Re: crash in perf_event_read

From: David Carrillo-Cisneros
Date: Thu Feb 02 2017 - 02:43:22 EST

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On Tue, Jan 31, 2017 at 2:27 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Mon, Jan 30, 2017 at 11:04:08PM -0800, Alexei Starovoitov wrote:
>> Hi Peter,
>>
>> rarely I'm seeing the following crash:
>> [40196.164255] BUG: unable to handle kernel paging request at 000000000000a11a
>> [40196.179636] IP: perf_event_read+0xd3/0x1a0
>> [40196.188669] PGD 82e93a067
>> [40196.188670] PUD 7e1ddf067
>> [40196.194629] PMD 0
>> [40196.200589]
>> [40196.208284] Oops: 0000 [#1] SMP
>> [40196.208285] Modules linked in:
>> [40196.208299] CPU: 24 PID: 4423 Comm: dynoKernelMon Not tainted 4.10.0-rc5-01189-gc6e0ad0ee5b0 #599
>> [40196.208300] Hardware name: Quanta Mono Lake-M.2 SATA 20F20BU0270/Mono Lake-M.2 SATA, BIOS F20_3A12 10/24/2016
>> [40196.208301] task: ffff8807e3b65580 task.stack: ffffc90009748000
>> [40196.208302] RIP: 0010:perf_event_read+0xd3/0x1a0
>> [40196.208303] RSP: 0018:ffffc9000974bd48 EFLAGS: 00010202
>> [40196.208304] RAX: 000000000000a040 RBX: ffff8807b79fd000 RCX: 0000000000000000
>> [40196.208304] RDX: 0000000000000018 RSI: 0000000000000000 RDI: 00000000ffffffff
>> [40196.208305] RBP: ffffc9000974bd80 R08: 0000000000000000 R09: 0000000000000000
>> [40196.208305] R10: ffff8807cf8c7038 R11: 0000000000000000 R12: ffffc9000974bde8
>> [40196.208306] R13: 0000000000000000 R14: ffff8807b79fd000 R15: 00000000000004e0
>> [40196.208307] FS: 00007ff1b45ff700(0000) GS:ffff88085f400000(0000) knlGS:0000000000000000
>> [40196.208307] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> [40196.208308] CR2: 000000000000a11a CR3: 0000000850298000 CR4: 00000000003406e0
>> [40196.208308] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> [40196.208309] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> [40196.208309] Call Trace:
>> [40196.208313] ? __might_sleep+0x4a/0x80
>> [40196.208316] perf_event_read_value+0x45/0x130
>> [40196.208318] perf_read+0x84/0x2d0
>> [40196.208322] __vfs_read+0x28/0x110
>> [40196.208325] ? security_file_permission+0x9b/0xc0
>> [40196.208327] vfs_read+0xa5/0x170
>> [40196.208327] SyS_read+0x46/0xa0
>> [40196.208329] do_syscall_64+0x4d/0xb0
>> [40196.208332] entry_SYSCALL64_slow_path+0x25/0x25
>> [40196.208333] RIP: 0033:0x7ff1b6f5716d
>> [40196.208334] RSP: 002b:00007ff1b45fd080 EFLAGS: 00000293 ORIG_RAX: 0000000000000000
>> [40196.208335] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007ff1b6f5716d
>> [40196.208335] RDX: 0000000000000020 RSI: 00007ff1b45fd090 RDI: 0000000000000054
>> [40196.208336] RBP: 00007ff1b45fd0e0 R08: 00007ff1b65e45c0 R09: 00007ff1b45fc9b1
>> [40196.208336] R10: 0000000000000020 R11: 0000000000000293 R12: 0000000000000000
>> [40196.208337] R13: 00007ff1b5687000 R14: 00000004a817c7fe R15: 00000000000004e0
>> [40196.208337] Code: 60 02 00 00 74 30 48 63 cf 48 c7 c0 40 a0 00 00 48 8b 34 cd c0 93 d0 81 48 63 ca 48 8b 0c cd c0 93 d0 81 0f b7 8c 08 da 00 00 00 <66> 39 8c 30 da 00 00 00 0f 44 fa 48 8d 55 d0 b9 01 00 00 00 48
>> [40196.208353] RIP: perf_event_read+0xd3/0x1a0 RSP: ffffc9000974bd48
>> [40196.208353] CR2: 000000000000a11a
>>
>> The RIP points to this asm:
>> 0xffffffff8115fc9b <+155>: mov %gs:0x7eeaa486(%rip),%edx # 0xa128 <cpu_number>
>> 0xffffffff8115fca2 <+162>: testb $0x2,0x68(%rbx)
>> 0xffffffff8115fca6 <+166>: mov 0x260(%rdi),%edi
>> 0xffffffff8115fcac <+172>: je 0xffffffff8115fcde <perf_event_read+222>
>> 0xffffffff8115fcae <+174>: movslq %edi,%rcx
>> 0xffffffff8115fcb1 <+177>: mov $0xa040,%rax
>> 0xffffffff8115fcb8 <+184>: mov -0x7e2f6c40(,%rcx,8),%rsi
>> 0xffffffff8115fcc0 <+192>: movslq %edx,%rcx
>> 0xffffffff8115fcc3 <+195>: mov -0x7e2f6c40(,%rcx,8),%rcx
>> 0xffffffff8115fccb <+203>: movzwl 0xda(%rax,%rcx,1),%ecx
>> 0xffffffff8115fcd3 <+211>: cmp %cx,0xda(%rax,%rsi,1)
>>
>> which is this C code:
>> perf_event_read():
>> local_cpu = get_cpu();
>> cpu_to_read = find_cpu_to_read(event, local_cpu);
>> put_cpu();
>>
>> find_cpu_to_read():
>> event_pkg = topology_physical_package_id(event_cpu);
>> local_pkg = topology_physical_package_id(local_cpu);
>> if (event_pkg == local_pkg)
>>
>> If I read the asm correctly at the time of the crash
>> event_cpu == RDI == 00000000ffffffff
>> or in other words event->oncpu == -1
>> which I think is technically possible here.
>>
>> Any suggestions how to fix this?
>> Happy to test any patches, though I don't know how to reproduce reliably.
>
> Right you are, that's buggered.
>
> Something like the below (compile tested only) ought to cure things I
> think.
>
> ---
> Subject: perf: Fix crash in perf_event_read()
>
> Alexei had his box explode because doing read() on a package
> (rapl/uncore) event that isn't currently scheduled in ends up doing an
> out-of-bounds load.
>
> Rework the code to more explicitly deal with event->oncpu being -1.
>
Tested-by: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
> Reported-by: Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx>
> Cc: David Carrillo-Cisneros <davidcc@xxxxxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Fixes: d6a2f9035bfc ("perf/core: Introduce PMU_EV_CAP_READ_ACTIVE_PKG")
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
> kernel/events/core.c | 23 ++++++++++++++---------
> 1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 88676ff98c0f..8d479be0c9a9 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -3538,14 +3538,15 @@ struct perf_read_data {
> int ret;
> };
>
> -static int find_cpu_to_read(struct perf_event *event, int local_cpu)
> +static int __perf_event_read_cpu(struct perf_event *event, int event_cpu)
> {
> - int event_cpu = event->oncpu;
> u16 local_pkg, event_pkg;
>
> if (event->group_caps & PERF_EV_CAP_READ_ACTIVE_PKG) {
> - event_pkg = topology_physical_package_id(event_cpu);
> - local_pkg = topology_physical_package_id(local_cpu);
> + int local_cpu = smp_processor_id();
> +
> + event_pkg = topology_physical_package_id(event_cpu);
> + local_pkg = topology_physical_package_id(local_cpu);
>
> if (event_pkg == local_pkg)
> return local_cpu;
> @@ -3675,7 +3676,7 @@ u64 perf_event_read_local(struct perf_event *event)
>
> static int perf_event_read(struct perf_event *event, bool group)
> {
> - int ret = 0, cpu_to_read, local_cpu;
> + int event_cpu, ret = 0;
>
> /*
> * If event is enabled and currently active on a CPU, update the
> @@ -3688,9 +3689,12 @@ static int perf_event_read(struct perf_event *event, bool group)
> .ret = 0,
> };
>
> - local_cpu = get_cpu();
> - cpu_to_read = find_cpu_to_read(event, local_cpu);
> - put_cpu();
> + event_cpu = READ_ONCE(event->oncpu);
> + if ((unsigned)event_cpu >= nr_cpu_ids)
> + return 0;

Yeah, I missed that one. Thanks for fixing it.

> +
> + preempt_disable();
> + event_cpu = __perf_event_read_cpu(event, event_cpu);
>
> /*
> * Purposely ignore the smp_call_function_single() return
> @@ -3702,7 +3706,8 @@ static int perf_event_read(struct perf_event *event, bool group)
> * Therefore, either way, we'll have an up-to-date event count
> * after this.
> */
> - (void)smp_call_function_single(cpu_to_read, __perf_event_read, &data, 1);
> + (void)smp_call_function_single(event_cpu, __perf_event_read, &data, 1);
> + preempt_enable();
> ret = data.ret;
> } else if (event->state == PERF_EVENT_STATE_INACTIVE) {
> struct perf_event_context *ctx = event->ctx;

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