SIGBUS while doing memcpy from mmap ed buffer whic

Question

I am mmapping a block as:

mapAddr = mmap((void*) 0, curMapSize, PROT_NONE, MAP_LOCKED|MAP_SHARED, fd, curMapOffset);

if this does not fail (mapAddr != MAP_FAILED) I query mincore as:

err = mincore((char*) mapAddr, pageSize, &mincoreRet);

to find out whether it is in RAM. In case it is in RAM (err == 0 && mincoreRet & 0x01) I mmap it again for reading as:

copyAddr = mmap((void*) 0, curMapSize, PROT_READ, MAP_LOCKED|MAP_SHARED, fd, curMapOffset);

and then I try to copy it out to my buffer as:

memcpy(data, copyAddr, pageSize);

everything works fine except in the last memcpy once in a while I get SIGBUS. When I check /proc/ /smaps at the time of the failure I notice that it has Rss as well as Locked fields as 0 as listed below:

7f4a4c118000-7f4a4c119000 r--s 00326000 00:17 6                          <file name>

Size:                  4 kB

Rss:                   0 kB

Pss:                   0 kB

Shared_Clean:          0 kB

Shared_Dirty:          0 kB

Private_Clean:         0 kB

Private_Dirty:         0 kB

Referenced:            0 kB

Anonymous:             0 kB

AnonHugePages:         0 kB

Swap:                  0 kB

KernelPageSize:        4 kB

MMUPageSize:           4 kB

Locked:                0 kB

Any thoughts? This is happening on ubuntu 12.0.4 with kernel version 3.5.0-36.