On Mon, Nov 11, 2019 at 11:28:10AM +0100, Jan Stancek wrote:
> 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@xxxxxxxxxx>
> Signed-off-by: Jan Stancek <jstancek@xxxxxxxxxx>
Thansk for the full explanation & patch, will test...
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
> 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 1fc28c2da279..7c58f51d7da7 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -318,7 +318,9 @@ static void iomap_dio_bio_end_io(struct bio *bio)
> 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
> --
> 1.8.3.1
>
