On 4/15/21 1:04 AM, Qu Wenruo wrote:
The new function, end_bio_subpage_eb_writepage(), will handle the
metadata writeback endio.
The major differences involved are:
- How to grab extent buffer
Now page::private is a pointer to btrfs_subpage, we can no longer grab
extent buffer directly.
Thus we need to use the bv_offset to locate the extent buffer manually
and iterate through the whole range.
- Use btrfs_subpage_end_writeback() caller
This helper will handle the subpage writeback for us.
Since this function is executed under endio context, when grabbing
extent buffers it can't grab eb->refs_lock as that lock is not designed
to be grabbed under hardirq context.
So here introduce a helper, find_extent_buffer_nospinlock(), for such
situation, and convert find_extent_buffer() to use that helper.
Signed-off-by: Qu Wenruo <w...@suse.com>
---
fs/btrfs/extent_io.c | 135 +++++++++++++++++++++++++++++++++----------
1 file changed, 106 insertions(+), 29 deletions(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index a50adbd8808d..21a14b1cb065 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4080,13 +4080,97 @@ static void set_btree_ioerr(struct page *page, struct
extent_buffer *eb)
}
}
+/*
+ * This is the endio specific version which won't touch any unsafe spinlock
+ * in endio context.
+ */
+static struct extent_buffer *find_extent_buffer_nospinlock(
+ struct btrfs_fs_info *fs_info, u64 start)
+{
+ struct extent_buffer *eb;
+
+ rcu_read_lock();
+ eb = radix_tree_lookup(&fs_info->buffer_radix,
+ start >> fs_info->sectorsize_bits);
+ if (eb && atomic_inc_not_zero(&eb->refs)) {
+ rcu_read_unlock();
+ return eb;
+ }
+ rcu_read_unlock();
+ return NULL;
+}
+/*
+ * The endio function for subpage extent buffer write.
+ *
+ * Unlike end_bio_extent_buffer_writepage(), we only call end_page_writeback()
+ * after all extent buffers in the page has finished their writeback.
+ */
+static void end_bio_subpage_eb_writepage(struct btrfs_fs_info *fs_info,
+ struct bio *bio)
+{
+ struct bio_vec *bvec;
+ struct bvec_iter_all iter_all;
+
+ ASSERT(!bio_flagged(bio, BIO_CLONED));
+ bio_for_each_segment_all(bvec, bio, iter_all) {
+ struct page *page = bvec->bv_page;
+ u64 bvec_start = page_offset(page) + bvec->bv_offset;
+ u64 bvec_end = bvec_start + bvec->bv_len - 1;
+ u64 cur_bytenr = bvec_start;
+
+ ASSERT(IS_ALIGNED(bvec->bv_len, fs_info->nodesize));
+
+ /* Iterate through all extent buffers in the range */
+ while (cur_bytenr <= bvec_end) {
+ struct extent_buffer *eb;
+ int done;
+
+ /*
+ * Here we can't use find_extent_buffer(), as it may
+ * try to lock eb->refs_lock, which is not safe in endio
+ * context.
+ */
+ eb = find_extent_buffer_nospinlock(fs_info, cur_bytenr);
+ ASSERT(eb);
+
+ cur_bytenr = eb->start + eb->len;
+
+ ASSERT(test_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags));
+ done = atomic_dec_and_test(&eb->io_pages);
+ ASSERT(done);
+
+ if (bio->bi_status ||
+ test_bit(EXTENT_BUFFER_WRITE_ERR, &eb->bflags)) {
+ ClearPageUptodate(page);
+ set_btree_ioerr(page, eb);
+ }
+
+ btrfs_subpage_clear_writeback(fs_info, page, eb->start,
+ eb->len);
+ end_extent_buffer_writeback(eb);
+ /*
+ * free_extent_buffer() will grab spinlock which is not
+ * safe in endio context. Thus here we manually dec
+ * the ref.
+ */
+ atomic_dec(&eb->refs);
+ }
+ }
+ bio_put(bio);
+}
+
static void end_bio_extent_buffer_writepage(struct bio *bio)
{
+ struct btrfs_fs_info *fs_info;
struct bio_vec *bvec;
struct extent_buffer *eb;
int done;
struct bvec_iter_all iter_all;
+ fs_info = btrfs_sb(bio_first_page_all(bio)->mapping->host->i_sb);
+ if (fs_info->sectorsize < PAGE_SIZE)
+ return end_bio_subpage_eb_writepage(fs_info, bio);
+
You replace the write_one_eb() call with one specifically for subpage, why not
just use your special endio from there without polluting the normal writepage
helper? Thanks,
Josef
