Messages in this thread | | | Date | Fri, 24 Feb 2006 10:03:42 -0500 (EST) | From | Alan Stern <> | Subject | Re: [PATCH] Avoid calling down_read and down_write during startup |
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On Fri, 24 Feb 2006, Benjamin LaHaise wrote:
> On Thu, Feb 23, 2006 at 04:16:31PM -0800, Andrew Morton wrote: > > down_write() unconditionally (and reasonably) does local_irq_enable() in > > the uncontended case. And enabling local interrupts early in boot can > > cause crashes. > > Why not do a down_write_trylock() instead first? Then the code doesn't > have the dependancy on system_state, which seems horribly fragile.
I suggested this to Andrew. His reply was as follows:
> > which means we can't avoid calling down_write. The > > only solution I can think of is to use down_write_trylock in the > > blocking_notifier_chain_register and unregister routines, even though > > doing that is a crock. > > > > Or else change __down_read and __down_write to use spin_lock_irqsave > > instead of spin_lock_irq. What do you think would be best? > > Nothing's pretty. Perhaps look at system_state and not do any locking at all > in early boot?
I admit that the whole things is fragile. IMO the safest approach would be for __down_read and __down_write not to assume that interrupts are currently enabled. But that would introduce more overhead as well; at least this way the overhead is confined to the notifier chain registration routines.
Alan Stern
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