[PATCH v2 08/26] btrfs: handle errors properly inside btrfs_submit_compressed_read()

Qu Wenruo
2021-08-29T05:25:16Z

There are quite some BUG_ON()s inside btrfs_submit_compressed_read(),
namingly all errors inside the for() loop relies on BUG_ON() to handle
-ENOMEM.

Handle these errors properly by:

- Wait for submitted bios to finish first
Using wake_var_event() APIs to wait without introducing extra memory
overhead inside compressed_bio.
This allows us to wait for any submitted bio to finish, while still
keeps the compressed_bio from being freed.

- Introduce finish_compressed_bio_read() to finish the compressed_bio

- Properly end the bio and finish compressed_bio when error happens

Now in btrfs_submit_compressed_read() even when the bio submission
failed, we can properly handle the error without triggering BUG_ON().

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
fs/btrfs/compression.c | 133 +++++++++++++++++++++++++----------------
1 file changed, 83 insertions(+), 50 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 79379fa741b8..d4b46d46b249 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -223,9 +223,60 @@ static bool dec_and_test_compressed_bio(struct compressed_bio *cb,
last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
&cb->pending_sectors);
atomic_dec(&cb->pending_bios);
+ /*
+ * Here we must wake up the possible error handler after all other
+ * operations on @cb finished, or we can race with
+ * finish_compressed_bio_*() which may free @cb.
+ */
+ wake_up_var(cb);
+
return last_io;
}

+static void finish_compressed_bio_read(struct compressed_bio *cb,
+ struct bio *bio)
+{
+ unsigned int index;
+ struct page *page;
+
+ /* Release the compressed pages */
+ for (index = 0; index < cb->nr_pages; index++) {
+ page = cb->compressed_pages[index];
+ page->mapping = NULL;
+ put_page(page);
+ }
+
+ /* Do io completion on the original bio */
+ if (cb->errors) {
+ bio_io_error(cb->orig_bio);
+ } else {
+ struct bio_vec *bvec;
+ struct bvec_iter_all iter_all;
+
+ ASSERT(bio);
+ ASSERT(!bio->bi_status);
+ /*
+ * We have verified the checksum already, set page
+ * checked so the end_io handlers know about it
+ */
+ ASSERT(!bio_flagged(bio, BIO_CLONED));
+ bio_for_each_segment_all(bvec, cb->orig_bio, iter_all) {
+ u64 bvec_start = page_offset(bvec->bv_page) +
+ bvec->bv_offset;
+
+ btrfs_page_set_checked(btrfs_sb(cb->inode->i_sb),
+ bvec->bv_page, bvec_start,
+ bvec->bv_len);
+ }
+
+ bio_endio(cb->orig_bio);
+ }
+
+ /* Finally free the cb struct */
+ kfree(cb->compressed_pages);
+ kfree(cb);
+}
+
/* when we finish reading compressed pages from the disk, we
* decompress them and then run the bio end_io routines on the
* decompressed pages (in the inode address space).
@@ -240,8 +291,6 @@ static void end_compressed_bio_read(struct bio *bio)
{
struct compressed_bio *cb = bio->bi_private;
struct inode *inode;
- struct page *page;
- unsigned int index;
unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
int ret = 0;

@@ -276,42 +325,7 @@ static void end_compressed_bio_read(struct bio *bio)
csum_failed:
if (ret)
cb->errors = 1;
-
- /* release the compressed pages */
- index = 0;
- for (index = 0; index < cb->nr_pages; index++) {
- page = cb->compressed_pages[index];
- page->mapping = NULL;
- put_page(page);
- }
-
- /* do io completion on the original bio */
- if (cb->errors) {
- bio_io_error(cb->orig_bio);
- } else {
- struct bio_vec *bvec;
- struct bvec_iter_all iter_all;
-
- /*
- * we have verified the checksum already, set page
- * checked so the end_io handlers know about it
- */
- ASSERT(!bio_flagged(bio, BIO_CLONED));
- bio_for_each_segment_all(bvec, cb->orig_bio, iter_all) {
- u64 bvec_start = page_offset(bvec->bv_page) +
- bvec->bv_offset;
-
- btrfs_page_set_checked(btrfs_sb(cb->inode->i_sb),
- bvec->bv_page, bvec_start,
- bvec->bv_len);
- }
-
- bio_endio(cb->orig_bio);
- }
-
- /* finally free the cb struct */
- kfree(cb->compressed_pages);
- kfree(cb);
+ finish_compressed_bio_read(cb, bio);
out:
bio_put(bio);
}
@@ -834,20 +848,20 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
BTRFS_WQ_ENDIO_DATA);
- BUG_ON(ret); /* -ENOMEM */
+ if (ret)
+ goto finish_cb;

ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
- BUG_ON(ret); /* -ENOMEM */
+ if (ret)
+ goto finish_cb;

nr_sectors = DIV_ROUND_UP(comp_bio->bi_iter.bi_size,
fs_info->sectorsize);
sums += fs_info->csum_size * nr_sectors;

ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
- if (ret) {
- comp_bio->bi_status = ret;
- bio_endio(comp_bio);
- }
+ if (ret)
+ goto finish_cb;

comp_bio = btrfs_bio_alloc(cur_disk_byte);
comp_bio->bi_opf = REQ_OP_READ;
@@ -861,16 +875,16 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,

atomic_inc(&cb->pending_bios);
ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
- BUG_ON(ret); /* -ENOMEM */
+ if (ret)
+ goto last_bio;

ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
- BUG_ON(ret); /* -ENOMEM */
+ if (ret)
+ goto last_bio;

ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
- if (ret) {
- comp_bio->bi_status = ret;
- bio_endio(comp_bio);
- }
+ if (ret)
+ goto last_bio;

return 0;

@@ -886,6 +900,25 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
out:
free_extent_map(em);
return ret;
+last_bio:
+ comp_bio->bi_status = ret;
+ /* This is the last bio, endio functions will free @cb */
+ bio_endio(comp_bio);
+ return ret;
+finish_cb:
+ if (comp_bio) {
+ comp_bio->bi_status = ret;
+ bio_endio(comp_bio);
+ }
+ wait_var_event(cb, atomic_read(&cb->pending_bios) == 0);
+ /*
+ * Even with previous bio ended, we should still have io not yet
+ * submitted, thus need to finish @cb manually.
+ */
+ ASSERT(refcount_read(&cb->pending_sectors));
+ /* Now we are the only one referring @cb, can finish it safely. */
+ finish_compressed_bio_read(cb, NULL);
+ return ret;
}

/*
--
2.32.0