Re: mm: BUG in expand_downwards

From: Konstantin Khlebnikov
Date: Wed Jan 27 2016 - 06:50:03 EST

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++;


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).