From e55a0de185726ca43e8a31d363ad73c4f0a6770b Mon Sep 17 00:00:00 2001
From: Qu Wenruo <wqu@suse.com>
Date: Mon, 27 Sep 2021 15:22:05 +0800
Subject: [PATCH] btrfs: rework page locking in __extent_writepage()
Pages passed to __extent_writepage() are always locked, but they may be
locked by different functions.
There are two types of locked page for __extent_writepage():
- Page locked by plain lock_page()
It should not have any subpage::writers count.
Can be unlocked by unlock_page().
This is the most common locked page for __extent_writepage() called
inside extent_write_cache_pages() or extent_write_full_page().
Rarer cases include the @locked_page from extent_write_locked_range().
- Page locked by lock_delalloc_pages()
There is only one caller, all pages except @locked_page for
extent_write_locked_range().
In this case, we have to call subpage helper to handle the case.
So here we introduce a helper, btrfs_page_unlock_writer(), to allow
__extent_writepage() to unlock different locked pages.
And since for all other callers of __extent_writepage() their pages are
ensured to be locked by lock_page(), also add an extra check for
epd::extent_locked to unlock such pages directly.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/extent_io.c | 15 ++++++++++++++-
fs/btrfs/subpage.c | 43 +++++++++++++++++++++++++++++++++++++++++++
fs/btrfs/subpage.h | 2 ++
3 files changed, 59 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 655e78ae376e5..18ef234fe3dc9 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -4051,6 +4051,7 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
struct extent_page_data *epd)
{
struct inode *inode = page->mapping->host;
+ struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
const u64 page_start = page_offset(page);
const u64 page_end = page_start + PAGE_SIZE - 1;
int ret;
@@ -4138,7 +4139,19 @@ static int __extent_writepage(struct page *page, struct writeback_control *wbc,
*/
if (PageError(page))
end_extent_writepage(page, ret, page_start, page_end);
- unlock_page(page);
+ if (epd->extent_locked) {
+ /*
+ * If epd->extent_locked, it's from extent_write_locked_range(),
+ * the page can either be locked by lock_page() or
+ * process_one_page().
+ * Let btrfs_page_unlock_writer() handle both cases.
+ */
+ ASSERT(wbc);
+ btrfs_page_unlock_writer(fs_info, page, wbc->range_start,
+ wbc->range_end + 1 - wbc->range_start);
+ } else {
+ unlock_page(page);
+ }
ASSERT(ret <= 0);
return ret;
}
diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index ed9936cdd267c..265b6aa1c662d 100644
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -690,3 +690,46 @@ void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info,
ASSERT(PagePrivate(page) && page->private);
ASSERT(subpage_test_bitmap_all_zero(fs_info, subpage, dirty));
}
+
+/*
+ * Handle different locked pages with different page sizes:
+ *
+ * - Page locked by plain lock_page()
+ * It should not have any subpage::writers count.
+ * Can be unlocked by unlock_page().
+ * This is the most common locked page for __extent_writepage() called
+ * inside extent_write_cache_pages() or extent_write_full_page().
+ * Rarer cases include the @locked_page from extent_write_locked_range().
+ *
+ * - Page locked by lock_delalloc_pages()
+ * There is only one caller, all pages except @locked_page for
+ * extent_write_locked_range().
+ * In this case, we have to call subpage helper to handle the case.
+ */
+void btrfs_page_unlock_writer(struct btrfs_fs_info *fs_info, struct page *page,
+ u64 start, u32 len)
+{
+ struct btrfs_subpage *subpage;
+
+ ASSERT(PageLocked(page));
+ /* For regular page size case, we just unlock the page */
+ if (fs_info->sectorsize == PAGE_SIZE)
+ return unlock_page(page);
+
+ ASSERT(PagePrivate(page) && page->private);
+ subpage = (struct btrfs_subpage *)page->private;
+
+ /*
+ * For subpage case, there are two types of locked page. With or
+ * without writers number.
+ *
+ * Since we own the page lock, no one else could touch subpage::writers
+ * and we are safe to do several atomic operations without spinlock.
+ */
+ if (atomic_read(&subpage->writers))
+ /* No writers, locked by plain lock_page() */
+ return unlock_page(page);
+
+ /* Have writers, use proper subpage helper to end it */
+ btrfs_page_end_writer_lock(fs_info, page, start, len);
+}
diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index 46224f959c348..7accb5c40d33b 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h
@@ -150,5 +150,7 @@ bool btrfs_subpage_clear_and_test_dirty(const struct btrfs_fs_info *fs_info,
void btrfs_page_assert_not_dirty(const struct btrfs_fs_info *fs_info,
struct page *page);
+void btrfs_page_unlock_writer(struct btrfs_fs_info *fs_info, struct page *page,
+ u64 start, u32 len);
#endif