On Fri, 14 Mar 2014 11:05:51 +0800 Li Zefan <lizefan@xxxxxxxxxx> wrote: > Hi Davidlohr, > > On 2014/3/4 11:26, Linus Torvalds wrote: > > On Mon, Mar 3, 2014 at 7:13 PM, Davidlohr Bueso <davidlohr@xxxxxx> 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. > > ... > > [ 6072.027007] [<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 Yep. Please grab whichever of mm-per-thread-vma-caching-fix-3.patch mm-per-thread-vma-caching-fix-4.patch mm-per-thread-vma-caching-fix-5.patch mm-per-thread-vma-caching-fix-6-checkpatch-fixes.patch mm-per-thread-vma-caching-fix-6-fix.patch which you don't have from http://ozlabs.org/~akpm/mmots/broken-out/ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>