On Thu, Nov 9, 2017 at 1:49 PM, <jglisse@xxxxxxxxxx> wrote:
>
> (Result of code inspection only, i do not have a bug, nor know a bug
> that would be explain by this issue. Is there a kernel trace database
> one can query for that ?)
This is intentional.
See the comment above the code you added:
* Be careful: the buffer linked list is a NULL terminated one, rather
* than the circular one we're used to.
and then nobh_write_end() does:
struct buffer_head *head = fsdata;
...
while (head) {
bh = head;
head = head->b_this_page;
free_buffer_head(bh);
}
so it *depends* on the bh list being NULL-terminated.
So your patch is definitely wrong and breaks that nobh_write_end() case.
Which is not to say that there couldn't be a NULL pointer dereference
in some error path exactly because this code intentionally breaks the
normal rules.
But no, I'm definitely not applying this patch as-is, and not just before 4.14.
Linus