[GIT PULL 0/2] stm class/intel_th: Updates for v5.5

[GIT PULL 0/2] stm class/intel_th: Updates for v5.5

[Alexander Shishkin]

Hi Greg,

This is really small, but I'm including a signed tag anyway. These are
a bugfix and a documentation update. The fix is for a bug in v4.20, and
given that it's late -rc7, it makes more sense to me to queue it for the
merge window, but if you think otherwise, as Linus mentioned the
possibility of an -rc8, it's also good. Stable CC'd on the fix.

The following changes since commit 54ecb8f7028c5eb3d740bb82b0f1d90f2df63c5c:

  Linux 5.4-rc1 (2019-09-30 10:35:40 -0700)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/ash/stm.git tags/stm-intel_th-for-greg-20191114

for you to fetch changes up to a5e809f25f41a84b31e17ac9422fb191e2495503:

  intel_th: Document software sinks (2019-11-14 08:20:17 +0200)

----------------------------------------------------------------
stm class/intel_th: Updates for v5.5

These are:
 * a bugfix in stm protocol handling
 * a documentation update for intel_th

----------------------------------------------------------------
Alexander Shishkin (2):
      stm class: Lose the protocol driver when dropping its reference
      intel_th: Document software sinks

 Documentation/trace/intel_th.rst | 28 +++++++++++++++++++++++++++-
 drivers/hwtracing/stm/policy.c   |  4 ++++
 2 files changed, 31 insertions(+), 1 deletion(-)

-- 
2.24.0

[GIT PULL 1/2] stm class: Lose the protocol driver when dropping its reference

[Alexander Shishkin]

Commit c7fd62bc69d02 ("stm class: Introduce framing protocol drivers")
forgot to tear down the link between an stm device and its protocol
driver when policy is removed. This leads to an invalid pointer reference
if one tries to write to an stm device after the policy has been removed
and the protocol driver module unloaded, leading to the below splat:

> BUG: unable to handle page fault for address: ffffffffc0737068
> #PF: supervisor read access in kernel mode
> #PF: error_code(0x0000) - not-present page
> PGD 3d780f067 P4D 3d780f067 PUD 3d7811067 PMD 492781067 PTE 0
> Oops: 0000 [#1] SMP NOPTI
> CPU: 1 PID: 26122 Comm: cat Not tainted 5.4.0-rc5+ #1
> RIP: 0010:stm_output_free+0x40/0xc0 [stm_core]
> Call Trace:
>  stm_char_release+0x3e/0x70 [stm_core]
>  __fput+0xc6/0x260
>  ____fput+0xe/0x10
>  task_work_run+0x9d/0xc0
>  exit_to_usermode_loop+0x103/0x110
>  do_syscall_64+0x19d/0x1e0
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9

Fix this by tearing down the link from an stm device to its protocol
driver when the policy involving that driver is removed.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Fixes: c7fd62bc69d02 ("stm class: Introduce framing protocol drivers")
Reported-by: Ammy Yi <ammy.yi@intel.com>
Tested-by: Ammy Yi <ammy.yi@intel.com>
CC: stable@vger.kernel.org # v4.20+
---
 drivers/hwtracing/stm/policy.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
index 4b9e44b227d8..4f932a419752 100644
--- a/drivers/hwtracing/stm/policy.c
+++ b/drivers/hwtracing/stm/policy.c
@@ -345,7 +345,11 @@ void stp_policy_unbind(struct stp_policy *policy)
 	stm->policy = NULL;
 	policy->stm = NULL;
 
+	/*
+	 * Drop the reference on the protocol driver and lose the link.
+	 */
 	stm_put_protocol(stm->pdrv);
+	stm->pdrv = NULL;
 	stm_put_device(stm);
 }
 
-- 
2.24.0

[GIT PULL 2/2] intel_th: Document software sinks

[Alexander Shishkin]

Add documentation for the software sinks API of the MSU driver and the
msu-sink module in particular.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
 Documentation/trace/intel_th.rst | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/Documentation/trace/intel_th.rst b/Documentation/trace/intel_th.rst
index baa12eb09ef4..70b7126eaeeb 100644
--- a/Documentation/trace/intel_th.rst
+++ b/Documentation/trace/intel_th.rst
@@ -44,7 +44,8 @@ Documentation/trace/stm.rst for more information on that.
 
 MSU can be configured to collect trace data into a system memory
 buffer, which can later on be read from its device nodes via read() or
-mmap() interface.
+mmap() interface and directed to a "software sink" driver that will
+consume the data and/or relay it further.
 
 On the whole, Intel(R) Trace Hub does not require any special
 userspace software to function; everything can be configured, started
@@ -122,3 +123,28 @@ In order to enable the host mode, set the 'host_mode' parameter of the
 will show up on the intel_th bus. Also, trace configuration and
 capture controlling attribute groups of the 'gth' device will not be
 exposed. The 'sth' device will operate as usual.
+
+Software Sinks
+--------------
+
+The Memory Storage Unit (MSU) driver provides an in-kernel API for
+drivers to register themselves as software sinks for the trace data.
+Such drivers can further export the data via other devices, such as
+USB device controllers or network cards.
+
+The API has two main parts::
+ - notifying the software sink that a particular window is full, and
+   "locking" that window, that is, making it unavailable for the trace
+   collection; when this happens, the MSU driver will automatically
+   switch to the next window in the buffer if it is unlocked, or stop
+   the trace capture if it's not;
+ - tracking the "locked" state of windows and providing a way for the
+   software sink driver to notify the MSU driver when a window is
+   unlocked and can be used again to collect trace data.
+
+An example sink driver, msu-sink illustrates the implementation of a
+software sink. Functionally, it simply unlocks windows as soon as they
+are full, keeping the MSU running in a circular buffer mode. Unlike the
+"multi" mode, it will fill out all the windows in the buffer as opposed
+to just the first one. It can be enabled by writing "sink" to the "mode"
+file (assuming msu-sink.ko is loaded).
-- 
2.24.0

Re: [GIT PULL 0/2] stm class/intel_th: Updates for v5.5

[Greg Kroah-Hartman]

On Thu, Nov 14, 2019 at 08:41:59AM +0200, Alexander Shishkin wrote:
> Hi Greg,
> 
> This is really small, but I'm including a signed tag anyway. These are
> a bugfix and a documentation update. The fix is for a bug in v4.20, and
> given that it's late -rc7, it makes more sense to me to queue it for the
> merge window, but if you think otherwise, as Linus mentioned the
> possibility of an -rc8, it's also good. Stable CC'd on the fix.
> 
> The following changes since commit 54ecb8f7028c5eb3d740bb82b0f1d90f2df63c5c:
> 
>   Linux 5.4-rc1 (2019-09-30 10:35:40 -0700)
> 
> are available in the Git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/ash/stm.git tags/stm-intel_th-for-greg-20191114
> 
> for you to fetch changes up to a5e809f25f41a84b31e17ac9422fb191e2495503:

Looks good, I've taken these as patches, thanks.

greg k-h