lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 17 Apr 2008 17:45:53 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Alan Stern <stern@...land.harvard.edu> Cc: Kernel development list <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>, Paul E McKenney <paulmck@...ux.vnet.ibm.com> Subject: Re: Semphore -> mutex in the device tree On Thu, 2008-04-17 at 11:22 -0400, Alan Stern wrote: > Peter: > > The obstacle to converting the semaphore in struct device to a mutex > has been that its tree-oriented usage pattern isn't compatible with > lockdep. > > In order to get around this and at least begin the conversion process, > how about adding a provision for making some classes of mutex invisible > to lockdep? I know it doesn't solve the fundamental problem, but maybe > it's a step in the right direction. the device lock has two problems with lockdep: 1) on suspend it takes more than MAX_LOCK_DEPTH (48) locks 2) tree nesting Lets start with the easy one first; would a similar solution to the radix tree locking as found in -rt work? http://programming.kicks-ass.net/kernel-patches/concurrent-pagecache/23-rc1-rt/radix-concurrent-lockdep.patch That does mean you have to set an effective max depth to the tree, is that a practical issue? The harder part is 1), holding _that_ many locks. Would something obscene like this work for you: struct device_suspend { wait_queue_head_t wait_queue; struct srcu_struct srcu; int suspend; } dev_suspend_state; void device_lock(struct device *dev) { again: srcu_read_lock(&dev_suspend_state.srcu); if (unlikely(rcu_dereference(dev_suspend_state.suspend))) { srcu_read_unlock(&dev_suspend_state.srcu); wait_event(&dev_suspend_state.wait_queue, !dev_suspend_state.suspend); goto again; } mutex_lock(&dev->mutex); } void device_unlock(struct device *dev) { mutex_unlock(&dev->mutex); srcu_read_unlock(&dev_suspend_state.srcu); } void device_suspend(void) { rcu_assign_pointer(dev_suspend_state.suspend, 1); synchronize_srcu(&dev_suspend_state.srcu); } void device_resume(void) { rcu_assign_pointer(dev_suspend_state.suspend, 0); wake_up_all(&dev_suspend_state.wait_queue); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists