From d130b5fdd42254d92948d06347940276140c927e Mon Sep 17 00:00:00 2001

From: David Howells <dhowells@redhat.com>

Date: Wed, 1 Sep 2021 09:15:21 +0100

Subject: [PATCH] afs: Fix page leak

Git-commit: 581b2027af0018944ba301d68e7af45c6d1128b5

Patch-mainline: v5.15-rc3

References: stable-5.14.9

[ Upstream commit 581b2027af0018944ba301d68e7af45c6d1128b5 ]

There's a loop in afs_extend_writeback() that adds extra pages to a write

we want to make to improve the efficiency of the writeback by making it

larger.  This loop stops, however, if we hit a page we can't write back

from immediately, but it doesn't get rid of the page ref we speculatively

acquired.

This was caused by the removal of the cleanup loop when the code switched

from using find_get_pages_contig() to xarray scanning as the latter only

gets a single page at a time, not a batch.

Fix this by putting the page on a ref on an early break from the loop.

Unfortunately, we can't just add that page to the pagevec we're employing

as we'll go through that and add those pages to the RPC call.

This was found by the generic/074 test.  It leaks ~4GiB of RAM each time it

is run - which can be observed with "top".

Fixes: e87b03f5830e ("afs: Prepare for use of THPs")

Reported-by: Marc Dionne <marc.dionne@auristor.com>

Signed-off-by: David Howells <dhowells@redhat.com>

Reviewed-and-tested-by: Marc Dionne <marc.dionne@auristor.com>

Cc: linux-afs@lists.infradead.org

Link: https://lore.kernel.org/r/163111666635.283156.177701903478910460.stgit@warthog.procyon.org.uk/

Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 fs/afs/write.c | 10 ++++++++--

 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c

index c0534697268e..66b235266893 100644

--- a/fs/afs/write.c

+++ b/fs/afs/write.c

@@ -471,13 +471,18 @@ static void afs_extend_writeback(struct address_space *mapping,

 			}

 			/* Has the page moved or been split? */

-			if (unlikely(page != xas_reload(&xas)))

+			if (unlikely(page != xas_reload(&xas))) {

+				put_page(page);

 				break;

+			}

-			if (!trylock_page(page))

+			if (!trylock_page(page)) {

+				put_page(page);

 				break;

+			}

 			if (!PageDirty(page) || PageWriteback(page)) {

 				unlock_page(page);

+				put_page(page);

 				break;

 			}

@@ -487,6 +492,7 @@ static void afs_extend_writeback(struct address_space *mapping,

 			t = afs_page_dirty_to(page, priv);

 			if (f != 0 && !new_content) {

 				unlock_page(page);

+				put_page(page);

 				break;

 			}

-- 

2.26.2