btrfs: free the allocated memory if btrfs_alloc_page_array() fails

[BUG]
If btrfs_alloc_page_array() fail to allocate all pages but part of the
slots, then the partially allocated pages would be leaked in function
btrfs_submit_compressed_read().

[CAUSE]
As explicitly stated, if btrfs_alloc_page_array() returned -ENOMEM,
caller is responsible to free the partially allocated pages.

For the existing call sites, most of them are fine:

- btrfs_raid_bio::stripe_pages
  Handled by free_raid_bio().

- extent_buffer::pages[]
  Handled btrfs_release_extent_buffer_pages().

- scrub_stripe::pages[]
  Handled by release_scrub_stripe().

But there is one exception in btrfs_submit_compressed_read(), if
btrfs_alloc_page_array() failed, we didn't cleanup the array and freed
the array pointer directly.

Initially there is still the error handling in commit dd137dd
("btrfs: factor out allocating an array of pages"), but later in commit
544fe4a ("btrfs: embed a btrfs_bio into struct compressed_bio"),
the error handling is removed, leading to the possible memory leak.

[FIX]
This patch would add back the error handling first, then to prevent such
situation from happening again, also
Make btrfs_alloc_page_array() to free the allocated pages as a extra
safety net, then we don't need to add the error handling to
btrfs_submit_compressed_read().

Fixes: 544fe4a ("btrfs: embed a btrfs_bio into struct compressed_bio")
CC: [email protected] # 6.4+
Reviewed-by: Filipe Manana <[email protected]>
Signed-off-by: Qu Wenruo <[email protected]>
Reviewed-by: David Sterba <[email protected]>
Signed-off-by: David Sterba <[email protected]>

Author: adam900710

fs/btrfs/extent_io.c

@@ -674,8 +674,8 @@ static void end_bio_extent_readpage(struct btrfs_bio *bbio)
  * 		the array will be skipped
  *
  * Return: 0        if all pages were able to be allocated;
- *         -ENOMEM  otherwise, and the caller is responsible for freeing all
- *                  non-null page pointers in the array.
+ *         -ENOMEM  otherwise, the partially allocated pages would be freed and
+ *                  the array slots zeroed
  */
 int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
 {
@@ -694,8 +694,13 @@ int btrfs_alloc_page_array(unsigned int nr_pages, struct page **page_array)
 		 * though alloc_pages_bulk_array() falls back to alloc_page()
 		 * if  it could not bulk-allocate. So we must be out of memory.
 		 */
-		if (allocated == last)
+		if (allocated == last) {
+			for (int i = 0; i < allocated; i++) {
+				__free_page(page_array[i]);
+				page_array[i] = NULL;
+			}
 			return -ENOMEM;
+		}
 
 		memalloc_retry_wait(GFP_NOFS);
 	}