btrfs: extent_io: add proper error handling to lock_extent_buffer_for_io()

This function needs some extra checks on locked pages and eb.  For error
handling we need to unlock locked pages and the eb.

There is a rare >0 return value branch, where all pages get locked
while write bio is not flushed.

Thankfully it's handled by the only caller, btree_write_cache_pages(),
as later write_one_eb() call will trigger submit_one_bio().  So there
shouldn't be any problem.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index b43a0a0..38dcac0 100644 (file)
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3492,19 +3492,27 @@ void wait_on_extent_buffer_writeback(struct extent_buffer *eb)
                       TASK_UNINTERRUPTIBLE);
 }
 
+/*
+ * Lock eb pages and flush the bio if we can't the locks
+ *
+ * Return  0 if nothing went wrong
+ * Return >0 is same as 0, except bio is not submitted
+ * Return <0 if something went wrong, no page is locked
+ */
 static noinline_for_stack int
 lock_extent_buffer_for_io(struct extent_buffer *eb,
                          struct btrfs_fs_info *fs_info,
                          struct extent_page_data *epd)
 {
-       int i, num_pages;
+       int i, num_pages, failed_page_nr;
        int flush = 0;
        int ret = 0;
 
        if (!btrfs_try_tree_write_lock(eb)) {
-               flush = 1;
                ret = flush_write_bio(epd);
-               BUG_ON(ret < 0);
+               if (ret < 0)
+                       return ret;
+               flush = 1;
                btrfs_tree_lock(eb);
        }
 
@@ -3514,7 +3522,8 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
                        return 0;
                if (!flush) {
                        ret = flush_write_bio(epd);
-                       BUG_ON(ret < 0);
+                       if (ret < 0)
+                               return ret;
                        flush = 1;
                }
                while (1) {
@@ -3556,7 +3565,10 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
                if (!trylock_page(p)) {
                        if (!flush) {
                                ret = flush_write_bio(epd);
-                               BUG_ON(ret < 0);
+                               if (ret < 0) {
+                                       failed_page_nr = i;
+                                       goto err_unlock;
+                               }
                                flush = 1;
                        }
                        lock_page(p);
@@ -3564,6 +3576,11 @@ lock_extent_buffer_for_io(struct extent_buffer *eb,
        }
 
        return ret;
+err_unlock:
+       /* Unlock already locked pages */
+       for (i = 0; i < failed_page_nr; i++)
+               unlock_page(eb->pages[i]);
+       return ret;
 }
 
 static void end_extent_buffer_writeback(struct extent_buffer *eb)