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Date: Wed, 30 Sep 2009 21:32:04 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Arjan van de Ven <arjan@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Eric Dumazet <eric.dumazet@...il.com>,
Martin Schwidefsky <schwidefsky@...ibm.com>,
Thomas Gleixner <tglx@...utronix.de>,
John Stultz <johnstul@...ibm.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: Linux 2.6.32-rc1
* Arjan van de Ven <arjan@...radead.org> wrote:
> From 5a76986c5dd272ea16a9b8abb7349ff3d6791c2b Mon Sep 17 00:00:00 2001
> From: Arjan van de Ven <arjan@...ux.intel.com>
> Date: Wed, 30 Sep 2009 17:04:35 +0200
> Subject: [PATCH] x86: Provide an alternative() based cmpxchg64()
>
> Based on Linus' patch, this patch provides cmpxchg64() using
> the alternative() infrastructure.
>
> Note: the fallback is NOT smp safe, just like the current fallback
> is not SMP safe.
>
> Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
> ---
> arch/x86/include/asm/cmpxchg_32.h | 29 ++++++++++--------
> arch/x86/kernel/i386_ksyms_32.c | 3 ++
> arch/x86/lib/Makefile | 2 +-
> arch/x86/lib/cmpxchg8b_emu.S | 61 +++++++++++++++++++++++++++++++++++++
> 4 files changed, 81 insertions(+), 14 deletions(-)
> create mode 100644 arch/x86/lib/cmpxchg8b_emu.S
The two patches cause hangs on 32-bit, in sched_clock_cpu(). I attached
the hang serial log plus the two patches as i applied them.
Bug in cmpxchg8b_emu()?
Ingo
[ 45.800000] i2c-core: driver [tw9910] registered
[ 45.810000] initcall tw9910_module_init+0x0/0x2e returned 0 after 9765 usecs
[ 45.810000] BUG: spinlock lockup on CPU#1, swapper/1, 7be09ec0
[ 45.810000] Pid: 1, comm: swapper Tainted: G W 2.6.32-rc2-tip-00990-g6139d57-dirty #19124
[ 45.810000] Call Trace:
[ 45.810000] [<79ebce42>] ? printk+0x22/0x35
[ 45.810000] [<794356c7>] _raw_spin_lock+0x103/0x13f
[ 45.810000] [<79ebf84d>] _spin_lock+0x3c/0x55
[ 45.810000] [<790673e0>] ? scheduler_tick+0x44/0x20e
[ 45.810000] [<790673e0>] scheduler_tick+0x44/0x20e
[ 45.810000] [<790793fc>] update_process_times+0x4a/0x68
[ 45.810000] [<7909354c>] tick_periodic+0x7a/0x8d
[ 45.810000] [<79093588>] tick_handle_periodic+0x29/0x91
[ 45.810000] [<7909398f>] tick_do_broadcast+0x42/0x7d
[ 45.810000] [<79093b17>] tick_do_periodic_broadcast+0x3c/0x59
[ 45.810000] [<79093fb0>] tick_handle_periodic_broadcast+0x20/0x70
[ 45.810000] [<7902fac1>] timer_interrupt+0x4d/0x85
[ 45.810000] [<790ab402>] handle_IRQ_event+0x65/0x13b
[ 45.810000] [<790ad1fc>] handle_edge_irq+0xbe/0x111
[ 45.810000] [<7902f553>] handle_irq+0x2f/0x46
[ 45.810000] [<7902ee8b>] do_IRQ+0x51/0xb8
[ 45.810000] [<7902d435>] common_interrupt+0x35/0x40
[ 45.810000] [<7906afe2>] ? vprintk+0x3a8/0x3fa
[ 45.810000] [<79090020>] ? ntp_clear+0x22/0x7d
[ 45.810000] [<79ebdf6c>] ? __mutex_unlock_slowpath+0x10e/0x12f
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<79ebce42>] printk+0x22/0x35
[ 45.810000] [<790010ed>] do_one_initcall+0xc4/0x183
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<7a562474>] do_basic_setup+0x50/0x72
[ 45.810000] [<7a562509>] kernel_init+0x73/0xc5
[ 45.810000] [<7a562496>] ? kernel_init+0x0/0xc5
[ 45.810000] [<7902d997>] kernel_thread_helper+0x7/0x10
[ 45.810000] sending NMI to all CPUs:
[ 45.810000] NMI backtrace for cpu 1
[ 45.810000]
[ 45.810000] Pid: 1, comm: swapper Tainted: G W (2.6.32-rc2-tip-00990-g6139d57-dirty #19124) System Product Name
[ 45.810000] EIP: 0060:[<79097b38>] EFLAGS: 00000046 CPU: 1
[ 45.810000] EIP is at trace_hardirqs_off_caller+0x3f/0xbd
[ 45.810000] EAX: 82f26dd9 EBX: b78c8000 ECX: 00000000 EDX: 790412fc
[ 45.810000] ESI: 790412fc EDI: 00000002 EBP: b78c3d10 ESP: b78c3d04
[ 45.810000] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[ 45.810000] CR0: 8005003b CR2: 00000000 CR3: 02664000 CR4: 00000690
[ 45.810000] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[ 45.810000] DR6: ffff0ff0 DR7: 00000400
[ 45.810000] Call Trace:
[ 45.810000] [<79097bcf>] trace_hardirqs_off+0x19/0x2c
[ 45.810000] [<790412fc>] default_send_IPI_mask_logical+0x8f/0xb1
[ 45.810000] [<79041084>] default_send_IPI_all+0x35/0x87
[ 45.810000] [<790416bc>] arch_trigger_all_cpu_backtrace+0x40/0x73
[ 45.810000] [<794356cc>] _raw_spin_lock+0x108/0x13f
[ 45.810000] [<79ebf84d>] _spin_lock+0x3c/0x55
[ 45.810000] [<790673e0>] ? scheduler_tick+0x44/0x20e
[ 45.810000] [<790673e0>] scheduler_tick+0x44/0x20e
[ 45.810000] [<790793fc>] update_process_times+0x4a/0x68
[ 45.810000] [<7909354c>] tick_periodic+0x7a/0x8d
[ 45.810000] [<79093588>] tick_handle_periodic+0x29/0x91
[ 45.810000] [<7909398f>] tick_do_broadcast+0x42/0x7d
[ 45.810000] [<79093b17>] tick_do_periodic_broadcast+0x3c/0x59
[ 45.810000] [<79093fb0>] tick_handle_periodic_broadcast+0x20/0x70
[ 45.810000] [<7902fac1>] timer_interrupt+0x4d/0x85
[ 45.810000] [<790ab402>] handle_IRQ_event+0x65/0x13b
[ 45.810000] [<790ad1fc>] handle_edge_irq+0xbe/0x111
[ 45.810000] [<7902f553>] handle_irq+0x2f/0x46
[ 45.810000] [<7902ee8b>] do_IRQ+0x51/0xb8
[ 45.810000] [<7902d435>] common_interrupt+0x35/0x40
[ 45.810000] [<7906afe2>] ? vprintk+0x3a8/0x3fa
[ 45.810000] [<79090020>] ? ntp_clear+0x22/0x7d
[ 45.810000] [<79ebdf6c>] ? __mutex_unlock_slowpath+0x10e/0x12f
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<79ebce42>] printk+0x22/0x35
[ 45.810000] [<790010ed>] do_one_initcall+0xc4/0x183
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<7a562474>] do_basic_setup+0x50/0x72
[ 45.810000] [<7a562509>] kernel_init+0x73/0xc5
[ 45.810000] [<7a562496>] ? kernel_init+0x0/0xc5
[ 45.810000] [<7902d997>] kernel_thread_helper+0x7/0x10
[ 45.810000] Pid: 1, comm: swapper Tainted: G W 2.6.32-rc2-tip-00990-g6139d57-dirty #19124
[ 45.810000] Call Trace:
[ 45.810000] [<7902bce1>] ? show_regs+0x34/0x4b
[ 45.810000] [<7904188d>] nmi_watchdog_tick+0xa4/0x181
[ 45.810000] [<7902e941>] default_do_nmi+0x64/0x21e
[ 45.810000] [<790412fc>] ? default_send_IPI_mask_logical+0x8f/0xb1
[ 45.810000] [<7902eb5d>] do_nmi+0x62/0xad
[ 45.810000] [<79ec0080>] nmi_stack_correct+0x2f/0x34
[ 45.810000] [<790412fc>] ? default_send_IPI_mask_logical+0x8f/0xb1
[ 45.810000] [<790412fc>] ? default_send_IPI_mask_logical+0x8f/0xb1
[ 45.810000] [<79097b38>] ? trace_hardirqs_off_caller+0x3f/0xbd
[ 45.810000] [<79097bcf>] trace_hardirqs_off+0x19/0x2c
[ 45.810000] [<790412fc>] default_send_IPI_mask_logical+0x8f/0xb1
[ 45.810000] [<79041084>] default_send_IPI_all+0x35/0x87
[ 45.810000] [<790416bc>] arch_trigger_all_cpu_backtrace+0x40/0x73
[ 45.810000] [<794356cc>] _raw_spin_lock+0x108/0x13f
[ 45.810000] [<79ebf84d>] _spin_lock+0x3c/0x55
[ 45.810000] [<790673e0>] ? scheduler_tick+0x44/0x20e
[ 45.810000] [<790673e0>] scheduler_tick+0x44/0x20e
[ 45.810000] [<790793fc>] update_process_times+0x4a/0x68
[ 45.810000] [<7909354c>] tick_periodic+0x7a/0x8d
[ 45.810000] [<79093588>] tick_handle_periodic+0x29/0x91
[ 45.810000] [<7909398f>] tick_do_broadcast+0x42/0x7d
[ 45.810000] [<79093b17>] tick_do_periodic_broadcast+0x3c/0x59
[ 45.810000] [<79093fb0>] tick_handle_periodic_broadcast+0x20/0x70
[ 45.810000] [<7902fac1>] timer_interrupt+0x4d/0x85
[ 45.810000] [<790ab402>] handle_IRQ_event+0x65/0x13b
[ 45.810000] [<790ad1fc>] handle_edge_irq+0xbe/0x111
[ 45.810000] [<7902f553>] handle_irq+0x2f/0x46
[ 45.810000] [<7902ee8b>] do_IRQ+0x51/0xb8
[ 45.810000] [<7902d435>] common_interrupt+0x35/0x40
[ 45.810000] [<7906afe2>] ? vprintk+0x3a8/0x3fa
[ 45.810000] [<79090020>] ? ntp_clear+0x22/0x7d
[ 45.810000] [<79ebdf6c>] ? __mutex_unlock_slowpath+0x10e/0x12f
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<79ebce42>] printk+0x22/0x35
[ 45.810000] [<790010ed>] do_one_initcall+0xc4/0x183
[ 45.810000] [<7a5ab658>] ? tw9910_module_init+0x0/0x2e
[ 45.810000] [<7a562474>] do_basic_setup+0x50/0x72
[ 45.810000] [<7a562509>] kernel_init+0x73/0xc5
[ 45.810000] [<7a562496>] ? kernel_init+0x0/0xc5
[ 45.810000] [<7902d997>] kernel_thread_helper+0x7/0x10
[ 45.810000] NMI backtrace for cpu 0
[ 45.810000]
[ 45.810000] Pid: 0, comm: swapper Tainted: G W (2.6.32-rc2-tip-00990-g6139d57-dirty #19124) System Product Name
[ 45.810000] EIP: 0060:[<7908c649>] EFLAGS: 00000086 CPU: 0
[ 45.810000] EIP is at sched_clock_cpu+0x120/0x159
[ 45.810000] EAX: aa7d20b2 EBX: aa7d20b2 ECX: 0000000a EDX: 0000000a
[ 45.810000] ESI: 7be0a450 EDI: 00000001 EBP: 7a42de1c ESP: 7a42ddd8
[ 45.810000] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[ 45.810000] CR0: 8005003b CR2: ffcff000 CR3: 02664000 CR4: 00000690
[ 45.810000] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[ 45.810000] DR6: ffff0ff0 DR7: 00000400
[ 45.810000] Call Trace:
[ 45.810000] [<7905f54b>] update_rq_clock+0x24/0x45
[ 45.810000] [<7905f5d3>] double_rq_lock+0x67/0x7d
[ 45.810000] [<79066bc4>] load_balance+0x116/0x355
[ 45.810000] [<79098b07>] ? trace_hardirqs_on_caller+0x106/0x159
[ 45.810000] [<79066ec6>] rebalance_domains+0xc3/0x134
[ 45.810000] [<79066f78>] run_rebalance_domains+0x41/0xc2
[ 45.810000] [<79071154>] __do_softirq+0xd2/0x1a0
[ 45.810000] [<79071260>] do_softirq+0x3e/0x68
[ 45.810000] [<79071423>] irq_exit+0x4b/0x9f
[ 45.810000] [<790409e3>] smp_apic_timer_interrupt+0x81/0xa0
[ 45.810000] [<7902d7f6>] apic_timer_interrupt+0x36/0x40
[ 45.810000] [<7903377c>] ? test_ti_thread_flag+0x1/0x30
[ 45.810000] [<79033878>] ? need_resched+0x27/0x42
[ 45.810000] [<790338c2>] poll_idle+0x2f/0x76
[ 45.810000] [<7902bd98>] cpu_idle+0xa0/0xd4
[ 45.810000] [<79e2b392>] rest_init+0x7a/0x8d
[ 45.810000] [<7a562ab2>] start_kernel+0x33a/0x350
[ 45.810000] [<7a56209f>] i386_start_kernel+0x9f/0xb5
[ 45.810000] Pid: 0, comm: swapper Tainted: G W 2.6.32-rc2-tip-00990-g6139d57-dirty #19124
[ 45.810000] Call Trace:
[ 45.810000] [<7902bce1>] ? show_regs+0x34/0x4b
[ 45.810000] [<7904188d>] nmi_watchdog_tick+0xa4/0x181
[ 45.810000] [<7902e941>] default_do_nmi+0x64/0x21e
[ 45.810000] [<7902eb5d>] do_nmi+0x62/0xad
[ 45.810000] [<79ec0080>] nmi_stack_correct+0x2f/0x34
[ 45.810000] [<7908c649>] ? sched_clock_cpu+0x120/0x159
[ 45.810000] [<7905f54b>] update_rq_clock+0x24/0x45
[ 45.810000] [<7905f5d3>] double_rq_lock+0x67/0x7d
[ 45.810000] [<79066bc4>] load_balance+0x116/0x355
[ 45.810000] [<79098b07>] ? trace_hardirqs_on_caller+0x106/0x159
[ 45.810000] [<79066ec6>] rebalance_domains+0xc3/0x134
[ 45.810000] [<79066f78>] run_rebalance_domains+0x41/0xc2
[ 45.810000] [<79071154>] __do_softirq+0xd2/0x1a0
[ 45.810000] [<79071260>] do_softirq+0x3e/0x68
[ 45.810000] [<79071423>] irq_exit+0x4b/0x9f
[ 45.810000] [<790409e3>] smp_apic_timer_interrupt+0x81/0xa0
[ 45.810000] [<7902d7f6>] apic_timer_interrupt+0x36/0x40
[ 45.810000] [<7903377c>] ? test_ti_thread_flag+0x1/0x30
[ 45.810000] [<79033878>] ? need_resched+0x27/0x42
[ 45.810000] [<790338c2>] poll_idle+0x2f/0x76
[ 45.810000] [<7902bd98>] cpu_idle+0xa0/0xd4
[ 45.810000] [<79e2b392>] rest_init+0x7a/0x8d
[ 45.810000] [<7a562ab2>] start_kernel+0x33a/0x350
[ 45.810000] [<7a56209f>] i386_start_kernel+0x9f/0xb5
commit 1cb9955464ad248c79c48e9c8be6669020fe178c
Author: Arjan van de Ven <arjan@...radead.org>
Date: Wed Sep 30 20:36:19 2009 +0200
sched_clock: Fix atomicity/continuity bug by using cmpxchg64()
Commit def0a9b2573 (sched_clock: Make it NMI safe) assumed
cmpxchg() of 64bit values was available on X86_32.
That is not so - and causes some subtle scheduler misbehavior due
to incorrect timestamps off to up by ~4 seconds.
Two symptoms are known right now:
- interactivity problems seen by Arjan: up to 600 msecs
latencies instead of the expected 20-40 msecs. These
latencies are very visible on the desktop.
- incorrect CPU stats: occasionally too high percentages in 'top',
and crazy CPU usage stats.
Reported-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: John Stultz <johnstul@...ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <20090930170754.0886ff2e@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
diff --git a/kernel/sched_clock.c b/kernel/sched_clock.c
index ac2e1dc..479ce56 100644
--- a/kernel/sched_clock.c
+++ b/kernel/sched_clock.c
@@ -127,7 +127,7 @@ again:
clock = wrap_max(clock, min_clock);
clock = wrap_min(clock, max_clock);
- if (cmpxchg(&scd->clock, old_clock, clock) != old_clock)
+ if (cmpxchg64(&scd->clock, old_clock, clock) != old_clock)
goto again;
return clock;
@@ -163,7 +163,7 @@ again:
val = remote_clock;
}
- if (cmpxchg(ptr, old_val, val) != old_val)
+ if (cmpxchg64(ptr, old_val, val) != old_val)
goto again;
return val;
commit 8da752098d4e584fbcc149046e5c716f5d356db4
Author: Arjan van de Ven <arjan@...radead.org>
Date: Wed Sep 30 17:07:54 2009 +0200
x86: Provide an alternative() based cmpxchg64()
cmpxchg64() today generates, to quote Linus, "barf bag" code.
cmpxchg64() is about to get used in the scheduler to a bug there,
but it's a prerequisite that cmpxchg64() first be made non-sucking.
This patch turns cmpxchg64() into an efficient implementation that
uses the alternative() mechanism to just use the raw instruction on
all modern systens
Note: the fallback is NOT smp safe, just like the current fallback
is not SMP safe. (Interested parties with i486 based SMP systems
are welcome to submit fix patches for that.)
Signed-off-by: Arjan van de Ven <arjan@...ux.intel.com>
Acked-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Eric Dumazet <eric.dumazet@...il.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: John Stultz <johnstul@...ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <20090930170754.0886ff2e@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index 82ceb78..3b21afa 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -312,19 +312,22 @@ static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old,
extern unsigned long long cmpxchg_486_u64(volatile void *, u64, u64);
-#define cmpxchg64(ptr, o, n) \
-({ \
- __typeof__(*(ptr)) __ret; \
- if (likely(boot_cpu_data.x86 > 4)) \
- __ret = (__typeof__(*(ptr)))__cmpxchg64((ptr), \
- (unsigned long long)(o), \
- (unsigned long long)(n)); \
- else \
- __ret = (__typeof__(*(ptr)))cmpxchg_486_u64((ptr), \
- (unsigned long long)(o), \
- (unsigned long long)(n)); \
- __ret; \
-})
+#define cmpxchg64(ptr, o, n) \
+({ \
+ __typeof__(*(ptr)) __ret; \
+ __typeof__(*(ptr)) __old = (o); \
+ __typeof__(*(ptr)) __new = (n); \
+ alternative_io("call cmpxchg8b_emu", \
+ "lock; cmpxchg8b (%%esi)" , \
+ X86_FEATURE_CX8, \
+ "=A" (__ret), \
+ "S" ((ptr)), "0" (__old), \
+ "b" ((unsigned int)__new), \
+ "c" ((unsigned int)(__new>>32))); \
+ __ret; })
+
+
+
#define cmpxchg64_local(ptr, o, n) \
({ \
__typeof__(*(ptr)) __ret; \
diff --git a/arch/x86/kernel/i386_ksyms_32.c b/arch/x86/kernel/i386_ksyms_32.c
index 43cec6b..1736c5a 100644
--- a/arch/x86/kernel/i386_ksyms_32.c
+++ b/arch/x86/kernel/i386_ksyms_32.c
@@ -10,6 +10,14 @@
EXPORT_SYMBOL(mcount);
#endif
+/*
+ * Note, this is a prototype to get at the symbol for
+ * the export, but dont use it from C code, it is used
+ * by assembly code and is not using C calling convention!
+ */
+extern void cmpxchg8b_emu(void);
+EXPORT_SYMBOL(cmpxchg8b_emu);
+
/* Networking helper routines. */
EXPORT_SYMBOL(csum_partial_copy_generic);
diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 9e60920..3e549b8 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -15,7 +15,7 @@ ifeq ($(CONFIG_X86_32),y)
obj-y += atomic64_32.o
lib-y += checksum_32.o
lib-y += strstr_32.o
- lib-y += semaphore_32.o string_32.o
+ lib-y += semaphore_32.o string_32.o cmpxchg8b_emu.o
lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
else
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
new file mode 100644
index 0000000..b8af4c7
--- /dev/null
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -0,0 +1,61 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ *
+ */
+
+#include <linux/linkage.h>
+#include <asm/alternative-asm.h>
+#include <asm/frame.h>
+#include <asm/dwarf2.h>
+
+
+.text
+
+/*
+ * Inputs:
+ * %esi : memory location to compare
+ * %eax : low 32 bits of old value
+ * %edx : high 32 bits of old value
+ * %ebx : low 32 bits of new value
+ * %ecx : high 32 bits of new value
+ */
+ENTRY(cmpxchg8b_emu)
+ CFI_STARTPROC
+
+ push %edi
+ push %ebx
+ push %ecx
+ /* disable interrupts */
+ pushf
+ pop %edi
+ cli
+
+ cmpl %edx, 4(%esi)
+ jne 1f
+ cmpl %eax, (%esi)
+ jne 1f
+
+ xchg (%esi), %ebx
+ xchg 4(%esi), %ecx
+ mov %ebx, %eax
+ mov %ecx, %edx
+
+2:
+ /* restore interrupts */
+ push %edi
+ popf
+
+ pop %ecx
+ pop %ebx
+ pop %edi
+ ret
+1:
+ mov (%esi), %eax
+ mov 4(%esi), %edx
+ jmp 2b
+ CFI_ENDPROC
+ENDPROC(cmpxchg8b_emu)
+
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