On Fri, 9 Nov 2012, Sasha Levin wrote: > On 11/05/2012 05:47 PM, Michel Lespinasse wrote: > > When CONFIG_DEBUG_VM_RB is enabled, check that rb_subtree_gap is > > correctly set for every vma and that mm->highest_vm_end is also correct. > > > > Also add an explicit 'bug' variable to track if browse_rb() detected any > > invalid condition. > > > > Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx> > > Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> > > > > --- > > Hi all, > > While fuzzing with trinity inside a KVM tools (lkvm) guest, using today's -next > kernel, I'm getting these: > > > [ 117.007714] free gap 7fba0dd1c000, correct 7fba0dcfb000 > [ 117.019773] map_count 750 rb -1 > [ 117.028362] ------------[ cut here ]------------ > [ 117.029813] kernel BUG at mm/mmap.c:439! > [ 117.031024] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC > [ 117.032933] Dumping ftrace buffer: > [ 117.033972] (ftrace buffer empty) > [ 117.035085] CPU 4 > [ 117.035676] Pid: 6859, comm: trinity-child46 Tainted: G W 3.7.0-rc4-next-20121109-sasha-00013-g9407f3c #124 > [ 117.038217] RIP: 0010:[<ffffffff81236687>] [<ffffffff81236687>] validate_mm+0x297/0x2c0 > [ 117.041056] RSP: 0018:ffff880016a4fdf8 EFLAGS: 00010296 > [ 117.041056] RAX: 0000000000000013 RBX: 00000000ffffffff RCX: 0000000000000006 > [ 117.041056] RDX: 0000000000005270 RSI: ffff880024120910 RDI: 0000000000000286 > [ 117.052131] RBP: ffff880016a4fe48 R08: 0000000000000000 R09: 0000000000000000 > [ 117.052131] R10: 0000000000000001 R11: 0000000000000000 R12: 00000000000002ee > [ 117.052131] R13: 00007fffea1fc000 R14: ffff88002412c000 R15: 0000000000000000 > [ 117.052131] FS: 00007fba129db700(0000) GS:ffff880063600000(0000) knlGS:0000000000000000 > [ 117.052131] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 117.052131] CR2: 0000000003323288 CR3: 00000000169b2000 CR4: 00000000000406e0 > [ 117.052131] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 117.052131] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > [ 117.052131] Process trinity-child46 (pid: 6859, threadinfo ffff880016a4e000, task ffff880024120000) > [ 117.052131] Stack: > [ 117.052131] ffffffff8489e201 ffffffff81235aa0 ffff88000885cac8 0000000100000000 > [ 117.052131] ffffffff812361b9 ffff88002412c000 ffff88000885cac8 ffff88000885cdc8 > [ 117.052131] ffff88000885cdd0 ffff88002412c000 ffff880016a4fe98 ffffffff812367b4 > [ 117.052131] Call Trace: > [ 117.052131] [<ffffffff81235aa0>] ? vma_compute_subtree_gap+0x40/0x40 > [ 117.052131] [<ffffffff812361b9>] ? vma_gap_update+0x19/0x30 > [ 117.052131] [<ffffffff812367b4>] vma_link+0x94/0xe0 > [ 117.052131] [<ffffffff812386c4>] do_brk+0x2c4/0x380 > [ 117.052131] [<ffffffff812387bf>] ? sys_brk+0x3f/0x190 > [ 117.052131] [<ffffffff812388ce>] sys_brk+0x14e/0x190 > [ 117.052131] [<ffffffff83be2618>] tracesys+0xe1/0xe6 > [ 117.052131] Code: d8 41 8b 76 60 39 de 74 1b 89 da 48 c7 c7 c6 d9 89 84 31 c0 e8 01 76 94 02 eb 10 66 0f 1f 84 00 00 00 00 00 > 8b 45 c8 85 c0 74 18 <0f> 0b 4c 8d 48 e0 48 8b 70 e0 31 db c7 45 cc 00 00 00 00 e9 f4 > [ 117.052131] RIP [<ffffffff81236687>] validate_mm+0x297/0x2c0 > [ 117.052131] RSP <ffff880016a4fdf8> > [ 117.136092] ---[ end trace 5ce250e0bf6d040c ]--- > > Note that they are very easy to reproduce. > > Also, I see that lots of the code there has a local variable named 'bug' thats tracking > whether we should BUG() later on. Why does it work that way and the BUG() isn't immediate? 3.7.0-rc4-mm1 BUGged on mm/mmap.c:439 as soon as I tried to rebuild that kernel with Alan's tty/vt/fb patch included, no fuzzing required. free_gap 55551d077000, correct 55551ccd2000 in my case. It should only be affecting the minority with CONFIG_DEBUG_VM_RB=y. I've put #if 0 around the rb_subtree_gap checking block in browse_rb(), and running okay so far with that - but not yet done much with it. Hugh
