On Wed, 31 Mar 2010 14:12:54 -0700 "H. Peter Anvin" <hpa@xxxxxxxxx> wrote: > On 03/31/2010 01:52 PM, Andrew Morton wrote: > > On Wed, 31 Mar 2010 13:47:23 -0700 > > Yinghai Lu <yinghai@xxxxxxxxxx> wrote: > > > >> spin_unlock_irq from arm is different from other archs? > > > > No, spin_unlock_irq() unconditionally enables interrupts on all > > architectures. > > So I found checkin 60ba96e546da45d9e22bb04b84971a25684e4d46 in the > bk-historic git tree: > > [PATCH] rwsem: Make rwsems use interrupt disabling spinlocks > > The attached patch makes read/write semaphores use interrupt disabling > spinlocks in the slow path, thus rendering the up functions and trylock > functions available for use in interrupt context. This matches the > regular semaphore behaviour. > > I've assumed that the normal down functions must be called with > interrupts enabled (since they might schedule), and used the > irq-disabling spinlock variants that don't save the flags. > > Signed-Off-By: David Howells <dhowells@xxxxxxxxxx> > Tested-by: Badari Pulavarty <pbadari@xxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx> > > What we have here is a case of this assumption being violated, because > the lock is taken with interrupts disabled on a path where contention > cannot happen (because the code is single-threaded at this point), but > the lock is taken due to reuse of generic code. > > The obvious way to fix this would be to use > spin_lock_irqsave..spin_lock_irqrestore in __down_read as well as in the > other locations; I don't have a good feel for what the cost of doing so > would be, though. On x86 it's fairly expensive simply because the only > way to save the state is to push it on the stack, which the compiler > doesn't deal well with, but this code isn't used on x86. > Well, it's all a bit nasty. kmem_cache_create() does a lot of stuff, including calling into the page allocator with GFP_KERNEL - expecting kmem_cache_create() to preserve local_irq_disable() is a bit optimistic. radix_tree_init() calls hotcpu_notifier() which also does mutex_lock(&cpu_add_remove_lock); The easiest fix is to reposition the interrutps-are-now-enabled point in start_kernel(). But I have a feeling that some versions of early_irq_init() won't like that. -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html