Re: [PATCH] btrfs: scrub: skip PREALLOC extents on RAID stripe-tree

From: Qu Wenruo
Date: Thu Sep 12 2024 - 17:33:04 EST




在 2024/9/13 00:03, Johannes Thumshirn 写道:
From: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>

When scrubbing a RAID stripe-tree based filesystem with preallocated
extents, the btrfs_map_block() called by
scrub_submit_extent_sector_read() will return ENOENT, because there is
no RAID stripe-tree entry for preallocated extents. This then causes
the sector to be marked as a sector with an I/O error.

To prevent this false alert don't mark secotors for that
btrfs_map_block() returned an ENOENT as I/O errors but skip them.

This results for example in errors in fstests' btrfs/060 .. btrfs/074
which all perform fsstress and scrub operations. Whit this fix, these
errors are gone and the tests pass again.

Cc: Qu Wenru <wqu@xxxxxxxx>

My concern is, ENOENT can be some real problems other than PREALLOC.
I'd prefer this to be the last-resort method.

Would it be possible to create an RST entry for preallocated operations
manually? E.g. without creating a dummy OE, but just insert the needed
RST entries into RST tree at fallocate time?

Thanks,
Qu

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
---
fs/btrfs/scrub.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 3a3427428074..b195c41676e3 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1657,7 +1657,7 @@ static u32 stripe_length(const struct scrub_stripe *stripe)
}

static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
- struct scrub_stripe *stripe)
+ struct scrub_stripe *stripe)
{
struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
struct btrfs_bio *bbio = NULL;
@@ -1703,10 +1703,21 @@ static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
err = btrfs_map_block(fs_info, BTRFS_MAP_READ, logical,
&stripe_len, &bioc, &io_stripe, &mirror);
btrfs_put_bioc(bioc);
- if (err < 0) {
+ if (err < 0 && err != -ENOENT) {
set_bit(i, &stripe->io_error_bitmap);
set_bit(i, &stripe->error_bitmap);
continue;
+ } else if (err == -ENOENT) {
+ /*
+ * btrfs_map_block() returns -ENOENT if it can't
+ * find the logical address in the RAID stripe
+ * tree. This can happens on PREALLOC extents.
+ * As we know the extent tree has an extent
+ * recorded there, we can be sure this is a
+ * PREALLOC extent, so skip this sector and
+ * continue to the next.
+ */
+ continue;
}

bbio = btrfs_bio_alloc(stripe->nr_sectors, REQ_OP_READ,