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SubjectRe: [PATCH] f2fs: fix to relocate f2fs_balance_fs() in mkwrite()
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Hi Jaeguek,

On 2019/12/6 12:08, Jaegeuk Kim wrote:
> Hi Chao,
>
> I was testing this.
>
> https://github.com/jaegeuk/f2fs/commit/76be33b9f1fce70dd2d3f04f66d0f78b418fe3f5

The patch looks good.

BTW, do you mind adding below call stack into your patch? I guess it
describes this ABBA deadlock with more details. :)

Thanks,

>
> On 12/06, Chao Yu wrote:
>> As Dinosaur Huang reported, there is a potential deadlock in between
>> GC and mkwrite():
>>
>> Thread A Thread B
>> - do_page_mkwrite
>> - f2fs_vm_page_mkwrite
>> - lock_page
>> - f2fs_balance_fs
>> - mutex_lock(gc_mutex)
>> - f2fs_gc
>> - do_garbage_collect
>> - ra_data_block
>> - grab_cache_page
>> - f2fs_balance_fs
>> - mutex_lock(gc_mutex)
>>
>> In order to fix this, we just move f2fs_balance_fs() out of page lock's
>> coverage in f2fs_vm_page_mkwrite().
>>
>> Reported-by: Dinosaur Huang <dinosaur.huang@unisoc.com>
>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>> ---
>> fs/f2fs/file.c | 4 ++--
>> 1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>> index c0560d62dbee..ed3290225506 100644
>> --- a/fs/f2fs/file.c
>> +++ b/fs/f2fs/file.c
>> @@ -67,6 +67,8 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>>
>> f2fs_bug_on(sbi, f2fs_has_inline_data(inode));
>>
>> + f2fs_balance_fs(sbi, true);
>> +
>> file_update_time(vmf->vma->vm_file);
>> down_read(&F2FS_I(inode)->i_mmap_sem);
>> lock_page(page);
>> @@ -120,8 +122,6 @@ static vm_fault_t f2fs_vm_page_mkwrite(struct vm_fault *vmf)
>> out_sem:
>> up_read(&F2FS_I(inode)->i_mmap_sem);
>>
>> - f2fs_balance_fs(sbi, dn.node_changed);
>> -
>> sb_end_pagefault(inode->i_sb);
>> err:
>> return block_page_mkwrite_return(err);
>> --
>> 2.18.0.rc1
> .
>

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