Messages in this thread | | | Date | Wed, 29 Apr 2009 07:55:12 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH 1/5] tracing: convert ftrace_dump spinlocks to raw |
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* Andrew Morton <akpm@linux-foundation.org> wrote:
> On Wed, 29 Apr 2009 00:48:15 -0400 Steven Rostedt <rostedt@goodmis.org> wrote: > > > + local_irq_save(flags); > > + __raw_spin_lock(&ftrace_dump_lock); > > I'm counting twentyish instances of this. [...]
there's 9 in the tracing code, two more in the rest of the kernel.
> [...] Maybe it's time to give up and implement > raw_spin_lock_irqsave().
There's a difference between:
local_irq_save(flags); __raw_spin_lock(&ftrace_dump_lock);
and:
raw_local_irq_save(flags); __raw_spin_lock(&ftrace_dump_lock);
raw_spin_lock_irqsave() would map to the latter logic-wise - but in the tracing code we want the former.
But the main reason is that using raw locks has its costs - it skips lockdep coverage, is preempt unsafe, etc. The APIs are not complete and intentionally so: they are minimal building blocks for the real APIs. Instrumentation goes deep in the guts of the kernel so using very low level primitives is justified there - but we dont want to make it _too_ easy to use a raw-anything locking facility.
Ingo
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