Hi Srikar, I still hope some day I'll find the time to read the whole series ;) Trying to continue from where I have stopped, and it seems that this patch has a couple more problems. On 06/07, Srikar Dronamraju wrote: > > A probe is specified by a file:offset. While registering, a breakpoint > is inserted for the first consumer, On subsequent probes, the consumer > gets appended to the existing consumers. While unregistering a > breakpoint is removed if the consumer happens to be the last consumer. > All other unregisterations, the consumer is deleted from the list of > consumers. > > Probe specifications are maintained in a rb tree. A probe specification > is converted into a uprobe before store in a rb tree. A uprobe can be > shared by many consumers. register/unregister logic looks racy... Supose that uprobe U has a single consumer C and register_uprobe() is called with the same inode/offset, while another thread does unregister(U,C). - register() calls alloc_uprobe(), finds the entry in rb tree, and increments U->ref. But this doesn't add the new consumer. - uregister() does del_consumer(), and removes the single consumer C. then it takes uprobes_mutex, sees uprobe->consumers == NULL and calls delete_uprobe()->rb_erase() - register() continues, takes uprobes_mutex, re-inserts the breakpoints, finds the new consumer and succeeds. However, this uprobe is not in rb-tree, it was deleted by unregister. OTOH. Suppose we add the new uprobe. register()->alloc_uprobe() sets new_uprobe->ref == 2. If something goes wrong after that, register() does delete_uprobe() + put_uprobe(), new_uprobe->ref becomes 1 and we leak this uprobe. Oleg. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>