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Date: Tue, 31 Jan 2017 11:27:10 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
eranian@...gle.com, davidcc@...gle.com
Subject: Re: crash in perf_event_read
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.
Reported-by: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: David Carrillo-Cisneros <davidcc@...gle.com>
Cc: Stephane Eranian <eranian@...gle.com>
Fixes: d6a2f9035bfc ("perf/core: Introduce PMU_EV_CAP_READ_ACTIVE_PKG")
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
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;
+
+ 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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