Re: Linux 2.6.32-rc1

Eric Dumazet
2009-09-30T20:16:42Z

Ingo Molnar a écrit :
> * Arjan van de Ven <arjan@infradead.org> wrote:
>
>> From 5a76986c5dd272ea16a9b8abb7349ff3d6791c2b Mon Sep 17 00:00:00 2001
>> From: Arjan van de Ven <arjan@linux.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@linux.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@infradead.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@de.ibm.com>
> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
> Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
> Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: John Stultz <johnstul@us.ibm.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> LKML-Reference: <20090930170754.0886ff2e@infradead.org>
> Signed-off-by: Ingo Molnar <mingo@elte.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@infradead.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@linux.intel.com>
> Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>
> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Cc: John Stultz <johnstul@us.ibm.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> LKML-Reference: <20090930170754.0886ff2e@infradead.org>
> Signed-off-by: Ingo Molnar <mingo@elte.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))); \

probably a "memory" clobber is needed, alternative_io() doesnt provide it.

> + __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)
> +
>