From f32f20e2bd1f3b83925f703704840eebb56faedb Mon Sep 17 00:00:00 2001 From: Tavian Barnes Date: Mon, 18 Mar 2024 09:56:54 -0400 Subject: btrfs: warn if EXTENT_BUFFER_UPTODATE is set while reading We recently tracked down a race condition that triggered a read for an extent buffer with EXTENT_BUFFER_UPTODATE already set. While this read was in progress, other concurrent readers would see the UPTODATE bit and return early as if the read was already complete, making accesses to the extent buffer conflict with the read operation that was overwriting it. Add a WARN_ON() to end_bbio_meta_read() for this situation to make similar races easier to spot in the future. Reviewed-by: Qu Wenruo Signed-off-by: Tavian Barnes Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/extent_io.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c index 23bdd05b5cec..ecb18a8db373 100644 --- a/fs/btrfs/extent_io.c +++ b/fs/btrfs/extent_io.c @@ -4275,6 +4275,13 @@ static void end_bbio_meta_read(struct btrfs_bio *bbio) struct folio_iter fi; u32 bio_offset = 0; + /* + * If the extent buffer is marked UPTODATE before the read operation + * completes, other calls to read_extent_buffer_pages() will return + * early without waiting for the read to finish, causing data races. + */ + WARN_ON(test_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags)); + eb->read_mirror = bbio->mirror_num; if (uptodate && -- cgit v1.2.3