btrfs: raid56: allocate memory separately for rbio pointers

Currently inside alloc_rbio(), we allocate a larger memory to contain
the following members:

- struct btrfs_raid_rbio itself
- stripe_pages array
- bio_sectors array
- stripe_sectors array
- finish_pointers array

Then update rbio pointers to point the extra space after the rbio
structure itself.

Thus it introduced a complex CONSUME_ALLOC() macro to help the thing.

This is too hacky, and is going to make later pointers expansion harder.

This patch will change it to use regular kcalloc() for each pointer
inside btrfs_raid_bio, making the later expansion much easier.

And introduce a helper free_raid_bio_pointers() to free up all the
pointer members in btrfs_raid_bio, which will be used in both
free_raid_bio() and error path of alloc_rbio().
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/raid56.c

@@ -76,6 +76,14 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
 					 int need_check);
 static void scrub_parity_work(struct work_struct *work);
 
+static void free_raid_bio_pointers(struct btrfs_raid_bio *rbio)
+{
+	kfree(rbio->stripe_pages);
+	kfree(rbio->bio_sectors);
+	kfree(rbio->stripe_sectors);
+	kfree(rbio->finish_pointers);
+}
+
 static void free_raid_bio(struct btrfs_raid_bio *rbio)
 {
 	int i;
@@ -95,6 +103,7 @@ static void free_raid_bio(struct btrfs_raid_bio *rbio)
 	}
 
 	btrfs_put_bioc(rbio->bioc);
+	free_raid_bio_pointers(rbio);
 	kfree(rbio);
 }
 
@@ -918,7 +927,6 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 		BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits;
 	const unsigned int num_sectors = stripe_nsectors * real_stripes;
 	struct btrfs_raid_bio *rbio;
-	void *p;
 
 	/* PAGE_SIZE must also be aligned to sectorsize for subpage support */
 	ASSERT(IS_ALIGNED(PAGE_SIZE, fs_info->sectorsize));
@@ -928,14 +936,23 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 	 */
 	ASSERT(stripe_nsectors <= BITS_PER_LONG);
 
-	rbio = kzalloc(sizeof(*rbio) +
-		       sizeof(*rbio->stripe_pages) * num_pages +
-		       sizeof(*rbio->bio_sectors) * num_sectors +
-		       sizeof(*rbio->stripe_sectors) * num_sectors +
-		       sizeof(*rbio->finish_pointers) * real_stripes,
-		       GFP_NOFS);
+	rbio = kzalloc(sizeof(*rbio), GFP_NOFS);
 	if (!rbio)
 		return ERR_PTR(-ENOMEM);
+	rbio->stripe_pages = kcalloc(num_pages, sizeof(struct page *),
+				     GFP_NOFS);
+	rbio->bio_sectors = kcalloc(num_sectors, sizeof(struct sector_ptr),
+				    GFP_NOFS);
+	rbio->stripe_sectors = kcalloc(num_sectors, sizeof(struct sector_ptr),
+				       GFP_NOFS);
+	rbio->finish_pointers = kcalloc(real_stripes, sizeof(void *), GFP_NOFS);
+
+	if (!rbio->stripe_pages || !rbio->bio_sectors || !rbio->stripe_sectors ||
+	    !rbio->finish_pointers) {
+		free_raid_bio_pointers(rbio);
+		kfree(rbio);
+		return ERR_PTR(-ENOMEM);
+	}
 
 	bio_list_init(&rbio->bio_list);
 	INIT_LIST_HEAD(&rbio->plug_list);
@@ -955,21 +972,6 @@ static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
 	atomic_set(&rbio->error, 0);
 	atomic_set(&rbio->stripes_pending, 0);
 
-	/*
-	 * The stripe_pages, bio_sectors, etc arrays point to the extra memory
-	 * we allocated past the end of the rbio.
-	 */
-	p = rbio + 1;
-#define CONSUME_ALLOC(ptr, count)	do {				\
-		ptr = p;						\
-		p = (unsigned char *)p + sizeof(*(ptr)) * (count);	\
-	} while (0)
-	CONSUME_ALLOC(rbio->stripe_pages, num_pages);
-	CONSUME_ALLOC(rbio->bio_sectors, num_sectors);
-	CONSUME_ALLOC(rbio->stripe_sectors, num_sectors);
-	CONSUME_ALLOC(rbio->finish_pointers, real_stripes);
-#undef  CONSUME_ALLOC
-
 	ASSERT(btrfs_nr_parity_stripes(bioc->map_type));
 	rbio->nr_data = real_stripes - btrfs_nr_parity_stripes(bioc->map_type);