[ Upstream commit bc2dbc4983afedd198490cca043798f57c93e9bf ]
[BUG]
When running btrfs/004 with 4K fs block size and 64K page size,
sometimes fsstress workload can take 100% CPU for a while, but not long
enough to trigger a 120s hang warning.
[CAUSE]
When such 100% CPU usage happens, btrfs_punch_hole_lock_range() is
always in the call trace.
One example when this problem happens, the function
btrfs_punch_hole_lock_range() got the following parameters:
lock_start = 4096, lockend = 20469
Then we calculate @page_lockstart by rounding up lock_start to page
boundary, which is 64K (page size is 64K).
For @page_lockend, we round down the value towards page boundary, which
result 0. Then since we need to pass an inclusive end to
filemap_range_has_page(), we subtract 1 from the rounded down value,
resulting in (u64)-1.
In the above case, the range is inside the same page, and we do not even
need to call filemap_range_has_page(), not to mention to call it with
(u64)-1 at the end.
This behavior will cause btrfs_punch_hole_lock_range() to busy loop
waiting for irrelevant range to have its pages dropped.
[FIX]
Calculate @page_lockend by just rounding down @lockend, without
decreasing the value by one. So @page_lockend will no longer overflow.
Then exit early if @page_lockend is no larger than @page_lockstart.
As it means either the range is inside the same page, or the two pages
are adjacent already.
Finally only decrease @page_lockend when calling filemap_range_has_page().
Fixes: 0528476b6a ("btrfs: fix the filemap_range_has_page() call in btrfs_punch_hole_lock_range()")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
4a1b61f910