linux-kernel - Re: [PATCH 0/9] coresight: change some driver' spinlock type to raw_spinlock

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Message-ID: <22ef761d-7a9c-46a2-8d61-3d16c2188c0c@linaro.org>
Date: Wed, 27 Nov 2024 16:44:50 +0000
From: James Clark <james.clark@...aro.org>
To: Yeoreum Yun <yeoreum.yun@....com>, suzuki.poulose@....com,
 mike.leach@...aro.org
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-rt-devel@...ts.linux.dev, nd@....com,
 alexander.shishkin@...ux.intel.com, bigeasy@...utronix.de,
 clrkwllms@...nel.org, rostedt@...dmis.org
Subject: Re: [PATCH 0/9] coresight: change some driver' spinlock type to
 raw_spinlock_t



On 25/11/2024 9:48 am, Yeoreum Yun wrote:
> In some coresight drivers, drvdata->spinlock can be held during __schedule()
> by perf_event_task_sched_out()/in().
> 
> Since drvdata->spinlock type is spinlock_t and
> perf_event_task_sched_out()/in() is called after acquiring rq_lock,
> which is raw_spinlock_t (an unsleepable lock),
> this poses an issue in PREEMPT_RT kernel where spinlock_t is sleepable.
> 
> To address this,change type drvdata->spinlock in some coresight drivers,
> which can be called by perf_event_task_sched_out()/in(),
> from spinlock_t to raw_spinlock_t.
> 
> Levi Yun (9):
>    coresight: change coresight_device lock type to raw_spinlock_t
>    coresight-etm4x: change etmv4_drvdata spinlock type to raw_spinlock_t
>    coresight: change coresight_trace_id_map's lock type to raw_spinlock_t
>    coresight-cti: change cti_drvdata spinlock's type to raw_spinlock_t
>    coresight-etb10: change etb_drvdata spinlock's type to raw_spinlock_t
>    coresight-funnel: change funnel_drvdata spinlock's type to
>      raw_spinlock_t
>    coresight-replicator: change replicator_drvdata spinlock's type to
>      raw_spinlock_t
>    coresight-tmc: change tmc_drvdata spinlock's type to raw_spinlock_t
>    coresight/ultrasoc: change cti_drvdata spinlock's type to
>      raw_spinlock_t
> 
>   .../hwtracing/coresight/coresight-config.c    |  21 +-
>   .../hwtracing/coresight/coresight-config.h    |   2 +-
>   drivers/hwtracing/coresight/coresight-core.c  |   2 +-
>   .../hwtracing/coresight/coresight-cti-core.c  |  65 +-
>   .../hwtracing/coresight/coresight-cti-sysfs.c | 135 +++--
>   drivers/hwtracing/coresight/coresight-cti.h   |   2 +-
>   drivers/hwtracing/coresight/coresight-etb10.c |  62 +-
>   .../coresight/coresight-etm4x-core.c          |  71 ++-
>   .../coresight/coresight-etm4x-sysfs.c         | 566 +++++++++---------
>   drivers/hwtracing/coresight/coresight-etm4x.h |   2 +-
>   .../hwtracing/coresight/coresight-funnel.c    |  34 +-
>   .../coresight/coresight-replicator.c          |  36 +-
>   .../hwtracing/coresight/coresight-syscfg.c    |  75 ++-
>   .../hwtracing/coresight/coresight-tmc-core.c  |   9 +-
>   .../hwtracing/coresight/coresight-tmc-etf.c   | 195 +++---
>   .../hwtracing/coresight/coresight-tmc-etr.c   | 199 +++---
>   drivers/hwtracing/coresight/coresight-tmc.h   |   2 +-
>   .../hwtracing/coresight/coresight-trace-id.c  |  93 ++-
>   drivers/hwtracing/coresight/ultrasoc-smb.c    |  12 +-
>   drivers/hwtracing/coresight/ultrasoc-smb.h    |   2 +-
>   include/linux/coresight.h                     |   4 +-
>   21 files changed, 751 insertions(+), 838 deletions(-)
> 
> --
> LEVI:{C3F47F37-75D8-414A-A8BA-3980EC8A46D7}
> 

Reviewed-by: James Clark <james.clark@...aro.org>

Somewhat related to this change, but not something that needs to be done 
now:

All of the spinlocks for the syfs store/read functions don't need to be 
raw spinlocks, or spinlocks at all. They're never called from the 
scheduling code and can be locked by coresight_mutex instead. 
coresight_mutex is held on the sysfs enable/disable path when those 
values are actually used.

Same point as here: 
https://lore.kernel.org/linux-arm-kernel/9a637e74-d81d-405c-bad0-c97ec1aa4b77@linaro.org/

Probably needs a review of which values in each device might be shared 
between perf mode and sysfs mode when they shouldn't be, as there was 
one in the link above.

I thought the only thing shared between sysfs and perf should be the 
'mode' which is taken with a compare and swap without locking anyway.