Messages in this thread | | | Date | Thu, 24 Aug 2006 21:38:28 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] Fix x86_64 _spin_lock_irqsave() |
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On 24 Aug 2006 08:45:11 +0200 Andi Kleen <ak@suse.de> wrote:
> Edward Falk <efalk@google.com> writes: > > > Add spin_lock_string_flags and _raw_spin_lock_flags() to > > asm-x86_64/spinlock.h so that _spin_lock_irqsave() has the same > > semantics on x86_64 as it does on i386 and does *not* have interrupts > > disabled while it is waiting for the lock. > > Did it fix anything for you? >
It's the rendezvous-via-IPI problem. Suppose we want to capture all CPUs in an IPI handler (TSC sync, for example).
- CPUa holds read_lock(&tasklist_lock) - CPUb is spinning in write_lock_irq(&taslist_lock) - CPUa enters its IPI handler and spins - CPUb never takes the IPI and we're dead.
Re-enabling interrupts while we spin will prevent that. But I suspect that if we ever want to implement IPI rendezvous (and cannot use the stop_machine_run() thing) then we might still have problems. A valid optimisation (which we use in some places) is:
local_irq_save(flags); <stuff> write_lock(lock);
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