On Wed, Jun 20, 2018 at 07:56:11AM -0700, Chris Mason wrote:
> During buffered writes, we follow this basic series of steps:
>
> again:
> lock all the pages
> wait for writeback on all the pages
> Take the extent range lock
> wait for ordered extents on the whole range
> clean all the pages
>
> if (copy_from_user_in_atomic() hits a fault) {
> drop our locks
> goto again;
> }
>
> dirty all the pages
> release all the locks
>
> The extra waiting, cleaning and locking are there to make sure we don't
> modify pages in flight to the drive, after they've been crc'd.
>
> If some of the pages in the range were already dirty when the write
> began, and we need to goto again, we create a window where a dirty page
> has been cleaned and unlocked. It may be reclaimed before we're able to
> lock it again, which means we'll read the old contents off the drive and
> lose any modifications that had been pending writeback.
>
> We don't actually need to clean the pages. All of the other locking in
> place makes sure we don't start IO on the pages, so we can just leave
> them dirty for the duration of the write.
>
> Fixes: 73d59314e6ed (the original btrfs merge)
> Signed-off-by: Chris Mason <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Moved from for-next to 4.20 queue.
