linux-kernel - Re: [RT] seqlocks: use of PICK_FUNCTION breaks kernel compile when CONFIG_GENERIC

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Date:	Tue, 16 Oct 2007 09:52:46 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Remy Bohmer <linux@...mer.net>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org
Subject: Re: [RT] seqlocks: use of PICK_FUNCTION breaks kernel compile when
	CONFIG_GENERIC_TIME is NOT set

On Tue, 2007-10-16 at 10:35 +0200, Remy Bohmer wrote:
> Hello Daniel and Ingo,
> 
> I use 2.6.23-rt1 and the patch of Daniel below which seems to be in
> there breaks the compilation of the RT-kernel when CONFIG_GENERIC_TIME
> is NOT set.
> 
> It breaks in the do_gettimeofday(struct timeval *tv) code in the
> architecture specific code
> where there is a call to: seq = read_seqbegin_irqsave(&xtime_lock, flags);
> The PICK_FUNCTION implementation does not return anything, so the
> compile breaks here.
> 
> I am figuring out how to solve this problem nicely, but I have not
> found a nice solution yet. Attached I have put my hack to make it
> compile on ARM again, but maybe one of you can do a better proposal to
> fix this.

Here's another fix for this. I compile tested for ARM (!GENERIC_TIME) ,
but I didn't boot test .. Could you boot test this patch?

---

Move the read_seqbegin() call up in the chain so the value 
can be returned

Signed-off-by: Daniel Walker <dwalker@...sta.com>

---
 include/linux/seqlock.h |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

Index: linux-2.6.23/include/linux/seqlock.h
===================================================================
--- linux-2.6.23.orig/include/linux/seqlock.h
+++ linux-2.6.23/include/linux/seqlock.h
@@ -285,21 +285,20 @@ unsigned long __read_seqbegin_irqsave_ra
 	unsigned long flags;
 
 	local_irq_save(flags);
-	__read_seqbegin_raw(sl);
 	return flags;
 }
 
 static __always_inline unsigned long __read_seqbegin_irqsave(seqlock_t *sl)
 {
-	__read_seqbegin(sl);
 	return 0;
 }
 
 #define read_seqbegin_irqsave(lock, flags)			\
-do {								\
+({								\
 	flags = PICK_SEQ_OP_RET(__read_seqbegin_irqsave_raw,	\
 		__read_seqbegin_irqsave, lock);			\
-} while (0)
+	read_seqbegin(lock);					\
+})
 
 static __always_inline int
 __read_seqretry_irqrestore(seqlock_t *sl, unsigned iv, unsigned long flags)


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