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Date: Thu, 25 Sep 2008 17:20:49 +0200 From: "Vegard Nossum" <vegard.nossum@...il.com> To: "H. Peter Anvin" <hpa@...or.com> Cc: "Ingo Molnar" <mingo@...e.hu>, x86@...nel.org, linux-kernel@...r.kernel.org, "Thomas Gleixner" <tglx@...utronix.de> Subject: Re: v2.6.27-rc7: x86: #GP on panic? On Thu, Sep 25, 2008 at 4:07 PM, Vegard Nossum <vegard.nossum@...il.com> wrote: > On Thu, Sep 25, 2008 at 10:53 AM, H. Peter Anvin <hpa@...or.com> wrote: >> Ingo Molnar wrote: >>> >>> * Vegard Nossum <vegard.nossum@...il.com> wrote: >>> >>>> Hi, >>>> >>>> With 2.6.27-rc7 on qemu-x86_64, it seems that panic will trigger a >>>> General Protection Fault. I haven't seen it before. >>> >>>> [ 4.523641] Code: eb fd 55 48 89 e5 53 51 83 3d 25 e8 78 00 00 75 >>>> 1a 31 d2 31 f6 48 c7 c7 e1 9c 01 81 e8 f7 a4 03 00 9c 5b fa e8 94 09 >>>> 00 00 53 9d <5a> 5b c9 c3 55 31 c0 48 89 e5 89 04 25 b0 c0 5f ff 65 83 >>>> 04 25 >>> >>> hm, 0x5a is a simple pop %rdx. A #GP there means the stack segment is >>> bust? >>> >> >> No, that would be #SS (and segments don't really exist in 64-bit mode >> anyway.) In 32-bit mode it could mean a code segment overrun. >> >> *However*... >> >> [ 4.523477] general protection fault: fff2 [1] SMP >> >> There is an error code attached to the #GP, which is supposed to mean that >> somehow a segment selector was involved. This doesn't look like a very valid >> segment selector at all. >> >>> hm: >>> >>>> ffffffff8101a6b9 <disable_local_APIC> >>>> ffffffff81019d25: 53 push %rbx >>>> ffffffff81019d26: 9d popfq >>>> ffffffff81019d27: 5a pop %rdx >>> >>> so it's preceded by a popfq and on the next instruction we #GP. >>> >>> but the stack and flags state looks good: >>> >>> [ 4.523641] RSP: 0018:ffff880007867d70 EFLAGS: 00000286 >>> >> >> My guess is that the popfq enables interrupts, and we try to take an >> interrupt through an IDT entry which isn't set up correctly. > > I'm sorry for the false alarm. I discovered that it did not happen on > a clean kernel. My kernel was using this patch. No, I was wrong! It *does* happen for vanilla as well, but it doesn't happen reliably. [ 4.043370] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0) [ 4.048765] general protection fault: fff2 [1] SMP [ 4.048765] CPU 0 [ 4.048765] Modules linked in: [ 4.048765] Pid: 1, comm: swapper Tainted: G W 2.6.27-rc7 #8 [ 4.048765] RIP: 0010:[<ffffffff81019d27>] [<ffffffff81019d27>] native_smp_send_stop+0x29/0x2d [ 4.048765] RSP: 0018:ffff880007867d70 EFLAGS: 00000286 [ 4.048765] RAX: 00000000000000ff RBX: 0000000000000286 RCX: 0000000000000000 [ 4.048765] RDX: 0000000000000005 RSI: ffffffff81019ce1 RDI: 0000000000000000 [ 4.048765] RBP: ffff880007867d80 R08: 0000000000000000 R09: ffff880087867bff [ 4.048765] R10: ffff880087867bff R11: 000000000000000a R12: ffff88000707b018 [ 4.048765] R13: ffff88000707b000 R14: 0000000000008001 R15: ffffffff8159d550 [ 4.048765] FS: 0000000000000000(0000) GS:ffffffff816fae00(0000) knlGS:0000000000000000 [ 4.048765] CS: 0010 DS: 0018 ES: 0018 CR0: 000000008005003b [ 4.048765] CR2: 0000000000000000 CR3: 0000000000201000 CR4: 00000000000006a0 [ 4.048765] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 4.048765] DR3: 0000000000000000 DR6: 0000000000000000 DR7: 0000000000000000 [ 4.048765] Process swapper (pid: 1, threadinfo ffff880007866000, task ffff880007868000) [ 4.048765] Stack: 000000000000506f ffffffff8159d52d ffff880007867e70 ffffffff81034454 [ 4.048765] 0000003000000010 ffff880007867e80 ffff880007867db0 ffff880007867e80 [ 4.048765] ffff880007867dd0 ffff880007867e80 ffff880007899360 000000000000500e [ 4.048765] Call Trace: [ 4.048765] [<ffffffff81034454>] panic+0xe8/0x193 [ 4.048765] [<ffffffff8118ef5f>] ? kobject_put+0x44/0x49 [ 4.048765] [<ffffffff8121778e>] ? put_device+0x15/0x17 [ 4.048765] [<ffffffff8121ad49>] ? class_for_each_device+0xfe/0x10e [ 4.048765] [<ffffffff81715059>] mount_block_root+0x1ee/0x205 [ 4.048765] [<ffffffff81009417>] ? name_to_dev_t+0x1bb/0xda4 [ 4.048765] [<ffffffff817152cd>] mount_root+0xe5/0xea [ 4.048765] [<ffffffff81715449>] prepare_namespace+0x177/0x1a4 [ 4.048765] [<ffffffff810aaede>] ? putname+0x37/0x39 [ 4.048765] [<ffffffff81714d0f>] kernel_init+0x16a/0x178 [ 4.048765] [<ffffffff8102bde3>] ? schedule_tail+0x24/0x5d [ 4.048765] [<ffffffff8100cf79>] child_rip+0xa/0x11 [ 4.048765] [<ffffffff811b92a4>] ? acpi_ds_init_one_object+0x0/0x88 [ 4.048765] [<ffffffff81714ba5>] ? kernel_init+0x0/0x178 [ 4.048765] [<ffffffff8100cf6f>] ? child_rip+0x0/0x11 [ 4.048765] [ 4.048765] [ 4.048765] Code: eb fd 55 48 89 e5 53 51 83 3d 25 e8 78 00 00 75 1a 31 d2 31 f6 48 c7 c7 e1 9c 01 81 e8 a7 a4 03 00 9c 5b fa e8 94 09 00 00 53 9d <5a> 5b c9 c3 55 31 c0 48 89 e5 89 04 25 b0 c0 5f ff 65 83 04 25 [ 4.048765] RIP [<ffffffff81019d27>] native_smp_send_stop+0x29/0x2d [ 4.048765] RSP <ffff880007867d70> [ 4.048765] ---[ end trace 4eaa2a86a8e2da22 ]--- This was after 49 successful boots (qemu running the same clean kernel in a loop over and over). Could be a qemu thing, though. Vegard -- "The animistic metaphor of the bug that maliciously sneaked in while the programmer was not looking is intellectually dishonest as it disguises that the error is the programmer's own creation." -- E. W. Dijkstra, EWD1036 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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