Why we have shared Memory Corruption ?

Issue

• Application Framework uses a Shared Memory region to store global information for use by all application processes.

• The region is approximately 4 MB and split into two parts with an 8k header and the remainder used for locks. The shared memory is allocated using the using the shmget()/shmat01263279() system calls, all processes attach to this region in READ/WRITE mode.

• As a consistency check, when the process attaches to the existing shared memory, it checks the “revision” field, this is currently set to 1 (as it has always been), if this values is not 1, then the process will exit with the error indicating that the revision is wrong.

• The application has recently encountered cases when this shared memory appears to become corrupt, which prevents the application processes from staring up. This causes a major operational problem whereby the application needs to be taken down, the shared memory removed, reinstated and the application restarted.

• It has been noticed that the Virtual Address returned by mmap, and shmat are very similar