Btrfs: don't clean dirty pages during buffered writes
commit 7703bdd8d23e6ef057af3253958a793ec6066b28 upstream. 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: 73d59314 (the original btrfs merge) CC: stable@vger.kernel.org # v4.4+ Signed-off-by: NChris Mason <clm@fb.com> Reviewed-by: NDavid Sterba <dsterba@suse.com> Signed-off-by: NDavid Sterba <dsterba@suse.com> Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
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