Re: mm: BUG in expand_downwards

[Dmitry Vyukov]

On Wed, Jan 27, 2016 at 12:49 PM, Konstantin Khlebnikov
<koct9i@xxxxxxxxx> wrote:
> It seems anon_vma appeared between lock and unlock.
>
> This should fix the bug and make code faster (write lock isn't required here)
>
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -453,12 +453,16 @@ static void validate_mm(struct mm_struct *mm)
>         struct vm_area_struct *vma = mm->mmap;
>
>         while (vma) {
> +               struct anon_vma *anon_vma = vma->anon_vma;
>                 struct anon_vma_chain *avc;
>
> -               vma_lock_anon_vma(vma);
> -               list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
> -                       anon_vma_interval_tree_verify(avc);
> -               vma_unlock_anon_vma(vma);
> +               if (anon_vma) {
> +                       anon_vma_lock_read(anon_vma);
> +                       list_for_each_entry(avc, &vma->anon_vma_chain, same_vma)
> +                               anon_vma_interval_tree_verify(avc);
> +                       anon_vma_unlock_read(anon_vma);
> +               }
> +
>                 highest_address = vma->vm_end;
>                 vma = vma->vm_next;
>                 i++;


Now testing with this patch. Thanks for quick fix!

> On Wed, Jan 27, 2016 at 1:51 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> Hello,
>>
>> The following program trigger BUG in expand_downwards (run it in tight
>> parallel loop for a while):
>>
>> // autogenerated by syzkaller (http://github.com/google/syzkaller)
>> #include <pthread.h>
>> #include <stdint.h>
>> #include <string.h>
>> #include <sys/syscall.h>
>> #include <unistd.h>
>>
>> long r[10];
>>
>> void* thr(void* arg)
>> {
>>   switch ((long)arg) {
>>   case 0:
>>     r[0] = syscall(SYS_mmap, 0x20731000ul, 0x2000ul, 0x2ul, 0x22132ul,
>>                    0xfffffffffffffffful, 0x0ul);
>>     break;
>>   case 1:
>>     r[1] = syscall(SYS_mremap, 0x20732000ul, 0x1000ul, 0x3000ul, 0x3ul,
>>                    0x2015b000ul, 0);
>>     break;
>>   case 2:
>>     r[2] = syscall(SYS_fanotify_init, 0x20ul, 0x40002ul, 0, 0, 0, 0);
>>     break;
>>   case 3:
>>     r[3] = syscall(SYS_mremap, 0x2015c000ul, 0x1000ul, 0x4000ul, 0x3ul,
>>                    0x204eb000ul, 0);
>>     break;
>>   case 4:
>>     r[4] = syscall(SYS_munlock, 0x204eb000ul, 0x4000ul, 0, 0, 0, 0);
>>     break;
>>   case 5:
>>     r[5] = syscall(SYS_mremap, 0x204ec000ul, 0x1000ul, 0x1000ul, 0x3ul,
>>                    0x2015d000ul, 0);
>>     break;
>>   case 6:
>>     r[6] = syscall(SYS_mmap, 0x20000000ul, 0x1000ul, 0x3ul, 0x32ul,
>>                    0xfffffffffffffffful, 0x0ul);
>>     break;
>>   case 7:
>>     r[7] = syscall(SYS_sigaltstack, 0x204ec000ul, 0x20000000ul, 0, 0, 0,
>>                    0);
>>     break;
>>   case 8:
>>     memcpy((void*)0x2015bffa, "\x2e\x2f\x62\x75\x73\x00", 6);
>>     r[9] = syscall(SYS_mkdir, 0x2015bffaul, 0x108ul, 0, 0, 0, 0);
>>     break;
>>   }
>>   return 0;
>> }
>>
>> int main()
>> {
>>   long i;
>>   pthread_t th[9];
>>
>>   srand(getpid());
>>   memset(r, -1, sizeof(r));
>>   for (i = 0; i < 9; i++) {
>>     pthread_create(&th[i], 0, thr, (void*)i);
>>     usleep(1000);
>>   }
>>   for (i = 0; i < 9; i++) {
>>     pthread_create(&th[i], 0, thr, (void*)i);
>>     usleep(rand()%1000);
>>   }
>>   usleep(10000);
>>   return 0;
>> }
>>
>>
>>
>> =====================================
>> [ BUG: bad unlock balance detected! ]
>> 4.5.0-rc1+ #292 Not tainted
>> -------------------------------------
>> a.out/7506 is trying to release lock (&anon_vma->rwsem) at:
>> [<     inline     >] vma_unlock_anon_vma include/linux/rmap.h:123
>> [<ffffffff816f8e5d>] validate_mm+0x12d/0x850 mm/mmap.c:461
>> but there are no more locks to release!
>>
>> other info that might help us debug this:
>> 1 lock held by a.out/7506:
>>  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff8127dfd7>]
>> __do_page_fault+0x737/0x960 arch/x86/mm/fault.c:1184
>>
>> stack backtrace:
>> CPU: 1 PID: 7506 Comm: a.out Not tainted 4.5.0-rc1+ #292
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>>  00000000ffffffff ffff88005d107b50 ffffffff829e79ad ffff8800603b4ce8
>>  ffff88005f15df00 ffffffff816f8e5d ffff88005d107b80 ffffffff81450884
>>  ffff8800603b4ce8 ffff88005f15e720 ffff88005f15e720 00000000ffffffff
>> Call Trace:
>>  [<     inline     >] __dump_stack lib/dump_stack.c:15
>>  [<ffffffff829e79ad>] dump_stack+0x6f/0xa2 lib/dump_stack.c:50
>>  [<ffffffff81450884>] print_unlock_imbalance_bug+0x174/0x1a0
>> kernel/locking/lockdep.c:3261
>>  [<     inline     >] __lock_release kernel/locking/lockdep.c:3385
>>  [<ffffffff8145c687>] lock_release+0x937/0xce0 kernel/locking/lockdep.c:3606
>>  [<ffffffff814490ba>] up_write+0x1a/0x60 kernel/locking/rwsem.c:91
>>  [<     inline     >] vma_unlock_anon_vma include/linux/rmap.h:123
>>  [<ffffffff816f8e5d>] validate_mm+0x12d/0x850 mm/mmap.c:461
>>  [<ffffffff817034be>] expand_downwards+0x19e/0xb30 mm/mmap.c:2283
>>  [<ffffffff81703ecb>] expand_stack+0x7b/0xe0 mm/mmap.c:2338
>>  [<ffffffff8127df88>] __do_page_fault+0x6e8/0x960 arch/x86/mm/fault.c:1217
>>  [<ffffffff8127e358>] trace_do_page_fault+0xe8/0x420 arch/x86/mm/fault.c:1331
>>  [<ffffffff8126f514>] do_async_page_fault+0x14/0xd0 arch/x86/kernel/kvm.c:264
>>  [<ffffffff8645bdf8>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:986
>>  [<     inline     >] SYSC_sigaltstack kernel/signal.c:3157
>>  [<ffffffff8138600c>] SyS_sigaltstack+0x6c/0x90 kernel/signal.c:3155
>>  [<ffffffff86459ab6>] entry_SYSCALL_64_fastpath+0x16/0x7a
>> arch/x86/entry/entry_64.S:185
>> mmap: free gap 1000, correct 0
>> mm ffff8800603a4e00 mmap ffff88005fc794c0 seqnum 12 task_size 140737488351232
>> get_unmapped_area ffffffff811af470
>> mmap_base 140584500215808 mmap_legacy_base 47048170172416
>> highest_vm_end 140737437655040
>> pgd ffff88005fc20000 mm_users 2 mm_count 1 nr_ptes 25 nr_pmds 3 map_count 49
>> hiwater_rss 7 hiwater_vm 813a total_vm 913e locked_vm 2
>> pinned_vm 0 data_vm 902e exec_vm d1 stack_vm 2a
>> start_code 400000 end_code 4ce986 start_data 6cee90 end_data 6d0d88
>> start_brk 934000 brk 957000 start_stack 7ffffcf5e660
>> arg_start 7ffffcf5feae arg_end 7ffffcf5feb6 env_start 7ffffcf5feb6
>> env_end 7ffffcf5fff0
>> binfmt ffffffff8797c260 flags cd core_state           (null)
>> ioctx_table           (null)
>> owner ffff88005d99df00 exe_file ffff880033321680
>> mmu_notifier_mm           (null)
>> flags: 0x0()
>> ------------[ cut here ]------------
>> kernel BUG at mm/mmap.c:481!
>> invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN
>> Modules linked in:
>> CPU: 1 PID: 9534 Comm: a.out Not tainted 4.5.0-rc1+ #292
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>> task: ffff880031522f80 ti: ffff8800314f8000 task.ti: ffff8800314f8000
>> RIP: 0010:[<ffffffff816f922c>]  [<ffffffff816f922c>] validate_mm+0x4fc/0x850
>> RSP: 0018:ffff8800314ffc60  EFLAGS: 00010286
>> RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000000
>> RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffffed000629ff22
>> RBP: ffff8800314ffcc8 R08: 0000000000000001 R09: 0000000000000000
>> R10: 0000000000000003 R11: 1ffffffff12e43c4 R12: 0000000000000031
>> R13: 0000000000000000 R14: 00007ffffcfa4000 R15: dffffc0000000000
>> FS:  00007fdc59313700(0000) GS:ffff88003ed00000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> CR2: 00000000204ec000 CR3: 000000005fc20000 CR4: 00000000000006e0
>> Stack:
>>  0000000000486f70 ffff8800603a4e60 ffff8800603a4e00 0000003100000001
>>  0000000000000000 0000000000041000 ffff88005fc78538 ffff88005fc78530
>>  ffff880032870a60 0000000000000000 ffff880031e61e00 000000001f6a9000
>> Call Trace:
>>  [<ffffffff817034be>] expand_downwards+0x19e/0xb30 mm/mmap.c:2283
>>  [<ffffffff81703ecb>] expand_stack+0x7b/0xe0 mm/mmap.c:2338
>>  [<ffffffff8127df88>] __do_page_fault+0x6e8/0x960 arch/x86/mm/fault.c:1217
>>  [<ffffffff8127e358>] trace_do_page_fault+0xe8/0x420 arch/x86/mm/fault.c:1331
>>  [<ffffffff8126f514>] do_async_page_fault+0x14/0xd0 arch/x86/kernel/kvm.c:264
>>  [<ffffffff8645bdf8>] async_page_fault+0x28/0x30 arch/x86/entry/entry_64.S:986
>>  [<     inline     >] SYSC_sigaltstack kernel/signal.c:3157
>>  [<ffffffff8138600c>] SyS_sigaltstack+0x6c/0x90 kernel/signal.c:3155
>>  [<ffffffff86459ab6>] entry_SYSCALL_64_fastpath+0x16/0x7a
>> arch/x86/entry/entry_64.S:185
>> Code: 58 60 44 39 e3 74 73 e8 03 0f e7 ff 44 89 e2 89 de 48 c7 c7 a0
>> dc 5a 86 e8 e7 c3 f4 ff e8 ed 0e e7 ff 48 8b 7d a8 e8 24 00 fe ff <0f>
>> 0b e8 dd 0e e7 ff 8b 55 b4 44 89 e6 48 c7 c7 40 dc 5a 86 e8
>> RIP  [<ffffffff816f922c>] validate_mm+0x4fc/0x850 mm/mmap.c:481
>>  RSP <ffff8800314ffc60>
>> ---[ end trace 5282aed32b3391b4 ]---
>>
>>
>> And there seems to be some locking issue in validate_mm.
>>
>> On commit 92e963f50fc74041b5e9e744c330dca48e04f08d (Jan 24).