Messages in this thread | | | Subject | Re: [PATCH] ext4: Fix i_disksize exceeding i_size problem in paritally written case | From | Zhihao Cheng <> | Date | Mon, 20 Mar 2023 20:49:07 +0800 |
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>> BTW, I want send another patch as follows: >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index bf0b7dea4900..570a687ae847 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file, >> return ext4_write_inline_data_end(inode, pos, len, copied, >> page); >> >> start = pos & (PAGE_SIZE - 1); >> - end = start + copied - 1; >> + end = start + (copied ? copied - 1 : copied); >> >> /* >> * Since we are holding inode lock, we are sure i_disksize <= >> @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file, >> * ext4_da_write_inline_data_end(). >> */ >> new_i_size = pos + copied; >> - if (copied && new_i_size > inode->i_size && >> + if (new_i_size > inode->i_size && >> ext4_da_should_update_i_disksize(page, end)) >> ext4_update_i_disksize(inode, new_i_size); >> >> This modification handle unconsistent i_size and i_disksize imported by >> ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()"). >> >> Paritially written may display a fake inode size for user, for example: >> >> >> >> i_disksize=1 >> >> generic_perform_write >> >> copied = iov_iter_copy_from_user_atomic(len) // copied = 0 >> >> ext4_da_write_end // skip updating i_disksize >> >> generic_write_end >> >> if (pos + copied > inode->i_size) { // 10 + 0 > 1, true >> >> i_size_write(inode, pos + copied); // i_size = 10 >> >> } >> >> >> >> 0 1 10 4096 >> >> |_|_______|_________..._____| >> >> | | >> >> i_size pos >> >> >> >> Now, user see the i_size is 10 (i_disksize is still 1). After inode >> >> destroyed, user will get the i_size is 1 read from disk. > > OK, but shouldn't we rather change generic_write_end() to not increase > i_size if no write happened? Because that is what seems somewhat > problematic... > > Honza >
After looking through some code, I find some other places have similar problem: 1. In ext4_write_end(), i_size is updated by ext4 not generic_write_end(). 2. The iommap framework, i_size is updated even copied is zero. 3. ubifs_write_end, i_size is updated even copied is zero.
It seems that fixing all places is not an easy work.
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