linux-kernel - [PATCH AUTOSEL 5.4 438/459] bcache: fix incorrect data type usage in btree_flush

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Date:   Fri, 14 Feb 2020 11:01:28 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Coly Li <colyli@...e.de>, Dan Carpenter <dan.carpenter@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, Sasha Levin <sashal@...nel.org>,
        linux-bcache@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 438/459] bcache: fix incorrect data type usage in btree_flush_write()

From: Coly Li <colyli@...e.de>

[ Upstream commit d1c3cc34f5a78b38d2b809b289d912c3560545df ]

Dan Carpenter points out that from commit 2aa8c529387c ("bcache: avoid
unnecessary btree nodes flushing in btree_flush_write()"), there is a
incorrect data type usage which leads to the following static checker
warning:
	drivers/md/bcache/journal.c:444 btree_flush_write()
	warn: 'ref_nr' unsigned <= 0

drivers/md/bcache/journal.c
   422  static void btree_flush_write(struct cache_set *c)
   423  {
   424          struct btree *b, *t, *btree_nodes[BTREE_FLUSH_NR];
   425          unsigned int i, nr, ref_nr;
                                    ^^^^^^

   426          atomic_t *fifo_front_p, *now_fifo_front_p;
   427          size_t mask;
   428
   429          if (c->journal.btree_flushing)
   430                  return;
   431
   432          spin_lock(&c->journal.flush_write_lock);
   433          if (c->journal.btree_flushing) {
   434                  spin_unlock(&c->journal.flush_write_lock);
   435                  return;
   436          }
   437          c->journal.btree_flushing = true;
   438          spin_unlock(&c->journal.flush_write_lock);
   439
   440          /* get the oldest journal entry and check its refcount */
   441          spin_lock(&c->journal.lock);
   442          fifo_front_p = &fifo_front(&c->journal.pin);
   443          ref_nr = atomic_read(fifo_front_p);
   444          if (ref_nr <= 0) {
                    ^^^^^^^^^^^
Unsigned can't be less than zero.

   445                  /*
   446                   * do nothing if no btree node references
   447                   * the oldest journal entry
   448                   */
   449                  spin_unlock(&c->journal.lock);
   450                  goto out;
   451          }
   452          spin_unlock(&c->journal.lock);

As the warning information indicates, local varaible ref_nr in unsigned
int type is wrong, which does not matche atomic_read() and the "<= 0"
checking.

This patch fixes the above error by defining local variable ref_nr as
int type.

Fixes: 2aa8c529387c ("bcache: avoid unnecessary btree nodes flushing in btree_flush_write()")
Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
Signed-off-by: Coly Li <colyli@...e.de>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/md/bcache/journal.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index 33ddc5269e8dc..6730820780b06 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -422,7 +422,8 @@ int bch_journal_replay(struct cache_set *s, struct list_head *list)
 static void btree_flush_write(struct cache_set *c)
 {
 	struct btree *b, *t, *btree_nodes[BTREE_FLUSH_NR];
-	unsigned int i, nr, ref_nr;
+	unsigned int i, nr;
+	int ref_nr;
 	atomic_t *fifo_front_p, *now_fifo_front_p;
 	size_t mask;
 
-- 
2.20.1