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

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2021/3/15 下午11:42, David Sterba wrote:
> 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.
>

Already did that.

The current valid use case for PAGE_SHIFT are:
- Grab page
   Including:
   * compression
   * raid56
   * relocation
   * buffered write in file.c
   * sb cross page check in volumes.c
   * send
   * zoned
   * sb rw in disk-io.c
   * tree csum in disk-io.c
   * free space cache v1
- Some legacy code still runs in full page mode
   Including:
   * defrag

- Verification code
   That part has way more hardcoded part to be addressed.
   Will be addressed in the final part, along with selftest enhancement.

Although there can be something missing, I believe it shouldn't be that
hard to hit during fstests then.

Thanks,
Qu