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Commit 6d511a8b authored by Ira Weiny's avatar Ira Weiny Committed by Greg Kroah-Hartman
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btrfs: fix raid6 qstripe kmap 



commit d70cef0d46729808dc53f145372c02b145c92604 upstream.

When a qstripe is required an extra page is allocated and mapped.  There
were 3 problems:

1) There is no corresponding call of kunmap() for the qstripe page.
2) There is no reason to map the qstripe page more than once if the
   number of bits set in rbio->dbitmap is greater than one.
3) There is no reason to map the parity page and unmap it each time
   through the loop.

The page memory can continue to be reused with a single mapping on each
iteration by raid6_call.gen_syndrome() without remapping.  So map the
page for the duration of the loop.

Similarly, improve the algorithm by mapping the parity page just 1 time.

Fixes: 5a6ac9ea ("Btrfs, raid56: support parity scrub on raid56")
CC: stable@vger.kernel.org # 4.4.x: c17af96554a8: btrfs: raid56: simplify tracking of Q stripe presence
CC: stable@vger.kernel.org # 4.4.x
Signed-off-by: default avatarIra Weiny <ira.weiny@intel.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1c3c5136

fs/btrfs/raid56.c

+10 −11
Original line number Diff line number Diff line
@@ -2341,16 +2341,21 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio, 
	SetPageUptodate(p_page);



	if (has_qstripe) {

		/* RAID6, allocate and map temp space for the Q stripe */

		q_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);

		if (!q_page) {

			__free_page(p_page);

			goto cleanup;

		}

		SetPageUptodate(q_page);

		pointers[rbio->real_stripes - 1] = kmap(q_page);

	}



	atomic_set(&rbio->error, 0);



	/* Map the parity stripe just once */

	pointers[nr_data] = kmap(p_page);



	for_each_set_bit(pagenr, rbio->dbitmap, rbio->stripe_npages) {

		struct page *p;

		void *parity;
@@ -2360,16 +2365,8 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio, 
			pointers[stripe] = kmap(p);

		}



		/* then add the parity stripe */

		pointers[stripe++] = kmap(p_page);



		if (has_qstripe) {

			/*

			 * raid6, add the qstripe and call the

			 * library function to fill in our p/q

			 */

			pointers[stripe++] = kmap(q_page);



			/* RAID6, call the library function to fill in our P/Q */

			raid6_call.gen_syndrome(rbio->real_stripes, PAGE_SIZE,

						pointers);

		} else {
@@ -2390,12 +2387,14 @@ static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio, 


		for (stripe = 0; stripe < nr_data; stripe++)

			kunmap(page_in_rbio(rbio, stripe, pagenr, 0));

		kunmap(p_page);

	}



	kunmap(p_page);

	__free_page(p_page);

	if (q_page)

	if (q_page) {

		kunmap(q_page);

		__free_page(q_page);

	}



writeback:

	/*