6.1-stable review patch. If anyone has any objections, please let me know.
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From: Qu Wenruo wqu@suse.com
[ 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: 0528476b6ac7 ("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 --- fs/btrfs/file.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index 9e06d1a0d373d..3814f09dc4ae0 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2224,15 +2224,20 @@ static void btrfs_punch_hole_lock_range(struct inode *inode, * will always return true. * So here we need to do extra page alignment for * filemap_range_has_page(). + * + * And do not decrease page_lockend right now, as it can be 0. */ const u64 page_lockstart = round_up(lockstart, PAGE_SIZE); - const u64 page_lockend = round_down(lockend + 1, PAGE_SIZE) - 1; + const u64 page_lockend = round_down(lockend + 1, PAGE_SIZE);
while (1) { truncate_pagecache_range(inode, lockstart, lockend);
lock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend, cached_state); + /* The same page or adjacent pages. */ + if (page_lockend <= page_lockstart) + break; /* * We can't have ordered extents in the range, nor dirty/writeback * pages, because we have locked the inode's VFS lock in exclusive @@ -2244,7 +2249,7 @@ static void btrfs_punch_hole_lock_range(struct inode *inode, * we do, unlock the range and retry. */ if (!filemap_range_has_page(inode->i_mapping, page_lockstart, - page_lockend)) + page_lockend - 1)) break;
unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend,