From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id 779996B0033 for ; Wed, 18 Oct 2017 03:27:55 -0400 (EDT) Received: by mail-pg0-f69.google.com with SMTP id y184so2160514pgd.15 for ; Wed, 18 Oct 2017 00:27:55 -0700 (PDT) Received: from lgeamrelo11.lge.com (LGEAMRELO11.lge.com. [156.147.23.51]) by mx.google.com with ESMTP id r10si6467016pgp.392.2017.10.18.00.27.53 for ; Wed, 18 Oct 2017 00:27:54 -0700 (PDT) Date: Wed, 18 Oct 2017 16:31:29 +0900 From: Joonsoo Kim Subject: Re: [lkp-robot] [x86/kconfig] 81d3871900: BUG:unable_to_handle_kernel Message-ID: <20171018073128.GA27595@js1304-P5Q-DELUXE> References: <20171010121513.GC5445@yexl-desktop> <20171011023106.izaulhwjcoam55jt@treble> <20171011170120.7flnk6r77dords7a@treble> <20171017073326.GA23865@js1304-P5Q-DELUXE> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner Cc: Josh Poimboeuf , kernel test robot , Ingo Molnar , Andy Lutomirski , Borislav Petkov , Brian Gerst , Denys Vlasenko , "H. Peter Anvin" , Jiri Slaby , Linus Torvalds , Mike Galbraith , Peter Zijlstra , LKML , lkp@01.org, linux-mm@kvack.org, Pekka Enberg , David Rientjes , Andrew Morton , Christoph Lameter On Tue, Oct 17, 2017 at 09:50:04AM +0200, Thomas Gleixner wrote: > On Tue, 17 Oct 2017, Joonsoo Kim wrote: > > On Wed, Oct 11, 2017 at 12:01:20PM -0500, Josh Poimboeuf wrote: > > > > Looking at the panic, the code in slob_free() was: > > > > > > > > 0: e8 8d f7 ff ff callq 0xfffffffffffff792 > > > > 5: 48 ff 05 c9 8c 91 02 incq 0x2918cc9(%rip) # 0x2918cd5 > > > > c: 85 c0 test %eax,%eax > > > > e: 75 51 jne 0x61 > > > > 10: 49 0f bf c5 movswq %r13w,%rax > > > > 14: 48 ff 05 c2 8c 91 02 incq 0x2918cc2(%rip) # 0x2918cdd > > > > 1b: 48 8d 3c 43 lea (%rbx,%rax,2),%rdi > > > > 1f: 48 39 ef cmp %rbp,%rdi > > > > 22: 75 3d jne 0x61 > > > > 24: 48 ff 05 ba 8c 91 02 incq 0x2918cba(%rip) # 0x2918ce5 > > > > 2b:* 8b 6d 00 mov 0x0(%rbp),%ebp <-- trapping instruction > > > > 2e: 66 85 ed test %bp,%bp > > > > 31: 7e 09 jle 0x3c > > > > 33: 48 ff 05 b3 8c 91 02 incq 0x2918cb3(%rip) # 0x2918ced > > > > 3a: eb 05 jmp 0x41 > > > > 3c: bd .byte 0xbd > > > > 3d: 01 00 add %eax,(%rax) > > > > > > > > The slob_free() code tried to read four bytes at ffff88001c4afffe, and > > > > ended up reading past the page into a bad area. I think the bad address > > > > (ffff88001c4afffe) was returned from slob_next() and it panicked trying > > > > to read s->units in slob_units(). > > > > Hello, > > > > It looks like a compiler bug. The code of slob_units() try to read two > > bytes at ffff88001c4afffe. It's valid. But the compiler generates > > wrong code that try to read four bytes. > > > > static slobidx_t slob_units(slob_t *s) > > { > > if (s->units > 0) > > return s->units; > > return 1; > > } > > > > s->units is defined as two bytes in this setup. > > > > Wrongly generated code for this part. > > > > 'mov 0x0(%rbp), %ebp' > > > > %ebp is four bytes. > > > > I guess that this wrong four bytes read cross over the valid memory > > boundary and this issue happend. > > > > Proper code (two bytes read) is generated if different version of gcc > > is used. > > Which version fails to generate proper code and which versions work? > gcc 4.8 and 4.9 fails to generate proper code. gcc 5.1 and the latest version works fine. I guess that this problem is related to the corner case of some optimization feature since minor code change makes the result different. And, with -O2, proper code is generated even if gcc 4.8 is used. Thanks. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org