Subject: Re: [PATCH v3] coresight: fix missing error code when trace ID is invalid

From: Richard Cheng <[email-masked]>
Date: Mon, 11 May 2026 18:26:54 +0800

On Mon, May 11, 2026 at 05:27:10PM +0800, Jie Gan wrote:
> 
> 
> On 5/11/2026 5:19 PM, Richard Cheng wrote:
> > On Mon, May 11, 2026 at 04:36:18PM +0800, Jie Gan wrote:
> > > When coresight_path_assign_trace_id() cannot assign a valid trace ID,
> > > coresight_enable_sysfs() takes the err_path goto with ret still 0,
> > > returning success to the caller despite no trace session being started.
> > > 
> > > Fix this by changing coresight_path_assign_trace_id() to return int.
> > > Move the IS_VALID_CS_TRACE_ID() check inside the function so it returns
> > > -EINVAL on failure and 0 on success. Update coresight_enable_sysfs() to
> > > check the return value directly instead of inspecting path->trace_id
> > > after the call.
> > > 
> > > The other caller in coresight-etm-perf.c discards the return value and
> > > continues to check path->trace_id via IS_VALID_CS_TRACE_ID() directly.
> > > This is unaffected: on failure path->trace_id is no longer written, so
> > > it remains 0, which IS_VALID_CS_TRACE_ID() rejects the same as before.
> > > 
> > > Fixes: d87d76d823d1 ("Coresight: Allocate trace ID after building the path")
> > > Reviewed-by: James Clark <[email-masked]>
> > > Signed-off-by: Jie Gan <[email-masked]>
> > > ---
> > > Changes in v3:
> > > - directly return the value for clear expression.
> > > - Link to v2: https://lore.kernel.org/r/[email-masked]
> > > 
> > > Changes in v2:
> > > - Refactor the coresight_path_assign_trace_id function.
> > > - Link to v1: https://lore.kernel.org/r/[email-masked]
> > > ---
> > >   drivers/hwtracing/coresight/coresight-core.c  | 14 ++++++++++----
> > >   drivers/hwtracing/coresight/coresight-priv.h  |  2 +-
> > >   drivers/hwtracing/coresight/coresight-sysfs.c |  4 ++--
> > >   3 files changed, 13 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> > > index 46f247f73cf6..254db91a8ac9 100644
> > > --- a/drivers/hwtracing/coresight/coresight-core.c
> > > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > > @@ -739,8 +739,8 @@ static int coresight_get_trace_id(struct coresight_device *csdev,
> > >    * Call this after creating the path and before enabling it. This leaves
> > >    * the trace ID set on the path, or it remains 0 if it couldn't be assigned.
> > >    */
> > > -void coresight_path_assign_trace_id(struct coresight_path *path,
> > > -				    enum cs_mode mode)
> > > +int coresight_path_assign_trace_id(struct coresight_path *path,
> > > +				   enum cs_mode mode)
> > >   {
> > >   	struct coresight_device *sink = coresight_get_sink(path);
> > >   	struct coresight_node *nd;
> > > @@ -755,10 +755,16 @@ void coresight_path_assign_trace_id(struct coresight_path *path,
> > >   		 * Non 0 is either success or fail.
> > >   		 */
> > >   		if (trace_id != 0) {
> > > -			path->trace_id = trace_id;
> > > -			return;
> > > +			if (IS_VALID_CS_TRACE_ID(trace_id)) {
> > > +				path->trace_id = trace_id;
> > > +				return 0;
> > > +			}
> > > +
> > > +			return -EINVAL;
> > >   		}
> > >   	}
> > > +
> > > +	return -EINVAL;
> > >   }
> > >   /**
> > > diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> > > index 1ea882dffd70..34c7e792adbd 100644
> > > --- a/drivers/hwtracing/coresight/coresight-priv.h
> > > +++ b/drivers/hwtracing/coresight/coresight-priv.h
> > > @@ -153,7 +153,7 @@ int coresight_make_links(struct coresight_device *orig,
> > >   void coresight_remove_links(struct coresight_device *orig,
> > >   			    struct coresight_connection *conn);
> > >   u32 coresight_get_sink_id(struct coresight_device *csdev);
> > > -void coresight_path_assign_trace_id(struct coresight_path *path,
> > > +int coresight_path_assign_trace_id(struct coresight_path *path,
> > >   				   enum cs_mode mode);
> > 
> > Hi Jie,
> > 
> > Thanks for your patch,
> > 
> > I'm thinking will "__must_check" should be added so in the future the next caller won't accidently
> > introduce this class of bug ?
> > 
> 
> Hi Richard,
> 
> The return value has been ignored in perf mode. It will introduce noisy by
> adding __must_check. So I think its better without __must_check?
> 
> Thanks,
> Jie
>

Hi Jie,

Ahh thanks for the head up, my intention was adding a compile-time check there
to be safe, no need for __must_check here then.

If any new callers were to appear in the future we'll see how it goes.
Thanks.

Reviewed-by: Richard Cheng <[email-masked]>

Best regards,
Richard Cheng.
 
> > Best regards,
> > Richard Cheng.
> > 
> > >   #if IS_ENABLED(CONFIG_CORESIGHT_SOURCE_ETM3X)
> > > diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
> > > index d2a6ed8bcc74..b6a870399e83 100644
> > > --- a/drivers/hwtracing/coresight/coresight-sysfs.c
> > > +++ b/drivers/hwtracing/coresight/coresight-sysfs.c
> > > @@ -211,8 +211,8 @@ int coresight_enable_sysfs(struct coresight_device *csdev)
> > >   		goto out;
> > >   	}
> > > -	coresight_path_assign_trace_id(path, CS_MODE_SYSFS);
> > > -	if (!IS_VALID_CS_TRACE_ID(path->trace_id))
> > > +	ret = coresight_path_assign_trace_id(path, CS_MODE_SYSFS);
> > > +	if (ret)
> > >   		goto err_path;
> > >   	ret = coresight_enable_path(path, CS_MODE_SYSFS);
> > > 
> > > ---
> > > base-commit: 17c7841d09ee7d33557fd075562d9289b6018c90
> > > change-id: 20260508-fix-trace-id-error-dbfdd4d8f2d1
> > > 
> > > Best regards,
> > > -- 
> > > Jie Gan <[email-masked]>
> > > 
> > > 
>