On Monday January 14, viro@xxxxxxxxxxxxxxxxxx wrote: > On Mon, Jan 14, 2008 at 02:21:45PM +1100, Neil Brown wrote: > > > Maybe it isn't there any more.... > > > > Once upon a time, when I > > echo remove > /sys/block/mdX/md/dev-YYY/state > > Egads. And just what will protect you from parallel callers > of state_store()? buffer->mutex does *not* do that - it only > gives you exclusion on given struct file. Run the command > above from several shells and you've got independent open > from each redirect => different struct file *and* different > buffer for each => no exclusion whatsoever. well in -mm, rdev_attr_store gets a lock on rdev->mddev->reconfig_mutex. It doesn't test is rdev->mddev is NULL though, so if the write happens after unbind_rdev_from_array, we lose. A test for NULL would be easy enough. And I think that the mddev won't actually disappear until the rdevs are all gone (you subsequent comment about kobject_del ordering seems to confirm that) so a simple test for NULL should be sufficient. > > And _that_ is present right in the mainline tree - it's unrelated > to -mm kobject changes. > > BTW, yes, you do have a deadlock there - kobject_del() will try to evict > children, which will include waiting for currently running ->store() > to finish, which will include the caller since .../state *is* a child of > that sucker. > > The real problem is the lack of any kind of exclusion considerations in > md.c itself, AFAICS. Fun with ordering is secondary (BTW, yes, it is > a problem - will sysfs ->store() to attribute between export_rdev() and > kobject_del() work correctly?) Probably not. The possibility that rdev->mddev could be NULL would break a lot of these. Maybe I should delay setting rdev->mddev to NULL until after the kobject_del. Then audit them all. Thanks. I'll see what I can some up with. NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
