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ext4: use private version of page_zero_new_buffers() for data=journal mode

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If there is a error while copying data from userspace into the page
cache during a write(2) system call, in data=journal mode, in
ext4_journalled_write_end() were using page_zero_new_buffers() from
fs/buffer.c.  Unfortunately, this sets the buffer dirty flag, which is
no good if journalling is enabled.  This is a long-standing bug that
goes back for years and years in ext3, but a combination of (a)
data=journal not being very common, (b) in many case it only results
in a warning message. and (c) only very rarely causes the kernel hang,
means that we only really noticed this as a problem when commit
998ef75ddb caused this failure to happen frequently enough to cause
generic/208 to fail when run in data=journal mode.

The fix is to have our own version of this function that doesn't call
mark_dirty_buffer(), since we will end up calling
ext4_handle_dirty_metadata() on the buffer head(s) in questions very
shortly afterwards in ext4_journalled_write_end().

Thanks to Dave Hansen and Linus Torvalds for helping to identify the
root cause of the problem.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.com>
This commit is contained in:
Theodore Ts'o 2015-10-15 10:29:05 -04:00
parent 36086d43f6
commit b90197b655
1 changed files with 33 additions and 1 deletions
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34
fs/ext4/inode.c
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@ -1181,6 +1181,38 @@ errout:
return ret ? ret : copied;
}
/*
* This is a private version of page_zero_new_buffers() which doesn't
* set the buffer to be dirty, since in data=journalled mode we need
* to call ext4_handle_dirty_metadata() instead.
*/
static void zero_new_buffers(struct page *page, unsigned from, unsigned to)
{
unsigned int block_start = 0, block_end;
struct buffer_head *head, *bh;
bh = head = page_buffers(page);
do {
block_end = block_start + bh->b_size;
if (buffer_new(bh)) {
if (block_end > from && block_start < to) {
if (!PageUptodate(page)) {
unsigned start, size;
start = max(from, block_start);
size = min(to, block_end) - start;
zero_user(page, start, size);
set_buffer_uptodate(bh);
}
clear_buffer_new(bh);
}
}
block_start = block_end;
bh = bh->b_this_page;
} while (bh != head);
}
static int ext4_journalled_write_end(struct file *file,
struct address_space *mapping,
loff_t pos, unsigned len, unsigned copied,
@ -1207,7 +1239,7 @@ static int ext4_journalled_write_end(struct file *file,
if (copied < len) {
if (!PageUptodate(page))
copied = 0;
page_zero_new_buffers(page, from+copied, to);
zero_new_buffers(page, from+copied, to);
}
ret = ext4_walk_page_buffers(handle, page_buffers(page), from,