linux-kernel - [PATCH] afs: Fix partial writeback of large files on fsync and close

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Message-Id: <20210604175504.4055-1-marc.c.dionne@gmail.com>
Date:   Fri,  4 Jun 2021 14:55:04 -0300
From:   Marc Dionne <marc.c.dionne@...il.com>
To:     Marc Dionne <marc.dionne@...istor.com>,
        David Howells <dhowells@...hat.com>
Cc:     linux-afs@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] afs: Fix partial writeback of large files on fsync and close

From: Marc Dionne <marc.dionne@...istor.com>

In commit e87b03f5830e ("afs: Prepare for use of THPs"), the return
value for afs_write_back_from_locked_page was changed from a number
of pages to a length in bytes.  The loop in afs_writepages_region uses
the return value to compute the index that will be used to find dirty
pages in the next iteration, but treats it as a number of pages and
wrongly multiplies it by PAGE_SIZE.  This gives a very large index value,
potentially skipping any dirty data that was not covered in the first
pass, which is limited to 256M.

This causes fsync(), and indirectly close(), to only do a partial
writeback of a large file's dirty data.  The rest is eventually written
back by background threads after dirty_expire_centisecs.

Fixes: e87b03f5830e ("afs: Prepare for use of THPs")
Signed-off-by: Marc Dionne <marc.dionne@...istor.com>
---
 fs/afs/write.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 3edb6204b937..a523bb86915d 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -730,7 +730,7 @@ static int afs_writepages_region(struct address_space *mapping,
 			return ret;
 		}

-		start += ret * PAGE_SIZE;
+		start += ret;

 		cond_resched();
 	} while (wbc->nr_to_write > 0);
-- 
2.31.1