Re: [RFC v5 05/11] mm: fix lock dependency against mapping->i_mmap_rwsem

[Laurent Dufour]

On 08/08/2017 13:17, Anshuman Khandual wrote:
> On 06/16/2017 11:22 PM, Laurent Dufour wrote:
>> kworker/32:1/819 is trying to acquire lock:
>>  (&vma->vm_sequence){+.+...}, at: [<c0000000002f20e0>]
>> zap_page_range_single+0xd0/0x1a0
>>
>> but task is already holding lock:
>>  (&mapping->i_mmap_rwsem){++++..}, at: [<c0000000002f229c>]
>> unmap_mapping_range+0x7c/0x160
>>
>> which lock already depends on the new lock.
>>
>> the existing dependency chain (in reverse order) is:
>>
>> -> #2 (&mapping->i_mmap_rwsem){++++..}:
>>        down_write+0x84/0x130
>>        __vma_adjust+0x1f4/0xa80
>>        __split_vma.isra.2+0x174/0x290
>>        do_munmap+0x13c/0x4e0
>>        vm_munmap+0x64/0xb0
>>        elf_map+0x11c/0x130
>>        load_elf_binary+0x6f0/0x15f0
>>        search_binary_handler+0xe0/0x2a0
>>        do_execveat_common.isra.14+0x7fc/0xbe0
>>        call_usermodehelper_exec_async+0x14c/0x1d0
>>        ret_from_kernel_thread+0x5c/0x68
>>
>> -> #1 (&vma->vm_sequence/1){+.+...}:
>>        __vma_adjust+0x124/0xa80
>>        __split_vma.isra.2+0x174/0x290
>>        do_munmap+0x13c/0x4e0
>>        vm_munmap+0x64/0xb0
>>        elf_map+0x11c/0x130
>>        load_elf_binary+0x6f0/0x15f0
>>        search_binary_handler+0xe0/0x2a0
>>        do_execveat_common.isra.14+0x7fc/0xbe0
>>        call_usermodehelper_exec_async+0x14c/0x1d0
>>        ret_from_kernel_thread+0x5c/0x68
>>
>> -> #0 (&vma->vm_sequence){+.+...}:
>>        lock_acquire+0xf4/0x310
>>        unmap_page_range+0xcc/0xfa0
>>        zap_page_range_single+0xd0/0x1a0
>>        unmap_mapping_range+0x138/0x160
>>        truncate_pagecache+0x50/0xa0
>>        put_aio_ring_file+0x48/0xb0
>>        aio_free_ring+0x40/0x1b0
>>        free_ioctx+0x38/0xc0
>>        process_one_work+0x2cc/0x8a0
>>        worker_thread+0xac/0x580
>>        kthread+0x164/0x1b0
>>        ret_from_kernel_thread+0x5c/0x68
>>
>> other info that might help us debug this:
>>
>> Chain exists of:
>>   &vma->vm_sequence --> &vma->vm_sequence/1 --> &mapping->i_mmap_rwsem
>>
>>  Possible unsafe locking scenario:
>>
>>        CPU0                    CPU1
>>        ----                    ----
>>   lock(&mapping->i_mmap_rwsem);
>>                                lock(&vma->vm_sequence/1);
>>                                lock(&mapping->i_mmap_rwsem);
>>   lock(&vma->vm_sequence);
>>
>>  *** DEADLOCK ***
>>
>> To fix that we must grab the vm_sequence lock after any mapping one in
>> __vma_adjust().
>>
>> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
> 
> Should not this be folded back into the previous patch ? It fixes an
> issue introduced by the previous one.

This is an option, but the previous one was signed by Peter, and I'd prefer
to keep his unchanged and add this new one to fix that.
Again this is to ease the review.