[PATCH 3.17-rc4 v5 2/6] arm: fiq: Replace default FIQ handler
From: Russell King - ARM Linux <hidden>
Date: 2014-09-12 17:03:17
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On Thu, Sep 11, 2014 at 12:31:14PM +0100, Daniel Thompson wrote:
quoted hunk ↗ jump to hunk
- .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? 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. 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. -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net.