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authorEric Dumazet <eric.dumazet@gmail.com>2011-01-25 17:31:54 +0100
committerIngo Molnar <mingo@elte.hu>2011-01-26 08:10:49 +0100
commit889a7a6a5d5e64063effd40056bdc7b8fb336bd1 (patch)
tree84f366024832785f6eff971c96129be6e131f6c8 /arch/x86/include
parent9a57c3e487d25f69715705dfeef6eb9e4d666ad7 (diff)
downloadlinux-linaro-android-889a7a6a5d5e64063effd40056bdc7b8fb336bd1.tar.gz
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@gmail.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Christoph Lameter <cl@linux-foundation.org> Cc: Tejun Heo <tj@kernel.org> LKML-Reference: <1295973114.3588.312.camel@edumazet-laptop> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86/include')
-rw-r--r--arch/x86/include/asm/percpu.h24
1 files changed, 12 insertions, 12 deletions
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 3788f4649db..7e172955ee5 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; \