On Sun, Mar 30, 2008 at 03:56:18PM -0400, Joey Hess wrote: > Package: menu > Version: 2.1.39 > Severity: normal > > I think I've found a locking bug race in update-menus. This was found by > inspection, I don't know how realistically it happens in the wild. > > Many apt-driven upgrades invoke dpkg multiple times. update-menus can > be run inside each dpkg invocation. It forks to the background, and > begins checking dpkg's lock file to see when dpkg exits. The check used > is to call fcntl(F_GETLCK) to see if the lock is available to be taken > (but not actually take it). If the lock is not available, it sleeps for > 2 seconds. Now consider the following sequence of events: > > * apt run > * dpkg run #1 > * update-menus run, forks to background > * update-menus checks dpkg lock -- still locked > * update-menus sleeps for 2 seconds > * 1.9999 seconds later, dpkg run #1 finishes > * update-menus runs fcntl(F_GETLCK) at just the right time, > sees that dpkg is not running > * update-menus begins reading menu files > * dpkg run #2 starts > * update-menus finishes reading the files, begins generating menus > * dpkg adds a new menu file > * update-menus is run a second time > * since the first update-menus is still running, the second one > exists w/o doing anything > * the first update-menus finishes generating menus. But these > menus do not include the item from the new menu file. > > I suspect that we don't see this in the wild often because of the 2 second > sleep. That narrows the window of the race considerably, without closing it. > > Plus, there are really two races that have to happen for the problem to > occur. If the first update-menus exits before the second one runs.
This is a known issue. A simpler way to trigger it is to run dpkg manually after apt. But since it does not result in two update-menus running at the same time, nor in a garbled menu, but only on a slighlty outdated menu, it is sufficiently hard to trigger so that is not considered a serious issue. Cheers, -- Bill. <[EMAIL PROTECTED]> Imagine a large red swirl here. -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
