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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 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.

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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