mm: BUG in expand_downwards

[Dmitry Vyukov]

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).