Fix io_u->buf calculation overflow

Fix io_u->buf calculation overflow

Jagadish reports:

----

following are the details of the bug in fio.

This bug in fio can show up as corruption of data when performing verify.

Description:
----------------

if  the product of block size and queudepth is greater than 4GB, io_u
buffer will not
be assigned properly due to overflow.

fio --bsrange=256k-4m --ioengine=libaio --iodepth=2064 --direct=1
--name=job3 --offset=2GB --size=14GB --rw=write
--verify_pattern=0xdeadbeef --filename=/dev/sdb

can show false corruption.

Version:
-----------
1.58

Explanation:
-----------------

in a loop fio tries to assign the data buffer to each i/o request.

static int init_io_u(struct thread_data *td)
{
        struct io_u *io_u;
        unsigned int max_bs;
        int cl_align, i, max_units;
        char *p;
...
         p = td->orig_buffer;
...
         for (i = 0; i < max_units; i++) {
...
                    io_u->buf = p + max_bs * i;
         }
}

at max_bs=4M i=1024, the integer overflows and the addresses are being
used again.
i,e i/o request 1024 will have the same data buffer as that of i/o request 0.

This is seen from fio debug log.

mem 11164 io_u alloc 0x219f530, index 0
mem 11164 io_u 0x219f530, mem 0x7f09bb62d000
mem 11164 io_u alloc 0x219f820, index 1
mem 11164 io_u 0x219f820, mem 0x7f09bba2d000

mem 11164 io_u alloc 0x225b530, index 1024
mem 11164 io_u 0x225b530, mem 0x7f09bb62d000
mem 11164 io_u alloc 0x225b820, index 1025
mem 11164 io_u 0x225b820, mem 0x7f09bba2d000

the fix is as follows:

                        io_u->buf = p + (unsigned long long)max_bs * i;

----

Fix this by continually incrementing 'p' instead, avoiding
the overflow as well.

Reported-by: Jagadish Kumar <jagadish.mukku@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>