On Sun, May 09, 2010 at 11:56:19AM +0800, tom.leiming@xxxxxxxxx wrote:
> From: Ming Lei <tom.leiming@xxxxxxxxx>
>
> This patch introduces macro of trace_ret_hardirqs_on, which will
> call asm_trace_hardirqs_on if I flag in the stored CPSR is zero.
>
> The patch adds trace_ret_hardirqs_on before returning to user
> or exception mode once disable_irq was called explicitly, which does
> fix the inbalance of hardirqs trace and make lockdep happy. The patch
> does fix this kind of lockdep warning below:
I'm not convinced that this is required in all the places you're adding
it. Eg, in the return-to-user case, userspace _always_ has IRQs
enabled, and when we enter kernel space from the exception handler, we
always enable IRQs. Returning from any syscall with IRQs disabled is a
bug, and so that _should_ produce a warning.
In fact, returning to user mode with IRQs disabled in _any_ case is a
bug.
Please provide your reasoning for adding this to every path.
Finally, using asm_trace_hardirqs_on is extremely expensive, and in
many cases the register saving is completely wasteful. That's why
places were doing this:
#ifdef CONFIG_TRACE_IRQFLAGS
tst r4, #PSR_I_BIT
bleq trace_hardirqs_on
#endif
which is much more efficient.
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