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Date: Wed, 26 Jan 2011 07:26:47 GMT
From: tip-bot for Eric Dumazet <eric.dumazet@...il.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, acme@...hat.com, hpa@...or.com,
mingo@...hat.com, eric.dumazet@...il.com, a.p.zijlstra@...llo.nl,
torvalds@...ux-foundation.org, fweisbec@...il.com,
rostedt@...dmis.org, tj@...nel.org, tglx@...utronix.de,
mingo@...e.hu, cl@...ux-foundation.org
Subject: [tip:x86/urgent] percpu, x86: Fix percpu_xchg_op()
Commit-ID: 889a7a6a5d5e64063effd40056bdc7b8fb336bd1
Gitweb: http://git.kernel.org/tip/889a7a6a5d5e64063effd40056bdc7b8fb336bd1
Author: Eric Dumazet <eric.dumazet@...il.com>
AuthorDate: Tue, 25 Jan 2011 17:31:54 +0100
Committer: Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 26 Jan 2011 08:10:49 +0100
percpu, x86: Fix percpu_xchg_op()
These recent percpu commits:
2485b6464cf8: x86,percpu: Move out of place 64 bit ops into X86_64 section
8270137a0d50: cpuops: Use cmpxchg for xchg to avoid lock semantics
Caused this 'perf top' crash:
Kernel panic - not syncing: Fatal exception in interrupt
Pid: 0, comm: swapper Tainted: G D
2.6.38-rc2-00181-gef71723 #413 Call Trace: <IRQ> [<ffffffff810465b5>]
? panic
? kmsg_dump
? kmsg_dump
? oops_end
? no_context
? __bad_area_nosemaphore
? perf_output_begin
? bad_area_nosemaphore
? do_page_fault
? __task_pid_nr_ns
? perf_event_tid
? __perf_event_header__init_id
? validate_chain
? perf_output_sample
? trace_hardirqs_off
? page_fault
? irq_work_run
? update_process_times
? tick_sched_timer
? tick_sched_timer
? __run_hrtimer
? hrtimer_interrupt
? account_system_vtime
? smp_apic_timer_interrupt
? apic_timer_interrupt
...
Looking at assembly code, I found:
list = this_cpu_xchg(irq_work_list, NULL);
gives this wrong code : (gcc-4.1.2 cross compiler)
ffffffff810bc45e:
mov %gs:0xead0,%rax
cmpxchg %rax,%gs:0xead0
jne ffffffff810bc45e <irq_work_run+0x3e>
test %rax,%rax
je ffffffff810bc4aa <irq_work_run+0x8a>
Tell gcc we dirty eax/rax register in percpu_xchg_op()
Compiler must use another register to store pxo_new__
We also dont need to reload percpu value after a jump,
since a 'failed' cmpxchg already updated eax/rax
Wrong generated code was :
xor %rax,%rax /* load 0 into %rax */
1: mov %gs:0xead0,%rax
cmpxchg %rax,%gs:0xead0
jne 1b
test %rax,%rax
After patch :
xor %rdx,%rdx /* load 0 into %rdx */
mov %gs:0xead0,%rax
1: cmpxchg %rdx,%gs:0xead0
jne 1b:
test %rax,%rax
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Christoph Lameter <cl@...ux-foundation.org>
Cc: Tejun Heo <tj@...nel.org>
LKML-Reference: <1295973114.3588.312.camel@...mazet-laptop>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
arch/x86/include/asm/percpu.h | 24 ++++++++++++------------
1 files changed, 12 insertions(+), 12 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 3788f46..7e17295 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -273,34 +273,34 @@ do { \
typeof(var) pxo_new__ = (nval); \
switch (sizeof(var)) { \
case 1: \
- asm("\n1:mov "__percpu_arg(1)",%%al" \
- "\n\tcmpxchgb %2, "__percpu_arg(1) \
+ asm("\n\tmov "__percpu_arg(1)",%%al" \
+ "\n1:\tcmpxchgb %2, "__percpu_arg(1) \
"\n\tjnz 1b" \
- : "=a" (pxo_ret__), "+m" (var) \
+ : "=&a" (pxo_ret__), "+m" (var) \
: "q" (pxo_new__) \
: "memory"); \
break; \
case 2: \
- asm("\n1:mov "__percpu_arg(1)",%%ax" \
- "\n\tcmpxchgw %2, "__percpu_arg(1) \
+ asm("\n\tmov "__percpu_arg(1)",%%ax" \
+ "\n1:\tcmpxchgw %2, "__percpu_arg(1) \
"\n\tjnz 1b" \
- : "=a" (pxo_ret__), "+m" (var) \
+ : "=&a" (pxo_ret__), "+m" (var) \
: "r" (pxo_new__) \
: "memory"); \
break; \
case 4: \
- asm("\n1:mov "__percpu_arg(1)",%%eax" \
- "\n\tcmpxchgl %2, "__percpu_arg(1) \
+ asm("\n\tmov "__percpu_arg(1)",%%eax" \
+ "\n1:\tcmpxchgl %2, "__percpu_arg(1) \
"\n\tjnz 1b" \
- : "=a" (pxo_ret__), "+m" (var) \
+ : "=&a" (pxo_ret__), "+m" (var) \
: "r" (pxo_new__) \
: "memory"); \
break; \
case 8: \
- asm("\n1:mov "__percpu_arg(1)",%%rax" \
- "\n\tcmpxchgq %2, "__percpu_arg(1) \
+ asm("\n\tmov "__percpu_arg(1)",%%rax" \
+ "\n1:\tcmpxchgq %2, "__percpu_arg(1) \
"\n\tjnz 1b" \
- : "=a" (pxo_ret__), "+m" (var) \
+ : "=&a" (pxo_ret__), "+m" (var) \
: "r" (pxo_new__) \
: "memory"); \
break; \
--
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