Ahead of the imminent Linux 6.19-rc5 release, the char/misc pull request was merged earlier today with a notable fix to the Rust Binder driver as well as adding the Intel Nova Lake Point S device ID to the MEI driver.

Today’s char/misc merge brings a fix for the Rust Binder driver. Google’s Rust Binder driver debuted in the upstream Linux 6.18 kernel as an alternative to the existing C-based Binder driver in the kernel used by Android.

That Rust Binder driver led to the first CVE being assigned to the kernel’s Rust code. Now there is another fix to the Rust Binder driver due to a mishap when updating the Rust Binder driver for its Linux 6.18 mainlining.

Alice Ryhl of Google explained in the patch last month:

"When forward-porting Rust Binder to 6.18, I neglected to take commit fb56fdf8b9a2 ("mm/list_lru: split the lock to per-cgroup scope") into account, and apparently I did not end up running the shrinker callback when I sanity tested the driver before submission. This leads to crashes like the following:

============================================ WARNING: possible recursive locking detected 6.18.0-mainline-maybe-dirty #1 Tainted: G IO

kswapd0/68 is trying to acquire lock: ffff956000fa18b0 (&l->lock){+.+.}-{2:2}, at: lock_list_lru_of_memcg+0x128/0x230

but task is already holding lock: ffff956000fa18b0 (&l->lock){+.+.}-{2:2}, at: rust_helper_spin_lock+0xd/0x20

other info that might help us debug this: Possible unsafe locking scenario:

CPU0

lock(&l->lock); lock(&l->lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by kswapd0/68: #0: ffffffff90d2e260 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0x597/0x1160 #1: ffff956000fa18b0 (&l->lock){+.+.}-{2:2}, at: rust_helper_spin_lock+0xd/0x20 #2: ffffffff90cf3680 (rcu_read_lock){....}-{1:2}, at: lock_list_lru_of_memcg+0x2d/0x230

To fix this, remove the spin_lock() call from rust_shrink_free_page()."

Dropping one (unsafe) line of Rust code avoids this crash. The patch is merged today for Linux 6.19-rc5 and is also marked for back-porting to the stable Linux 6.19 kernel.

The other notable bit with today’s char/misc pull is adding Nova Lake S support to the Intel Management Engine Interface "MEI" driver. As it’s just a new device ID and no other driver changes needed, it’s fine for this late-stage of the Linux 6.19 cycle as it doesn’t risk regressing existing hardware support.