rc4 it doesn't crash: http://paste.debian.net/hidden/6fae7231/ PeterZ, ffffffff81090e3f is kernel/sched/fair.c:2727 - val >>= local_n / LOAD_AVG_PERIOD; in decay_load kernel/sched/fair.c:2850 kernel/sched/fair.c:3053 the 2727 line code seems very suspicious in that it doesn't work with any global memory hmmm... On older 4.4.x based kernel the symptoms range from DF/TF to memory corruption in the scheduler, to a crash on the last return statement in count_overhead. It's still puzzling how come ext4 can cause such a far reaching memory corruption that scheduler data structures are affected. Nikolay -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
