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Date: Thu, 16 Jan 2014 15:26:03 -0500 (EST) From: Alan Stern <stern@...land.harvard.edu> To: Peter Zijlstra <peterz@...radead.org> cc: Oleg Nesterov <oleg@...hat.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Steven Rostedt <rostedt@...dmis.org>, Paul McKenney <paulmck@...ux.vnet.ibm.com>, Linus Torvalds <torvalds@...ux-foundation.org> Subject: Re: check && lockdep_no_validate (Was: lockdep: Introduce wait-type checks) On Thu, 16 Jan 2014, Peter Zijlstra wrote: > On Thu, Jan 16, 2014 at 06:43:48PM +0100, Oleg Nesterov wrote: > > But with or without this change the following code > > > > static DEFINE_MUTEX(m1); > > static DEFINE_MUTEX(mx); > > > > lockdep_set_novalidate_class(&mx); > > > > // m1 -> mx > > mutex_lock(&m1); > > mutex_lock(&mx); > > mutex_unlock(&mx); > > mutex_unlock(&m1); > > > > // mx -> m1 ; should trigger the warning ??? > > mutex_lock(&mx); > > mutex_lock(&m1); > > mutex_unlock(&m1); > > mutex_unlock(&mx); > > > > doesn't trigger the warning too. This is correct because > > lockdep_set_novalidate_class() means, well, no-validate. > > The question is: do we really want to avoid all validations? > > Good question. > > > Why lockdep_set_novalidate_class() was added? Unlees I missed > > something the problem is that (say) __driver_attach() can take > > the "same" lock twice, drivers/base/ lacks annotations. > > Indeed, the driver model locking always slips my mind but yes its > creative. Alan Stern seems to have a good grasp on it though. Mostly my "grasp" is just a firm belief that trying to manage locking throughout the entire driver tree is hopeless. Individual sub-portions of it are usually well behaved, but the thing as a whole is a mess. > > Perhaps we should change the meaning of lockdep_set_novalidate_class? > > (perhaps with rename). What do you think about the patch below? > > > > With this patch __lockdep_no_validate__ means "automatically nested", > > Yes, I suppose that might work, it would allow some validation. I haven't seen the patch, but I'm not so sure it will work. Suppose we have two devices, D1 and D2, and some other mutex, M. Then the locking pattern: lock(D1); lock(M); unlock(M); unlock(D1); generally should not conflict with: lock(M); lock(D2); unlock(D2); unlock(M); even though D1's and D2's locks belong to the same class. For example, M might be a mutex embedded in the private data associated with D1, and D2 might be a child of D1. Alan Stern -- 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/
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