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Subject: Re: [PATCH] coresight: Fix crash when Perf and sysfs modes are used
 concurrently
To:     Suzuki K Poulose <suzuki.poulose@arm.com>,
        James Clark <james.clark@arm.com>, <coresight@lists.linaro.org>
References: <20231006131452.646721-1-james.clark@arm.com>
 <b6050a3f-d464-6b0a-dc79-18103dd7d527@arm.com>
CC:     Mike Leach <mike.leach@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
From:   hejunhao <hejunhao3@huawei.com>
Message-ID: <a51751e5-7f6b-3910-66bd-5018c0ced9f0@huawei.com>
Date:   Tue, 10 Oct 2023 10:43:42 +0800
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On 2023/10/9 20:27, Suzuki K Poulose wrote:
> Junhao He,
>
> Please could you test the patch and let us know if it resolves the
> problem for you ?

Hi James and Suzuki ,

I tested the patch on my platform and it worked well.

>
> On 06/10/2023 14:14, James Clark wrote:
>> Partially revert the change in commit 6148652807ba ("coresight: Enable
>> and disable helper devices adjacent to the path") which changed the bare
>> call from source_ops(csdev)->enable() to coresight_enable_source() for
>> Perf sessions. It was missed that coresight_enable_source() is
>> specifically for the sysfs interface, rather than being a generic call.
>> This interferes with the sysfs reference counting to cause the following
>> crash:
>>
>>    $ perf record -e cs_etm/@tmc_etr0/ -C 0 &
>>    $ echo 1 > /sys/bus/coresight/devices/tmc_etr0/enable_sink
>>    $ echo 1 > /sys/bus/coresight/devices/etm0/enable_source
>>    $ echo 0 > /sys/bus/coresight/devices/etm0/enable_source
>>
>>    Unable to handle kernel NULL pointer dereference at virtual
>>    address 00000000000001d0
>>    Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
>>    ...
>>    Call trace:
>>     etm4_disable+0x54/0x150 [coresight_etm4x]
>>     coresight_disable_source+0x6c/0x98 [coresight]
>>     coresight_disable+0x74/0x1c0 [coresight]
>>     enable_source_store+0x88/0xa0 [coresight]
>>     dev_attr_store+0x20/0x40
>>     sysfs_kf_write+0x4c/0x68
>>     kernfs_fop_write_iter+0x120/0x1b8
>>     vfs_write+0x2dc/0x3b0
>>     ksys_write+0x70/0x108
>>     __arm64_sys_write+0x24/0x38
>>     invoke_syscall+0x50/0x128
>>     el0_svc_common.constprop.0+0x104/0x130
>>     do_el0_svc+0x40/0xb8
>>     el0_svc+0x2c/0xb8
>>     el0t_64_sync_handler+0xc0/0xc8
>>     el0t_64_sync+0x1a4/0x1a8
>>    Code: d53cd042 91002000 b9402a81 b8626800 (f940ead5)
>>    ---[ end trace 0000000000000000 ]---
>>
>> This commit linked below also fixes the issue, but has unlocked updates
>> to the mode which could potentially race. So until we come up with a
>> more complete solution that takes all locking and interaction between
>> both modes into account, just revert back to the old behavior for Perf.
>>
>> Reported-by: Junhao He <hejunhao3@huawei.com>
>> Closes: 
>> https://lore.kernel.org/linux-arm-kernel/20230921132904.60996-1-hejunhao3@huawei.com/
>> Fixes: 6148652807ba ("coresight: Enable and disable helper devices 
>> adjacent to the path")
>> Signed-off-by: James Clark <james.clark@arm.com>
>
> The patch looks good to me. I will wait for Junhao to test this before
> pulling it in.
>
> Suzuki
>

Tested-by: Junhao He <hejunhao3@huawei.com>

Thanks.
Junhao.

>
>
>
>> ---
>>   drivers/hwtracing/coresight/coresight-etm-perf.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c 
>> b/drivers/hwtracing/coresight/coresight-etm-perf.c
>> index 5ca6278baff4..89e8ed214ea4 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
>> @@ -493,7 +493,7 @@ static void etm_event_start(struct perf_event 
>> *event, int flags)
>>           goto fail_end_stop;
>>         /* Finally enable the tracer */
>> -    if (coresight_enable_source(csdev, CS_MODE_PERF, event))
>> +    if (source_ops(csdev)->enable(csdev, event, CS_MODE_PERF))
>>           goto fail_disable_path;
>>         /*
>> @@ -587,7 +587,7 @@ static void etm_event_stop(struct perf_event 
>> *event, int mode)
>>           return;
>>         /* stop tracer */
>> -    coresight_disable_source(csdev, event);
>> +    source_ops(csdev)->disable(csdev, event);
>>         /* tell the core */
>>       event->hw.state = PERF_HES_STOPPED;
>
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