Re: [PATCH] mm: list_lru: Fix NULL pointer dereference in list_lru_add()

[Kent Overstreet]

On Fri, Jul 12, 2024 at 12:28:57PM GMT, Youling Tang wrote:
> Hi, Kent
> 
> On 12/07/2024 12:07, Kent Overstreet wrote:
> > On Fri, Jul 12, 2024 at 11:25:54AM GMT, Youling Tang wrote:
> > > From: Youling Tang <tangyouling@xxxxxxxxxx>
> > > 
> > > Note that list_lru_from_memcg_idx() may return NULL, so it is necessary
> > > to error handle the return value to avoid triggering NULL pointer
> > > dereference BUG.
> > > 
> > > The issue was triggered for discussion [1],
> > > Link [1]: https://lore.kernel.org/linux-bcachefs/84de6cb1-57bd-42f7-8029-4203820ef0b4@xxxxxxxxx/T/#m901bb26cdb1d9d4bacebf0d034f0a5a712cc93a6
> > I see no explanation for why this is the correct fix, and I doubt it is.
> > What's the real reason for the NULL lru_list_one, and why doesn't this
> > come up on other filesystems?
> We can break it down into two questions (independent of each other):
> 1) Error handling is necessary when l (lru_list_one) is NULL here.

No, you're just hiding the actual bug - since I wasn't clear, I'm naking
this patch.