Messages in this thread | | | Date | Thu, 18 Feb 2010 12:02:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [patch 4/5] xtime_lock: Convert to raw_seqlock |
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On Thu, 18 Feb 2010, Peter Zijlstra wrote:
> On Wed, 2010-02-17 at 18:47 +0000, Thomas Gleixner wrote: > > > > xtime_lock needs a raw_spinlock in preempt-rt. Convert it to > > raw_seqlock and fix up all users. > > > s/raw_spinlock/raw_seqlock/ ? > > Maybe add an explanation on _why_ -rt needs this for the uninformed > amongst us. > > -rt switches to sleeping spinlocks, but since the vdso is basically > userspace it cannot schedule, hence we need to keep using actual > spinlocks (this is also the reason the vdso things must not call into > lockdep)
No, the read_seq side is not taking the lock. It's just the write side which is taking the spinlock to serialize against other writers.
xtime_lock is write locked in the timer interrupt context and therefor cannot take a sleeping spinlock.
Thanks,
tglx
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