On Wed, Dec 21, 2005 at 10:35:19AM -0800, Stephen Hemminger wrote: > Right now there is a hole in the module ref counting system because > there is no proper ref counting for sysctl tables used by modules. > This means that if an application is holding /proc/sys/foo open and > module that created it is unloaded, then the application touches the > file the kernel will oops. > > This patch fixes that by maintaining source compatibility via macro. > I am sure someone already thought of this, it just doesn't appear to > have made it in yet.
NAK. a) holding the file open will *NOT* pin any module structures down. IO in progress will, but it unregistering sysctl table will block until it's over. The same goes for sysctl(2) in progress. See use_table() and friends in kernel/sysctl.c b) you are not protecting any code in module; what needs protection (and gets it) is a pile of data structures. With lifetimes that don't have to be related to module lifetimes. IOW, use of reference to module is 100% wrong here - it wouldn't fix anything. As a general rule, when you pin something down, think what you are trying to protect; if it's not just a bunch of function references - module is the wrong thing to hold. In particular, sysctl tables are dynamically created and removed in a kernel that is not modular at all. Which kills any hope to get a solution based on preventing rmmod. Solution is fairly simple: * put use counter into sysctl table head (i.e. object allocated by kernel/sysctl.c) * bump use counter when examining table in sysctl(2) and around the actual IO in procfs access; put reference to table into proc_dir_entry to be able to do the latter. Decrement when done with the table; if it had hit zero _and_ there's unregistration waiting for completion - kick it. * have unregistration kill all reference to table head and if use counter is positive - wait for completion. Once we get it, we know that we can safely proceed. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html