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.