Hi,
you're right. thanks for the patch.
thanks, Alex
>>>>> sho (s) writes:
s> Hi Alex
s> I found a bug on linux-2.6.19-rc6 with Alex's patches.
s> With no files on the device, doing the following system call:
s> 1. open with O_CREAT
s> fd = open("test_file", O_RDWR|O_CREAT, 0777)
s> 2. ftruncate (length is not aligned with blocksize)
s> ftruncate(fd, 200)
s> 3. write out the same block
s> write(fd, write_buf, 100)
s> As a result, panic occurred at the following code:
s> ext4_wb_commit_write()
s> BUG_ON(EXT4_I(inode)->i_locality_group == NULL);
s> I tracked down the scenario of causing this panic, which is as below:
s> 1. i_locality_group is set to NULL when a file is created at first
s> 2. Given a length which is not aligned with blocksize to ftruncate,
s> PG_dirty flag is set in _set_page_dirty_nobuffers() after zeroing
s> out halfway part of the block on ftruncate
s> ext4_wb_block_truncate_page()
s> kaddr = kmap_atomic(page, KM_USER0);
s> memset(kaddr + offset, 0, length);
s> flush_dcache_page(page);
s> kunmap_atomic(kaddr, KM_USER0);
s> SetPageUptodate(page);s
s> _set_page_dirty_nobuffers(page);
s> 3. With PG_dirty flag set, i_locality_group is not set in
s> ext4_lg_page_enter_inode()
s> ext4_wb_commit_write()
s> if (__set_page_dirty_nobuffers(page))
s> ext4_lg_page_enter_inode(inode, page,
s> PageMappedToDisk(page));
s> 4. i_locality_group set to NULL causes BUG_ON
s> I tried the attached patch where ext4_lg_page_enter_inode()
s> is necessarily called. It seems to me that the problem does not occur
s> with this patch, how about your comment?
s> diff -upNr -X linux-2.6.19-rc6/Documentation/dontdiff linux-2.6.19-rc6/fs/ext4/writeback.c linux-2.6.19-rc6-tmp/fs/ext4/writeback.c
s> --- linux-2.6.19-rc6/fs/ext4/writeback.c 2006-12-22 19:16:17.000000000 +0900
s> +++ linux-2.6.19-rc6-tmp/fs/ext4/writeback.c 2006-12-22 19:15:45.000000000 +0900
s> @@ -968,10 +968,8 @@ int ext4_wb_commit_write(struct file *fi
s> - if (__set_page_dirty_nobuffers(page)) {
s> - __set_page_dirty_nobuffers(page);
s> - ext4_lg_page_enter_inode(inode, page, PageMappedToDisk(page));
s> - }
s> + __set_page_dirty_nobuffers(page);
s> + ext4_lg_page_enter_inode(inode, page, PageMappedToDisk(page));
s> Cheers, Takashi
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