[PATCH] bcachefs: no console_lock in bch2_print_string_as_lines

[John Ogness]

On 2024-07-10, Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
> console_lock is the outermost subsystem lock for a lot of subsystems,
> which means get/put_user must nest within. Which means it cannot be
> acquired somewhere deeply nested in other locks, and most definitely
> not while holding fs locks potentially needed to resolve faults.
>
> console_trylock is the best we can do here. But John pointed out on a
> previous version that this is futile:
>
> "Using the console lock here at all is wrong. The console lock does not
> prevent other CPUs from calling printk() and inserting lines in between.
>
> "There is no way to guarantee a contiguous ringbuffer block using
> multiple printk() calls.
>
> "The console_lock usage should be removed."
>
> https://lore.kernel.org/lkml/87frsh33xp.fsf@jogness.linutronix.de/
>
> Do that.

Note that there is more of this incorrect usage of console lock in:

fs/bcachefs/debug.c:bch2_btree_verify_replica()

fs/bcachefs/bset.c:bch2_dump_btree_node()

from commit 1c6fdbd8f246("bcachefs: Initial commit")

... and its parent bcache:

drivers/md/bcache/debug.c:bch_btree_verify()

drivers/md/bcache/bset.c:bch_dump_bucket()

from commit cafe56359144("bcache: A block layer cache")

These should also be removed. Although Kent should verify that the
console lock is not providing some sort of necessary side-effect
synchronization.

John Ogness