* Oleg Nesterov <oleg@xxxxxxxxxx> [2011-07-24 20:07:13]: > 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. Thanks for the review and I sincerely hope you find time and that too at the earliest. > > 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. > Agree, I will move the alloc_uprobe under the mutex_lock. On a side_note: As per the current discussions in this thread, I plan to use inode->i_mutex so that we could serialize register/unregister if they are for two different files. > > > 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. > Agree: yes I will add a put_uprobe() just after delete_uprobe() but just before the goto. sidenote: Even this code will change based on the discussions we had on this topic. But I will ensure to make the appropriate changes are taken care of. -- Thanks and Regards Srikar > 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>