On Tue, Jul 16, 2024 at 10:28:33AM GMT, Youling Tang wrote: > Hi, Kent > > On 12/07/2024 23:49, Kent Overstreet wrote: > > 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. > We should use kmem_cache_alloc_lru() instead of kmem_cache_alloc(), > similar to the [1] modification. > > Apply the following patch to fix the problem: Thanks, send it as a proper patch and I'll apply it > > diff --git a/fs/bcachefs/fs.c b/fs/bcachefs/fs.c > index f9c9a95d7d4c..79a580dfb5e1 100644 > --- a/fs/bcachefs/fs.c > +++ b/fs/bcachefs/fs.c > @@ -227,7 +227,8 @@ static struct inode *bch2_alloc_inode(struct super_block > *sb) > > static struct bch_inode_info *__bch2_new_inode(struct bch_fs *c) > { > - struct bch_inode_info *inode = kmem_cache_alloc(bch2_inode_cache, > GFP_NOFS); > + struct bch_inode_info *inode = alloc_inode_sb(c->vfs_sb, > bch2_inode_cache, GFP_NOFS); > if (!inode) > return NULL; > > Link [1]: https://lwn.net/ml/linux-kernel/20220228122126.37293-5-songmuchun@xxxxxxxxxxxxx/ > > Thanks, > Youling.
