Re: [PATCH 0/2] btrfs: fixes for subpage which also affect read-only mount

On Mon, Mar 15, 2021 at 01:39:13PM +0800, Qu Wenruo wrote:

During the fstests run for btrfs subpage read-write support, generic/475
crashes the system with a very high chance.

It turns out the cause is also affecting btrfs subpage read-only mount
so it's worthy a quick fix.

Also the crash call site shows a new rabbit hole of hard coded
PAGE_SHIFT in readahead.

There's still a lot of PAGE_SHIFT use, not all of them are wrong but I
think we'll need to do an audit and categorize the valid uses, otherwise
it'll be a whack-a-mole.