On Sun, Jan 22, 2017 at 06:45:14PM +0100, Mike Galbraith wrote: > On Sun, 2017-01-22 at 09:46 +0100, Mike Galbraith wrote: > > Greetings btrfs/lockdep wizards, > > > > RT trees have trouble with the BTRFS lockdep positive avoidance lock > > class dance (see disk-io.c). Seems the trouble is due to RT not having > > a means of telling lockdep that its rwlocks are recursive for read by > > the lock owner only, combined with the BTRFS lock class dance assuming > > that read_lock() is annotated rwlock_acquire_read(), which RT cannot > > do, as that would be a big fat lie. > > > > Creating a rt_read_lock_shared() for btrfs_clear_lock_blocking_rw() did > > indeed make lockdep happy as a clam for test purposes. (hm, submitting > > that would be excellent way to replenish frozen shark supply:) > > > > Ideas? Not having looked at anything much, currently lockdep does not in fact model rwlock properly as is. Note that rwlock is _not_ in fact reader biased like it used to be, that is, read_lock() will block if there is a pending writer (just like rwsem), with the exception when read_lock() happend in_interrupt() (because tasklist_lock). -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
