On 03/22/2011 03:37 PM, Steven Rostedt wrote: > On Tue, Mar 22, 2011 at 03:02:01PM -0700, David Collins wrote: >> Assume that A has already called regulator_enable for S1 some time in the >> past. >> >> Consumer A thread execution: >> regulator_disable(S1) >> mutex_lock(S1) >> _regulator_disable(S1) >> _notifier_call_chain(S1) >> mutex_lock(L2) >> >> Consumer B thread execution: >> regulator_enable(L2) >> mutex_lock(L2) >> _regulator_enable(L2) >> mutex_lock(S1) >> >> The locks for S1 and L2 are taken in opposite orders in the two threads; >> therefore, it is possible to achieve deadlock. I am not sure about the >> best way to resolve this situation. Is there a correctness requirement >> that regulator_enable holds the child regulator's lock when it attempts to >> enable the parent regulator? Likewise, is the lock around >> _notifier_call_chain required? > > I'm curious, if you had enabled lockdep, do you get a warning? If not, > why not? > > Thanks, > > -- Steve > > -- > To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html I have tried running with lockdep enabled. It does not produce a warning about possible deadlock from locks being taken in opposite orders in two threads. I assume that this is because it can only keep track of locks taken in the current stack backtrace. It does produce a warning for regulator_disable by itself though on a regulator with a non-empty supply_list: ============================================= [ INFO: possible recursive locking detected ] 2.6.38-rc7+ #231 --------------------------------------------- sh/25 is trying to acquire lock: (&rdev->mutex){+.+...}, at: [<c0137ae4>] _notifier_call_chain+0x28/0x6c but task is already holding lock: (&rdev->mutex){+.+...}, at: [<c0138410>] regulator_disable+0x24/0x74 The locks that it is noting are different; one is for the parent regulator and the other is for the child regulator. Any thoughts? Thanks, David -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
