Re: LTP: diotest4.c:476: read to read-only space. returns 0: Success

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> LTP test case dio04 test failed on 32bit kernel running linux next
> 20191107 kernel.
> Linux version 5.4.0-rc6-next-20191107.
> 
> diotest4    1  TPASS  :  Negative Offset
> diotest4    2  TPASS  :  removed
> diotest4    3  TPASS  :  Odd count of read and write
> diotest4    4  TPASS  :  Read beyond the file size
> diotest4    5  TPASS  :  Invalid file descriptor
> diotest4    6  TPASS  :  Out of range file descriptor
> diotest4    7  TPASS  :  Closed file descriptor
> diotest4    8  TPASS  :  removed
> diotest4    9  TCONF  :  diotest4.c:345: Direct I/O on /dev/null is
> not supported
> diotest4   10  TPASS  :  read, write to a mmaped file
> diotest4   11  TPASS  :  read, write to an unmapped file
> diotest4   12  TPASS  :  read from file not open for reading
> diotest4   13  TPASS  :  write to file not open for writing
> diotest4   14  TPASS  :  read, write with non-aligned buffer
> diotest4   15  TFAIL  :  diotest4.c:476: read to read-only space.
> returns 0: Success
> diotest4   16  TFAIL  :  diotest4.c:180: read, write buffer in read-only
> space
> diotest4   17  TFAIL  :  diotest4.c:114: read allows  nonexistant
> space. returns 0: Success
> diotest4   18  TFAIL  :  diotest4.c:129: write allows  nonexistant
> space.returns -1: Invalid argument
> diotest4   19  TFAIL  :  diotest4.c:180: read, write in non-existant space
> diotest4   20  TPASS  :  read, write for file with O_SYNC
> diotest4    0  TINFO  :  2/15 test blocks failed

Smaller reproducer for 32-bit system and ext4 is:
  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 appears to be conversion in ternary operator at
iomap_dio_bio_actor() return. Test passes for me with
following tweak:

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 2f88d64c2a4d..8615b1f78389 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -318,7 +318,7 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
                if (pad)
                        iomap_dio_zero(dio, iomap, pos, fs_block_size - pad);
        }
-       return copied ? copied : ret;
+       return copied ? (loff_t) copied : ret;
 }

 static loff_t