mm: uninterruptable tasks hanged on mmap_sem

[Dmitry Vyukov]

Hello,

If the following program run in a parallel loop, eventually it leaves
hanged uninterruptable tasks on mmap_sem.

[ 4074.740298] sysrq: SysRq : Show Locks Held
[ 4074.740780] Showing all locks held in the system:
...
[ 4074.762133] 1 lock held by a.out/1276:
[ 4074.762427]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff816df89c>]
__mm_populate+0x25c/0x350
[ 4074.763149] 1 lock held by a.out/1147:
[ 4074.763438]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff816b3bbc>]
vm_mmap_pgoff+0x12c/0x1b0
[ 4074.764164] 1 lock held by a.out/1284:
[ 4074.764447]  #0:  (&mm->mmap_sem){++++++}, at: [<ffffffff816df89c>]
__mm_populate+0x25c/0x350
[ 4074.765287]

They all look as follows:

# cat /proc/1284/task/**/stack
[<ffffffff82c14d13>] call_rwsem_down_write_failed+0x13/0x20
[<ffffffff816b3bbc>] vm_mmap_pgoff+0x12c/0x1b0
[<ffffffff81700c58>] SyS_mmap_pgoff+0x208/0x580
[<ffffffff811aeeb6>] SyS_mmap+0x16/0x20
[<ffffffff86660276>] entry_SYSCALL_64_fastpath+0x16/0x7a
[<ffffffffffffffff>] 0xffffffffffffffff
[<ffffffff8164893e>] wait_on_page_bit+0x1de/0x210
[<ffffffff8165572b>] filemap_fault+0xfeb/0x14d0
[<ffffffff816e1972>] __do_fault+0x1b2/0x3e0
[<ffffffff816f080e>] handle_mm_fault+0x1b4e/0x49a0
[<ffffffff816ddae0>] __get_user_pages+0x2c0/0x11a0
[<ffffffff816df5a8>] populate_vma_page_range+0x198/0x230
[<ffffffff816df83b>] __mm_populate+0x1fb/0x350
[<ffffffff816f90c1>] do_mlock+0x291/0x360
[<ffffffff816f962b>] SyS_mlock2+0x4b/0x70
[<ffffffff86660276>] entry_SYSCALL_64_fastpath+0x16/0x7a
[<ffffffffffffffff>] 0xffffffffffffffff

# cat /proc/1284/status
Name: a.out
State: D (disk sleep)
Tgid: 1147
Ngid: 0
Pid: 1284
PPid: 28436
TracerPid: 0
Uid: 0 0 0 0
Gid: 0 0 0 0
FDSize: 64
Groups: 0
NStgid: 1147
NSpid: 1284
NSpgid: 28436
NSsid: 6529
VmPeak:   50356 kB
VmSize:   50356 kB
VmLck:      16 kB
VmPin:       0 kB
VmHWM:       8 kB
VmRSS:       8 kB
RssAnon:       8 kB
RssFile:       0 kB
RssShmem:       0 kB
VmData:   49348 kB
VmStk:     136 kB
VmExe:     828 kB
VmLib:       8 kB
VmPTE:      44 kB
VmPMD:      12 kB
VmSwap:       0 kB
HugetlbPages:       0 kB
Threads: 2
SigQ: 1/3189
SigPnd: 0000000000000100
ShdPnd: 0000000000000100
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000180000000
CapInh: 0000000000000000
CapPrm: 0000003fffffffff
CapEff: 0000003fffffffff
CapBnd: 0000003fffffffff
CapAmb: 0000000000000000
Seccomp: 0
Cpus_allowed: f
Cpus_allowed_list: 0-3
Mems_allowed: 00000000,00000003
Mems_allowed_list: 0-1
voluntary_ctxt_switches: 3
nonvoluntary_ctxt_switches: 1


There are no BUGs, WARNINGs, stalls on console.

Not sure if its mm or floppy fault.


// autogenerated by syzkaller (http://github.com/google/syzkaller)
#include <pthread.h>
#include <stdint.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>

#ifndef SYS_mlock2
#define SYS_mlock2 325
#endif

long r[7];

void* thr(void* arg)
{
  switch ((long)arg) {
  case 0:
    r[0] = syscall(SYS_mmap, 0x20000000ul, 0x1000ul, 0x3ul, 0x32ul,
                   0xfffffffffffffffful, 0x0ul);
    break;
  case 1:
    memcpy((void*)0x20000000, "\x2f\x64\x65\x76\x2f\x66\x64\x23", 8);
    r[2] = syscall(SYS_open, "/dev/fd0", 0x800ul, 0, 0, 0);
    break;
  case 2:
    r[3] = syscall(SYS_mmap, 0x20001000ul, 0x1000ul, 0x3ul, 0x32ul,
                   0xfffffffffffffffful, 0x0ul);
    break;
  case 3:
    r[4] = syscall(SYS_mmap, 0x20002000ul, 0x1000ul, 0x3ul, 0x812ul,
                   r[2], 0x0ul);
    break;
  case 4:
    r[5] = syscall(SYS_mmap, 0x20003000ul, 0x1000ul, 0x3ul, 0x32ul,
                   0xfffffffffffffffful, 0x0ul);
    break;
  case 5:
    r[6] = syscall(SYS_mlock2, 0x20000000ul, 0x4000ul, 0x0ul, 0, 0, 0);
    break;
  }
  return 0;
}

int main()
{
  long i;
  pthread_t th[6];

  srand(getpid());
  memset(r, -1, sizeof(r));
  for (i = 0; i < 6; i++) {
    pthread_create(&th[i], 0, thr, (void*)i);
    usleep(10000);
  }
  for (i = 0; i < 6; i++) {
    pthread_create(&th[i], 0, thr, (void*)i);
    if (rand() % 2)
      usleep(rand() % 10000);
  }
  usleep(100000);
  return 0;
}

On commit 36f90b0a2ddd60823fe193a85e60ff1906c2a9b3.