Skip to contentSkip to conversation

FAILED: patch "[PATCH] btrfs: fix raid6 qstripe kmap" failed to apply to 4.4-stable tree

PATCH [email protected] 1 participant 1 message Mar 7, 2021

Subsystems (2)
Stable branch Btrfs file system
lore
Share & tools
lore

[email protected]

author maintainer
#0 lore raw

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d70cef0d46729808dc53f145372c02b145c92604 Mon Sep 17 00:00:00 2001
From: Ira Weiny <[email protected]>
Date: Wed, 27 Jan 2021 22:15:03 -0800
Subject: [PATCH] btrfs: fix raid6 qstripe kmap

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 5a6ac9eacb49 ("Btrfs, raid56: support parity scrub on raid56")
CC [email protected] # 4.4.x: c17af96554a8: btrfs: raid56: simplify tracking of Q stripe presence
CC [email protected] # 4.4.x
Signed-off-by Ira Weiny <[email protected]>
Reviewed-by David Sterba <[email protected]>
Signed-off-by David Sterba <[email protected]>
fs/btrfs/raid56.c +10 -11
index 5394641541f7..abf17fae0912 100644
@@ -2362,16 +2362,21 @@ 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;

@@ -2381,16 +2386,8 @@ 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 {

@@ -2411,12 +2408,14 @@ 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:
 	/*