On Thu, Sep 10, 2015 at 03:27:59PM +0200, Andrey Konovalov wrote: > Can a vma be shared among a few mm's? Define "shared". vma can belong only to one process (mm_struct), but it can be accessed from other process like in rmap case below. rmap uses anon_vma_lock for anon vma and i_mmap_rwsem for file vma to make sure that the vma will not disappear under it. > If yes, then taking current->mm->mmap_sem to protect vma is not enough. Depends on what protection you are talking about. > In the first report below both T378 and T398 take > current->mm->mmap_sem at mm/mlock.c:650, but they turn out to be > different locks (the addresses are different). See i_mmap_lock_read() in T398. It will guarantee that vma is there. > In the second report T309 doesn't take any locks at all, since it > assumes that after checking atomic_dec_and_test(&mm->mm_users) the mm > has no other users, but then it does a write to vma. This one is tricky. I *assume* the mm cannot be generally accessible after mm_users drops to zero, but I'm not entirely sure about it. procfs? ptrace? The VMA is still accessible via rmap at this point. And I think it can be a problem: CPU0 CPU1 exit_mmap() // mmap_sem is *not* taken munlock_vma_pages_all() munlock_vma_pages_range() try_to_unmap_one() down_read_trylock(&vma->vm_mm->mmap_sem)) !!(vma->vm_flags & VM_LOCKED) == true vma->vm_flags &= ~VM_LOCKED; <munlock the page> mlock_vma_page(page); // mlocked pages is leaked. The obvious solution is to take mmap_sem in exit path, but it would cause performance regression. Any comments? > > ================================================================== > ThreadSanitizer: data-race in munlock_vma_pages_range > > Write of size 8 by thread T378 (K2633, CPU3): > [<ffffffff81212579>] munlock_vma_pages_range+0x59/0x3e0 mm/mlock.c:425 > [<ffffffff81212ac9>] mlock_fixup+0x1c9/0x280 mm/mlock.c:549 > [<ffffffff81212ccc>] do_mlock+0x14c/0x180 mm/mlock.c:589 > [< inlined >] SYSC_munlock mm/mlock.c:651 > [<ffffffff812130b4>] SyS_munlock+0x74/0xb0 mm/mlock.c:643 > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > Locks held by T378: > #0 Lock 25710428 taken here: > [< inlined >] SYSC_munlock mm/mlock.c:650 > [<ffffffff8121308c>] SyS_munlock+0x4c/0xb0 mm/mlock.c:643 > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > Previous read of size 8 by thread T398 (K2623, CPU2): > [<ffffffff8121d198>] try_to_unmap_one+0x78/0x4f0 mm/rmap.c:1208 > [< inlined >] rmap_walk_file mm/rmap.c:1540 > [<ffffffff8121e7b7>] rmap_walk+0x147/0x450 mm/rmap.c:1559 > [<ffffffff8121ef72>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > [<ffffffff81211bb0>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > [<ffffffff81212066>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > [<ffffffff812128a0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > [<ffffffff81212ac9>] mlock_fixup+0x1c9/0x280 mm/mlock.c:549 > [<ffffffff81212ccc>] do_mlock+0x14c/0x180 mm/mlock.c:589 > [< inlined >] SYSC_munlock mm/mlock.c:651 > [<ffffffff812130b4>] SyS_munlock+0x74/0xb0 mm/mlock.c:643 > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > Locks held by T398: > #0 Lock 21b00c68 taken here: > [< inlined >] SYSC_munlock mm/mlock.c:650 > [<ffffffff8121308c>] SyS_munlock+0x4c/0xb0 mm/mlock.c:643 > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > #1 Lock bac2d750 taken here: > [< inlined >] i_mmap_lock_read include/linux/fs.h:509 > [< inlined >] rmap_walk_file mm/rmap.c:1533 > [<ffffffff8121e6e8>] rmap_walk+0x78/0x450 mm/rmap.c:1559 > [<ffffffff8121ef72>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > [<ffffffff81211bb0>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > [<ffffffff81212066>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > [<ffffffff812128a0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > [<ffffffff81212ac9>] mlock_fixup+0x1c9/0x280 mm/mlock.c:549 > [<ffffffff81212ccc>] do_mlock+0x14c/0x180 mm/mlock.c:589 > [< inlined >] SYSC_munlock mm/mlock.c:651 > [<ffffffff812130b4>] SyS_munlock+0x74/0xb0 mm/mlock.c:643 > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > #2 Lock 0895f570 taken here: > [< inlined >] spin_lock include/linux/spinlock.h:312 > [<ffffffff8121c959>] __page_check_address+0xd9/0x210 mm/rmap.c:681 > [< inlined >] page_check_address include/linux/rmap.h:204 > [<ffffffff8121d173>] try_to_unmap_one+0x53/0x4f0 mm/rmap.c:1198 > [< inlined >] rmap_walk_file mm/rmap.c:1540 > [<ffffffff8121e7b7>] rmap_walk+0x147/0x450 mm/rmap.c:1559 > [<ffffffff8121ef72>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > [<ffffffff81211bb0>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > [<ffffffff81212066>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > [<ffffffff812128a0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > [<ffffffff81212ac9>] mlock_fixup+0x1c9/0x280 mm/mlock.c:549 > [<ffffffff81212ccc>] do_mlock+0x14c/0x180 mm/mlock.c:589 > [< inlined >] SYSC_munlock mm/mlock.c:651 > [<ffffffff812130b4>] SyS_munlock+0x74/0xb0 mm/mlock.c:643 > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > DBG: addr: ffff880222610e10 > DBG: first offset: 0, second offset: 0 > DBG: T378 clock: {T378: 4486533, T398: 2405850} > DBG: T398 clock: {T398: 2406009} > ================================================================== > > ================================================================== > ThreadSanitizer: data-race in munlock_vma_pages_range > > Write of size 8 by thread T309 (K2577, CPU0): > [<ffffffff81211fc9>] munlock_vma_pages_range+0x59/0x3e0 mm/mlock.c:425 > [< inlined >] munlock_vma_pages_all mm/internal.h:252 > [<ffffffff81216cc3>] exit_mmap+0x163/0x190 mm/mmap.c:2824 > [<ffffffff81085685>] mmput+0x65/0x190 kernel/fork.c:708 > [< inlined >] exit_mm kernel/exit.c:437 > [<ffffffff8108c3a7>] do_exit+0x457/0x1420 kernel/exit.c:733 > [<ffffffff8108f08f>] do_group_exit+0x7f/0x140 kernel/exit.c:874 > [< inlined >] SYSC_exit_group kernel/exit.c:885 > [<ffffffff8108f170>] __wake_up_parent+0x0/0x50 kernel/exit.c:883 > [<ffffffff81eadb2e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > Locks held by T309: > > Previous read of size 8 by thread T293 (K2573, CPU3): > [<ffffffff8121cbe8>] try_to_unmap_one+0x78/0x4f0 mm/rmap.c:1208 > [< inlined >] rmap_walk_file mm/rmap.c:1540 > [<ffffffff8121e207>] rmap_walk+0x147/0x450 mm/rmap.c:1559 > [<ffffffff8121e9c2>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > [<ffffffff81211600>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > [<ffffffff81211ab6>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > [<ffffffff812122f0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > [< inlined >] munlock_vma_pages_all mm/internal.h:252 > [<ffffffff81216cc3>] exit_mmap+0x163/0x190 mm/mmap.c:2824 > [<ffffffff81085685>] mmput+0x65/0x190 kernel/fork.c:708 > [< inlined >] exit_mm kernel/exit.c:437 > [<ffffffff8108c3a7>] do_exit+0x457/0x1420 kernel/exit.c:733 > [<ffffffff8108f08f>] do_group_exit+0x7f/0x140 kernel/exit.c:874 > [< inlined >] SYSC_exit_group kernel/exit.c:885 > [<ffffffff8108f170>] __wake_up_parent+0x0/0x50 kernel/exit.c:883 > [<ffffffff81eadb2e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > Locks held by T293: > #0 Lock bb0dc710 taken here: > [< inlined >] i_mmap_lock_read include/linux/fs.h:509 > [< inlined >] rmap_walk_file mm/rmap.c:1533 > [<ffffffff8121e138>] rmap_walk+0x78/0x450 mm/rmap.c:1559 > [<ffffffff8121e9c2>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > [<ffffffff81211600>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > [<ffffffff81211ab6>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > [<ffffffff812122f0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > [< inlined >] munlock_vma_pages_all mm/internal.h:252 > [<ffffffff81216cc3>] exit_mmap+0x163/0x190 mm/mmap.c:2824 > [<ffffffff81085685>] mmput+0x65/0x190 kernel/fork.c:708 > [< inlined >] exit_mm kernel/exit.c:437 > [<ffffffff8108c3a7>] do_exit+0x457/0x1420 kernel/exit.c:733 > [<ffffffff8108f08f>] do_group_exit+0x7f/0x140 kernel/exit.c:874 > [< inlined >] SYSC_exit_group kernel/exit.c:885 > [<ffffffff8108f170>] __wake_up_parent+0x0/0x50 kernel/exit.c:883 > [<ffffffff81eadb2e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > #1 Lock 02e0f1b0 taken here: > [< inlined >] spin_lock include/linux/spinlock.h:312 > [<ffffffff8121c3a9>] __page_check_address+0xd9/0x210 mm/rmap.c:681 > [< inlined >] page_check_address include/linux/rmap.h:204 > [<ffffffff8121cbc3>] try_to_unmap_one+0x53/0x4f0 mm/rmap.c:1198 > [< inlined >] rmap_walk_file mm/rmap.c:1540 > [<ffffffff8121e207>] rmap_walk+0x147/0x450 mm/rmap.c:1559 > [<ffffffff8121e9c2>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > [<ffffffff81211600>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > [<ffffffff81211ab6>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > [<ffffffff812122f0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > [< inlined >] munlock_vma_pages_all mm/internal.h:252 > [<ffffffff81216cc3>] exit_mmap+0x163/0x190 mm/mmap.c:2824 > [<ffffffff81085685>] mmput+0x65/0x190 kernel/fork.c:708 > [< inlined >] exit_mm kernel/exit.c:437 > [<ffffffff8108c3a7>] do_exit+0x457/0x1420 kernel/exit.c:733 > [<ffffffff8108f08f>] do_group_exit+0x7f/0x140 kernel/exit.c:874 > [< inlined >] SYSC_exit_group kernel/exit.c:885 > [<ffffffff8108f170>] __wake_up_parent+0x0/0x50 kernel/exit.c:883 > [<ffffffff81eadb2e>] entry_SYSCALL_64_fastpath+0x12/0x71 > arch/x86/entry/entry_64.S:186 > > DBG: addr: ffff8800bb153a78 > DBG: first offset: 0, second offset: 0 > DBG: T309 clock: {T309: 1297809, T293: 747168} > DBG: T293 clock: {T293: 747528} > ================================================================== > > On Thu, Sep 10, 2015 at 10:36 AM, Kirill A. Shutemov > <kirill@xxxxxxxxxxxxx> wrote: > > On Wed, Sep 09, 2015 at 08:58:26PM -0400, Sasha Levin wrote: > >> On 09/07/2015 07:40 AM, Kirill A. Shutemov wrote: > >> > On Sun, Sep 06, 2015 at 03:21:05PM -0400, Sasha Levin wrote: > >> >> > ================================================================== > >> >> > ThreadSanitizer: data-race in munlock_vma_pages_range > >> >> > > >> >> > Write of size 8 by thread T378 (K2633, CPU3): > >> >> > [<ffffffff81212579>] munlock_vma_pages_range+0x59/0x3e0 mm/mlock.c:425 > >> >> > [<ffffffff81212ac9>] mlock_fixup+0x1c9/0x280 mm/mlock.c:549 > >> >> > [<ffffffff81212ccc>] do_mlock+0x14c/0x180 mm/mlock.c:589 > >> >> > [< inlined >] SyS_munlock+0x74/0xb0 SYSC_munlock mm/mlock.c:651 > >> >> > [<ffffffff812130b4>] SyS_munlock+0x74/0xb0 mm/mlock.c:643 > >> >> > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > >> >> > arch/x86/entry/entry_64.S:186 > >> > ... > >> > > >> >> > Previous read of size 8 by thread T398 (K2623, CPU2): > >> >> > [<ffffffff8121d198>] try_to_unmap_one+0x78/0x4f0 mm/rmap.c:1208 > >> >> > [< inlined >] rmap_walk+0x147/0x450 rmap_walk_file mm/rmap.c:1540 > >> >> > [<ffffffff8121e7b7>] rmap_walk+0x147/0x450 mm/rmap.c:1559 > >> >> > [<ffffffff8121ef72>] try_to_munlock+0xa2/0xc0 mm/rmap.c:1423 > >> >> > [<ffffffff81211bb0>] __munlock_isolated_page+0x30/0x60 mm/mlock.c:129 > >> >> > [<ffffffff81212066>] __munlock_pagevec+0x236/0x3f0 mm/mlock.c:331 > >> >> > [<ffffffff812128a0>] munlock_vma_pages_range+0x380/0x3e0 mm/mlock.c:476 > >> >> > [<ffffffff81212ac9>] mlock_fixup+0x1c9/0x280 mm/mlock.c:549 > >> >> > [<ffffffff81212ccc>] do_mlock+0x14c/0x180 mm/mlock.c:589 > >> >> > [< inlined >] SyS_munlock+0x74/0xb0 SYSC_munlock mm/mlock.c:651 > >> >> > [<ffffffff812130b4>] SyS_munlock+0x74/0xb0 mm/mlock.c:643 > >> >> > [<ffffffff81eb352e>] entry_SYSCALL_64_fastpath+0x12/0x71 > >> >> > arch/x86/entry/entry_64.S:186 > >> > Okay, the detected race is mlock/munlock vs. rmap. > >> > > >> > On rmap side we check vma->vm_flags in few places without taking > >> > vma->vm_mm->mmap_sem. The vma cannot be freed since we hold i_mmap_rwsem > >> > or anon_vma_lock, but nothing prevent vma->vm_flags from changing under > >> > us. > >> > > >> > In this particular case, speculative check in beginning of > >> > try_to_unmap_one() is fine, since we re-check it under mmap_sem later in > >> > the function. > >> > >> So you're suggesting that this isn't the cause of the bad page flags > >> error observed by Andrey and myself? > > > > I don't see it, but who knows. > > > > -- > > Kirill A. Shutemov -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>