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Date: Sat, 13 Sep 2014 13:01:20 +0100 From: Daniel Thompson <daniel.thompson@...aro.org> To: Russell King - ARM Linux <linux@....linux.org.uk> CC: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, patches@...aro.org, linaro-kernel@...ts.linaro.org, John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Sumit Semwal <sumit.semwal@...aro.org>, Catalin Marinas <catalin.marinas@....com> Subject: Re: [PATCH 3.17-rc4 v5 2/6] arm: fiq: Replace default FIQ handler On 12/09/14 18:03, Russell King - ARM Linux wrote: > On Thu, Sep 11, 2014 at 12:31:14PM +0100, Daniel Thompson wrote: >> - .macro svc_entry, stack_hole=0 >> + .macro svc_entry, stack_hole=0, call_trace=1 >> UNWIND(.fnstart ) >> UNWIND(.save {r0 - pc} ) >> sub sp, sp, #(S_FRAME_SIZE + \stack_hole - 4) >> @@ -183,7 +183,9 @@ ENDPROC(__und_invalid) >> stmia r7, {r2 - r6} >> >> #ifdef CONFIG_TRACE_IRQFLAGS >> + .if \call_trace >> bl trace_hardirqs_off >> + .endif >> #endif > > Good, you picked this up from my patch. But what about the call into > lockdep from usr_entry? That was writen from your review comment rather than taken from your patch. > Yes, it should be safe if we're entering from user mode, because by > definition, the kernel can't be holding any locks at that point. > However, I'd much prefer to keep to a set of simple rules here: avoid > lockdep in FIQ code altogether. Ok. You're right that I followed the "can't be holding any locks" logic when I didn't update usr_entry in reaction to the original review comment. I'm also happy with the "avoid lockdep in FIQ code altogether" approach. I'll do this. > That's much easier to understand than "we can call into lockdep provided > we've been entered from user mode". > > The other thing you miss is that /potentially/ call into the scheduler > as well from a FIQ. Do we /really/ want to do that kind of work here? > > Not happy. Sorry. I will fix these. Daniel. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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