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