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Subject: [PATCH v2 2/4] afs: check function return
From:   David Howells <dhowells@redhat.com>
To:     linux-afs@lists.infradead.org
Cc:     Tom Rix <trix@redhat.com>, dhowells@redhat.com,
        Marc Dionne <marc.dionne@auristor.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Mon, 12 Jul 2021 17:27:56 +0100
Message-ID: <162610727640.3408253.8687445613469681311.stgit@warthog.procyon.org.uk>
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From: Tom Rix <trix@redhat.com>

Static analysis reports this problem

write.c:773:29: warning: Assigned value is garbage or undefined
  mapping->writeback_index = next;
                           ^ ~~~~
The call to afs_writepages_region() can return without setting
next.  So check the function return before using next.

Changes:
 ver #2:
   - Need to fix the range_cyclic case also[1].

Fixes: e87b03f5830e ("afs: Prepare for use of THPs")
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20210430155031.3287870-1-trix@redhat.com
Link: https://lore.kernel.org/r/162609464716.3133237.10354897554363093252.stgit@warthog.procyon.org.uk/ # v1
Link: https://lore.kernel.org/r/CAB9dFdvHsLsw7CMnB+4cgciWDSqVjuij4mH3TaXnHQB8sz5rHw@mail.gmail.com/ [1]
---

 fs/afs/write.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 3104b62c2082..1ed62e0ccfe5 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -771,13 +771,19 @@ int afs_writepages(struct address_space *mapping,
 	if (wbc->range_cyclic) {
 		start = mapping->writeback_index * PAGE_SIZE;
 		ret = afs_writepages_region(mapping, wbc, start, LLONG_MAX, &next);
-		if (start > 0 && wbc->nr_to_write > 0 && ret == 0)
-			ret = afs_writepages_region(mapping, wbc, 0, start,
-						    &next);
-		mapping->writeback_index = next / PAGE_SIZE;
+		if (ret == 0) {
+			mapping->writeback_index = next / PAGE_SIZE;
+			if (start > 0 && wbc->nr_to_write > 0) {
+				ret = afs_writepages_region(mapping, wbc, 0,
+							    start, &next);
+				if (ret == 0)
+					mapping->writeback_index =
+						next / PAGE_SIZE;
+			}
+		}
 	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
 		ret = afs_writepages_region(mapping, wbc, 0, LLONG_MAX, &next);
-		if (wbc->nr_to_write > 0)
+		if (wbc->nr_to_write > 0 && ret == 0)
 			mapping->writeback_index = next;
 	} else {
 		ret = afs_writepages_region(mapping, wbc,