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SubjectRe: [PATCH 3/4] f2fs: fix avoid race between truncate and background GC
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On 2018/7/29 14:13, Jaegeuk Kim wrote:
> On 07/29, Chao Yu wrote:
>> On 2018/7/29 9:58, Jaegeuk Kim wrote:
>>> On 07/27, Chao Yu wrote:
>>>> Thread A Background GC
>>>> - f2fs_setattr isize to 0
>>>> - truncate_setsize
>>>> - gc_data_segment
>>>> - f2fs_get_read_data_page page #0
>>>> - set_page_dirty
>>>> - set_cold_data
>>>> - f2fs_truncate
>>>>
>>>> - f2fs_setattr isize to 4k
>>>> - read 4k <--- hit data in cached page #0
>>>>
>>>> Above race condition can cause read out invalid data in a truncated
>>>> page, fix it by i_gc_rwsem[WRITE] lock.
>>>
>>> We can truncate pages again after f2fs_truncate()?
>>
>> I think it can fix this issue, although it looks a little strange to truncate
>> page cache twice.
>
> It'd be fine to do setsize first, and drop the cache later.

Let me rethink about this solution, since we have different case like punch_hole
which may not need setsize.

Thanks,

>
>>
>> Thanks,
>>
>>>
>>>>
>>>> Signed-off-by: Chao Yu <yuchao0@huawei.com>
>>>> ---
>>>> fs/f2fs/data.c | 4 ++++
>>>> fs/f2fs/file.c | 33 +++++++++++++++++++--------------
>>>> 2 files changed, 23 insertions(+), 14 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>>> index 071224ded5f4..a29f3162b887 100644
>>>> --- a/fs/f2fs/data.c
>>>> +++ b/fs/f2fs/data.c
>>>> @@ -2214,10 +2214,14 @@ static void f2fs_write_failed(struct address_space *mapping, loff_t to)
>>>> loff_t i_size = i_size_read(inode);
>>>>
>>>> if (to > i_size) {
>>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +
>>>> truncate_pagecache(inode, i_size);
>>>> f2fs_truncate_blocks(inode, i_size, true);
>>>> +
>>>> up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> }
>>>> }
>>>>
>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>>> index 7bd2412a8c37..ed5c9b0e0d0c 100644
>>>> --- a/fs/f2fs/file.c
>>>> +++ b/fs/f2fs/file.c
>>>> @@ -796,22 +796,25 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
>>>> }
>>>>
>>>> if (attr->ia_valid & ATTR_SIZE) {
>>>> - if (attr->ia_size <= i_size_read(inode)) {
>>>> - down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> - truncate_setsize(inode, attr->ia_size);
>>>> + bool to_smaller = (attr->ia_size <= i_size_read(inode));
>>>> +
>>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> + down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> +
>>>> + truncate_setsize(inode, attr->ia_size);
>>>> +
>>>> + if (to_smaller)
>>>> err = f2fs_truncate(inode);
>>>> - up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> - if (err)
>>>> - return err;
>>>> - } else {
>>>> - /*
>>>> - * do not trim all blocks after i_size if target size is
>>>> - * larger than i_size.
>>>> - */
>>>> - down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> - truncate_setsize(inode, attr->ia_size);
>>>> - up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> + /*
>>>> + * do not trim all blocks after i_size if target size is
>>>> + * larger than i_size.
>>>> + */
>>>> + up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> + if (err)
>>>> + return err;
>>>>
>>>> + if (!to_smaller) {
>>>> /* should convert inline inode here */
>>>> if (!f2fs_may_inline_data(inode)) {
>>>> err = f2fs_convert_inline_inode(inode);
>>>> @@ -958,6 +961,7 @@ static int punch_hole(struct inode *inode, loff_t offset, loff_t len)
>>>>
>>>> blk_start = (loff_t)pg_start << PAGE_SHIFT;
>>>> blk_end = (loff_t)pg_end << PAGE_SHIFT;
>>>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> down_write(&F2FS_I(inode)->i_mmap_sem);
>>>> truncate_inode_pages_range(mapping, blk_start,
>>>> blk_end - 1);
>>>> @@ -966,6 +970,7 @@ static int punch_hole(struct inode *inode, loff_t offset, loff_t len)
>>>> ret = f2fs_truncate_hole(inode, pg_start, pg_end);
>>>> f2fs_unlock_op(sbi);
>>>> up_write(&F2FS_I(inode)->i_mmap_sem);
>>>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>>> }
>>>> }
>>>>
>>>> --
>>>> 2.18.0.rc1

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