Hi Davidlohr, On 2014/3/4 11:26, Linus Torvalds wrote: > On Mon, Mar 3, 2014 at 7:13 PM, Davidlohr Bueso <davidl...@hp.com> wrote: >> >> Yes, I shortly realized that was silly... but I can say for sure it can >> happen and a quick qemu run confirms it. So I see your point as to >> asking why we need it, so now I'm looking for an explanation in the >> code. > > We definitely *do* have users. > > One example would be ptrace -> access_process_vm -> __access_remote_vm > -> get_user_pages() -> find_extend_vma() -> find_vma_prev -> find_vma. >
I raw this oops on 3.14.0-rc5-next-20140307, which is possible caused by your patch? Don't know how it was triggered. [ 6072.026715] BUG: unable to handle kernel NULL pointer dereference at 00000000000007f8 [ 6072.026729] IP: [<ffffffff811a0189>] follow_page_mask+0x69/0x620 [ 6072.026742] PGD c1975f067 PUD c19479067 PMD 0 [ 6072.026749] Oops: 0000 [#1] SMP [ 6072.026852] CPU: 2 PID: 13445 Comm: ps Not tainted 3.14.0-rc5-next-20140307-0.1-default+ #4 [ 6072.026863] Hardware name: Huawei Technologies Co., Ltd. Tecal RH2285 /BC11BTSA , BIO S CTSAV036 04/27/2011 [ 6072.026872] task: ffff88061d8848a0 ti: ffff880618854000 task.ti: ffff880618854000 [ 6072.026880] RIP: 0010:[<ffffffff811a0189>] [<ffffffff811a0189>] follow_page_mask+0x69/0x620 [ 6072.026889] RSP: 0018:ffff880618855c18 EFLAGS: 00010206 [ 6072.026895] RAX: 00000000000000ff RBX: ffffffffffffffea RCX: ffff880618855d0c [ 6072.026902] RDX: 0000000000000000 RSI: 00007fff0a474cc7 RDI: ffff88061aef8f00 [ 6072.026909] RBP: ffff880618855c88 R08: 0000000000000002 R09: 0000000000000000 [ 6072.026916] R10: 0000000000000000 R11: 0000000000003485 R12: 00007fff0a474cc7 [ 6072.026924] R13: 0000000000000016 R14: ffff88061aef8f00 R15: ffff880c1c842508 [ 6072.026932] FS: 00007f4687701700(0000) GS:ffff880c26a00000(0000) knlGS:0000000000000000 [ 6072.026940] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 6072.026947] CR2: 00000000000007f8 CR3: 0000000c184ee000 CR4: 00000000000007e0 [ 6072.026955] Stack: [ 6072.026959] ffff880618855c48 ffff880618855d0c 0000000018855c58 0000000000000246 [ 6072.026969] 0000000000000000 0000000000000752 ffffffff817c975c 0000000000000000 [ 6072.026980] ffff880618855c88 0000000000000016 ffff880c1c842508 ffff88061d8848a0 [ 6072.026989] Call Trace: [ 6072.026998] [<ffffffff811a4b14>] __get_user_pages+0x204/0x5a0 [ 6072.027007] [<ffffffff811a4f62>] get_user_pages+0x52/0x60 [ 6072.027015] [<ffffffff811a5088>] __access_remote_vm+0x118/0x1f0 [ 6072.027023] [<ffffffff811a51bb>] access_process_vm+0x5b/0x80 [ 6072.027033] [<ffffffff812675a7>] proc_pid_cmdline+0x77/0x120 [ 6072.027041] [<ffffffff81267da2>] proc_info_read+0xa2/0xe0 [ 6072.027050] [<ffffffff811f439d>] vfs_read+0xad/0x1a0 [ 6072.027057] [<ffffffff811f45b5>] SyS_read+0x65/0xb0 [ 6072.027066] [<ffffffff8159ba12>] system_call_fastpath+0x16/0x1b [ 6072.027072] Code: f4 4c 89 f7 89 45 a4 e8 36 0e eb ff 48 3d 00 f0 ff ff 48 89 c3 0f 86 d7 00 00 00 4c 89 e0 49 8b 56 40 48 c1 e8 27 25 ff 01 00 00 <48> 8b 0c c2 48 85 c9 75 3e 41 83 e5 08 74 1b 49 8b 87 90 00 00 [ 6072.027134] RIP [<ffffffff811a0189>] follow_page_mask+0x69/0x620 [ 6072.027142] RSP <ffff880618855c18> [ 6072.027146] CR2: 00000000000007f8 [ 6072.134516] ---[ end trace 8d006e01f05d1ba8 ]--- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
