linux-kernel - [PATCH AUTOSEL 5.4 059/134] iomap: fix return value of iomap_dio_bio

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Message-Id: <20191211151150.19073-59-sashal@kernel.org>
Date:   Wed, 11 Dec 2019 10:10:35 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Jan Stancek <jstancek@...hat.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 5.4 059/134] iomap: fix return value of iomap_dio_bio_actor on 32bit systems

From: Jan Stancek <jstancek@...hat.com>

[ Upstream commit e9f930ac88a8936ccc2d021110c98810cf5aa810 ]

Naresh reported LTP diotest4 failing for 32bit x86 and arm -next
kernels on ext4. Same problem exists in 5.4-rc7 on xfs.

The failure comes down to:
  openat(AT_FDCWD, "testdata-4.5918", O_RDWR|O_DIRECT) = 4
  mmap2(NULL, 4096, PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7f7b000
  read(4, 0xb7f7b000, 4096)              = 0 // expects -EFAULT

Problem is conversion at iomap_dio_bio_actor() return. Ternary
operator has a return type and an attempt is made to convert each
of operands to the type of the other. In this case "ret" (int)
is converted to type of "copied" (unsigned long). Both have size
of 4 bytes:
    size_t copied = 0;
    int ret = -14;
    long long actor_ret = copied ? copied : ret;

    On x86_64: actor_ret == -14;
    On x86   : actor_ret == 4294967282

Replace ternary operator with 2 return statements to avoid this
unwanted conversion.

Fixes: 4721a6010990 ("iomap: dio data corruption and spurious errors when pipes fill")
Reported-by: Naresh Kamboju <naresh.kamboju@...aro.org>
Signed-off-by: Jan Stancek <jstancek@...hat.com>
Reviewed-by: Christoph Hellwig <hch@....de>
Reviewed-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/iomap/direct-io.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 1fc28c2da2790..7c58f51d7da74 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -318,7 +318,9 @@ zero_tail:
 		if (pad)
 			iomap_dio_zero(dio, iomap, pos, fs_block_size - pad);
 	}
-	return copied ? copied : ret;
+	if (copied)
+		return copied;
+	return ret;
 }
 
 static loff_t
-- 
2.20.1