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);
+
ASSERT(!bio_flagged(bio, BIO_CLONED));
bio_for_each_segment_all(bvec, bio, iter_all) {
struct page *page = bvec->bv_page;
@@ -5465,36 +5549,29 @@ struct extent_buffer *find_extent_buffer(struct
btrfs_fs_info *fs_info,
{
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();
- /*
- * Lock our eb's refs_lock to avoid races with
- * free_extent_buffer. When we get our eb it might be flagged
- * with EXTENT_BUFFER_STALE and another task running
- * free_extent_buffer might have seen that flag set,
- * eb->refs == 2, that the buffer isn't under IO (dirty and
- * writeback flags not set) and it's still in the tree (flag
- * EXTENT_BUFFER_TREE_REF set), therefore being in the process
- * of decrementing the extent buffer's reference count twice.
- * So here we could race and increment the eb's reference count,
- * clear its stale flag, mark it as dirty and drop our reference
- * before the other task finishes executing free_extent_buffer,
- * which would later result in an attempt to free an extent
- * buffer that is dirty.
- */
- if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
- spin_lock(&eb->refs_lock);
- spin_unlock(&eb->refs_lock);
- }
- mark_extent_buffer_accessed(eb, NULL);
- return eb;
+ eb = find_extent_buffer_nospinlock(fs_info, start);
+ if (!eb)
+ return NULL;
+ /*
+ * Lock our eb's refs_lock to avoid races with free_extent_buffer().
+ * When we get our eb it might be flagged with EXTENT_BUFFER_STALE and
+ * another task running free_extent_buffer() might have seen that flag
+ * set, eb->refs == 2, that the buffer isn't under IO (dirty and
+ * writeback flags not set) and it's still in the tree (flag
+ * EXTENT_BUFFER_TREE_REF set), therefore being in the process
+ * of decrementing the extent buffer's reference count twice.
+ * So here we could race and increment the eb's reference count,
+ * clear its stale flag, mark it as dirty and drop our reference
+ * before the other task finishes executing free_extent_buffer,
+ * which would later result in an attempt to free an extent
+ * buffer that is dirty.
+ */
+ if (test_bit(EXTENT_BUFFER_STALE, &eb->bflags)) {
+ spin_lock(&eb->refs_lock);
+ spin_unlock(&eb->refs_lock);
}
- rcu_read_unlock();
-
- return NULL;
+ mark_extent_buffer_accessed(eb, NULL);
+ return eb;
}
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
--
2.31.1
