On Tue, Feb 21, 2012 at 01:16:32PM -0500, Alan Stern wrote: > This patch (as1521b) fixes the interaction between usb-storage's > scanning thread and the freezer. The current implementation has a > race: If the device is unplugged shortly after being plugged in and > just as a system sleep begins, the scanning thread may get frozen > before the khubd task. Khubd won't be able to freeze until the > disconnect processing is complete, and the disconnect processing can't > proceed until the scanning thread finishes, so the sleep transition > will fail. > > The implementation in the 3.2 kernel suffers from an additional > problem. There the scanning thread calls set_freezable_with_signal(), > and the signals sent by the freezer will mess up the thread's I/O > delays, which are all interruptible. > > The solution to both problems is the same: Replace the kernel thread > used for scanning with a delayed-work routine on the system freezable > work queue. Freezable work queues have the nice property that you can > cancel a work item even while the work queue is frozen, and no signals > are needed. > > The 3.2 version of this patch solves the problem in Bugzilla #42730. > > Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> > CC: Seth Forshee <seth.forshee@xxxxxxxxxxxxx> > CC: <stable@xxxxxxxxxxxxxxx> > > --- > > V.2: Fix the unbind/freeze race by using a delayed-work routine > instead of calling kthread_create(). This looks great. There doesn't appear to be any way for an untimely device removal to interfere with freezing. Unfortunately I'm unable to fully test it at the moment. I haven't been able to reproduce the issue with any kernel I've built over the past couple of days, even older kernel versions that I'm certain exhibited the issue previously, even though I can still see it with older builds of the same kernel. Presumably this is because a toolchain update has affected the timing. I'll work on getting a build I can test, but even without testing I have high confidence that this solution will work. Seth -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
