Re: [PATCH 1/2] coresight: cti: Initialize dynamic sysfs attributes

[Mathieu Poirier <mathieu.poirier@linaro.org>]

On Thu, Oct 29, 2020 at 08:10:11PM +0100, Greg KH wrote:
> On Thu, Oct 29, 2020 at 10:45:58AM -0600, Mathieu Poirier wrote:
> > From: Suzuki K Poulose <suzuki.poulose@arm.com>
> > 
> > With LOCKDEP enabled, CTI driver triggers the following splat due
> > to uninitialized lock class for dynamically allocated attribute
> > objects.
> > 
> > [    5.372901] coresight etm0: CPU0: ETM v4.0 initialized
> > [    5.376694] coresight etm1: CPU1: ETM v4.0 initialized
> > [    5.380785] coresight etm2: CPU2: ETM v4.0 initialized
> > [    5.385851] coresight etm3: CPU3: ETM v4.0 initialized
> > [    5.389808] BUG: key ffff00000564a798 has not been registered!
> > [    5.392456] ------------[ cut here ]------------
> > [    5.398195] DEBUG_LOCKS_WARN_ON(1)
> > [    5.398233] WARNING: CPU: 1 PID: 32 at kernel/locking/lockdep.c:4623 lockdep_init_map_waits+0x14c/0x260
> > [    5.406149] Modules linked in:
> > [    5.415411] CPU: 1 PID: 32 Comm: kworker/1:1 Not tainted 5.9.0-12034-gbbe85027ce80 #51
> > [    5.418553] Hardware name: Qualcomm Technologies, Inc. APQ 8016 SBC (DT)
> > [    5.426453] Workqueue: events amba_deferred_retry_func
> > [    5.433299] pstate: 40000005 (nZcv daif -PAN -UAO -TCO BTYPE=--)
> > [    5.438252] pc : lockdep_init_map_waits+0x14c/0x260
> > [    5.444410] lr : lockdep_init_map_waits+0x14c/0x260
> > [    5.449007] sp : ffff800012bbb720
> > ...
> > 
> > [    5.531561] Call trace:
> > [    5.536847]  lockdep_init_map_waits+0x14c/0x260
> > [    5.539027]  __kernfs_create_file+0xa8/0x1c8
> > [    5.543539]  sysfs_add_file_mode_ns+0xd0/0x208
> > [    5.548054]  internal_create_group+0x118/0x3c8
> > [    5.552307]  internal_create_groups+0x58/0xb8
> > [    5.556733]  sysfs_create_groups+0x2c/0x38
> > [    5.561160]  device_add+0x2d8/0x768
> > [    5.565148]  device_register+0x28/0x38
> > [    5.568537]  coresight_register+0xf8/0x320
> > [    5.572358]  cti_probe+0x1b0/0x3f0
> > 
> > ...
> > 
> > Fix this by initializing the attributes when they are allocated.
> > 
> > Fixes: 3c5597e39812 ("coresight: cti: Add connection information to sysfs")
> > Reported-by: Leo Yan <leo.yan@linaro.org>
> > Tested-by: Leo Yan <leo.yan@linaro.org>
> > Cc: Mike Leach <mike.leach@linaro.org>
> > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
> > ---
> >  drivers/hwtracing/coresight/coresight-cti-sysfs.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/hwtracing/coresight/coresight-cti-sysfs.c b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > index 392757f3a019..7ff7e7780bbf 100644
> > --- a/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > +++ b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > @@ -1065,6 +1065,13 @@ static int cti_create_con_sysfs_attr(struct device *dev,
> >  	}
> >  	eattr->var = con;
> >  	con->con_attrs[attr_idx] = &eattr->attr.attr;
> > +	/*
> > +	 * Initialize the dynamically allocated attribute
> > +	 * to avoid LOCKDEP splat. See include/linux/sysfs.h
> > +	 * for more details.
> > +	 */
> > +	sysfs_attr_init(con->con_attrs[attr_idx]);
> > +
> >  	return 0;
> >  }
> 
> Should go to stable kernels too, as the patch this fixes is in 5.7.
> I'll add the stable tag here, but feel free to do it yourself next time
> :)

Oh - I (wrongly) assumed all patches with a "Fixes" tag were going to stable. 

> 
> thanks,
> 
> greg k-h