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Re: [PATCH] atomic functions broken

To: Thomas Koeller <thomas.koeller@baslerweb.com>
Subject: Re: [PATCH] atomic functions broken
From: Ralf Baechle <ralf@linux-mips.org>
Date: Thu, 23 Feb 2006 14:09:47 +0000
Cc: linux-mips@linux-mips.org
In-reply-to: <200602222125.39999.thomas.koeller@baslerweb.com>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <200602222125.39999.thomas.koeller@baslerweb.com>
Sender: linux-mips-bounce@linux-mips.org
User-agent: Mutt/1.4.2.1i
On Wed, Feb 22, 2006 at 09:25:39PM +0100, Thomas Koeller wrote:

> The ll/sc versions of atomic_sub_if_positive(), and the corresponding 64-bit 
> functions,
> are broken. The value returned by those functions is always one, no matter 
> what.

Good catch - and I wonder how you found this bug since it didn't seem to
cause any obvious damage.  I just went for a different fix though - I was
able to get away without an extra register and squeeze the needed extra
instruction into a delay slot, so no code size penalty either.

  Ralf

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

--- a/include/asm-mips/atomic.h
+++ b/include/asm-mips/atomic.h
@@ -250,7 +250,10 @@ static __inline__ int atomic_sub_if_posi
                "       subu    %0, %1, %3                              \n"
                "       bltz    %0, 1f                                  \n"
                "       sc      %0, %2                                  \n"
+               "       .set    noreorder                               \n"
                "       beqzl   %0, 1b                                  \n"
+               "        subu   %0, %1, %3                              \n"
+               "       .set    reorder                                 \n"
                "       sync                                            \n"
                "1:                                                     \n"
                "       .set    mips0                                   \n"
@@ -266,7 +269,10 @@ static __inline__ int atomic_sub_if_posi
                "       subu    %0, %1, %3                              \n"
                "       bltz    %0, 1f                                  \n"
                "       sc      %0, %2                                  \n"
+               "       .set    noreorder                               \n"
                "       beqz    %0, 1b                                  \n"
+               "        subu   %0, %1, %3                              \n"
+               "       .set    reorder                                 \n"
                "       sync                                            \n"
                "1:                                                     \n"
                "       .set    mips0                                   \n"
@@ -598,7 +604,10 @@ static __inline__ long atomic64_sub_if_p
                "       dsubu   %0, %1, %3                              \n"
                "       bltz    %0, 1f                                  \n"
                "       scd     %0, %2                                  \n"
+               "       .set    noreorder                               \n"
                "       beqzl   %0, 1b                                  \n"
+               "        dsubu  %0, %1, %3                              \n"
+               "       .set    reorder                                 \n"
                "       sync                                            \n"
                "1:                                                     \n"
                "       .set    mips0                                   \n"
@@ -614,7 +623,10 @@ static __inline__ long atomic64_sub_if_p
                "       dsubu   %0, %1, %3                              \n"
                "       bltz    %0, 1f                                  \n"
                "       scd     %0, %2                                  \n"
+               "       .set    noreorder                               \n"
                "       beqz    %0, 1b                                  \n"
+               "        dsubu  %0, %1, %3                              \n"
+               "       .set    reorder                                 \n"
                "       sync                                            \n"
                "1:                                                     \n"
                "       .set    mips0                                   \n"

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