From 4d89d377bbb0e34cd1571b57a984c2326cab69b5 Mon Sep 17 00:00:00 2001 From: Jeff Mahoney Date: Mon, 15 Jun 2015 09:41:15 -0400 Subject: [PATCH] btrfs: btrfs_issue_discard ensure offset/length are aligned to sector boundaries It's possible, though unexpected, to pass unaligned offsets and lengths to btrfs_issue_discard. We then shift the offset/length values to sector units. If an unaligned offset has been passed, it will result in the entire sector being discarded, possibly losing data. An unaligned length is safe but we'll end up returning an inaccurate number of discarded bytes. This patch aligns the offset to the 512B boundary, adjusts the length, and warns, since we shouldn't be discarding on an offset that isn't aligned with our sector size. Signed-off-by: Jeff Mahoney Reviewed-by: Filipe Manana Tested-by: Filipe Manana Signed-off-by: Chris Mason --- fs/btrfs/extent-tree.c | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 16655bb5f293..7aa6ad1f014d 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -1887,12 +1887,21 @@ static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len, u64 *discarded_bytes) { int ret = 0; + u64 aligned_start = ALIGN(start, 1 << 9); + + if (WARN_ON(start != aligned_start)) { + len -= aligned_start - start; + len = round_down(len, 1 << 9); + start = aligned_start; + } *discarded_bytes = 0; - ret = blkdev_issue_discard(bdev, start >> 9, len >> 9, GFP_NOFS, 0); - if (!ret) - *discarded_bytes = len; - + if (len) { + ret = blkdev_issue_discard(bdev, start >> 9, len >> 9, + GFP_NOFS, 0); + if (!ret) + *discarded_bytes = len; + } return ret; }