Hi, Continuing with my experiments with the DLM user API, I am trying to use blocking AST callbacks, and find that the rules for the lifetime and ownership of the dlm_lksb struct are a bit surprising. This led me to some investigations, and the question at the end of this email. It looks like the kernel remembers the pointer to the lksb struct used to issue the dlm_lock call, and libdlm happily overwrites this piece of memory whenever the kernel issues an event related to that lock, including just before firing a BAST callback. It is a bit frustrating because I got caught by surprise wondering why something was smashing my stack, ie. the place where I had once laid out my dlm_lksb, thinking that it was okay to release its memory after the completion AST callback has completed. For now I have (apparently) working test code that deals with this in the following way: for a given lock (identified by its lockid), I keep two dlm_lksb structs and a bit indicating which of the two is free to use for conversions. I update the bit every time the CAST (not BAST) callback completes, thus doing some kind of double buffering. So I assume that: - each lock acquisition or conversion call gives ownership of the lksb to the kernel and libdlm (because a BAST callback can fire at any time and will overwrite the struct), causing the kernel/libdlm to forget about the previously owned lksb (meaning the caller can/should then dispose of it) - AST and BAST callbacks run in order, such that after the CAST completes, and until a conversion occurs, a BAST firing will only overwrite the lksb given on the last lock or conversion Are my assumptions correct? Cheers, Jean-Marc -- saffroy@xxxxxxxxx -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
