On Thu, May 01, 2014 at 05:02:42PM -0400, Tejun Heo wrote: > Hello, Jiri. > > On Thu, May 01, 2014 at 10:17:44PM +0200, Jiri Kosina wrote: > > I agree that this expectation might really somewhat implicit and is not > > probably properly documented anywhere. The basic observation is "whenever > > kthread_should_stop() is being called, all data structures are in a > > consistent state and don't need any further updates in order to achieve > > consistency, because we can exit the loop immediately here", as > > kthread_should_stop() is the very last thing every freezable kernel thread > > But kthread_should_stop() doesn't necessarily imply that "we can exit > the loop *immediately*" at all. It just indicates that it should > terminate in finite amount of time. I don't think it'd be too
Just a bit of addition. Please note that kthread_should_stop(), along with the freezer test, is actually trickier than it seems. It's very easy to write code which works most of the time but misses wake up from kill when the timing is just right (or wrong). It should be interlocked with set_current_state() and other related queueing data structure accesses. This was several years ago but when I audited most kthread users in kernel, especially in combination with the freezer test which also has similar requirement, surprising percentage of users (at least several tens of pct) were getting it slightly wrong, so kthread_should_stop() really isn't used as "we can exit *immediately*". It just isn't that simple. Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
