* Re: [PATCH v2 1/3] Documentation: adopt new coding style of type-aware kmalloc-family
From: Matthew Wilcox @ 2026-04-21 19:24 UTC (permalink / raw)
To: Manuel Ebner
Cc: Jonathan Corbet, Shuah Khan, linux-doc, Kees Cook, linux-kernel,
workflows, linux-sound, linux-media
In-Reply-To: <20260421180200.225244-2-manuelebner@mailbox.org>
On Tue, Apr 21, 2026 at 08:01:58PM +0200, Manuel Ebner wrote:
> +++ b/Documentation/core-api/memory-allocation.rst
> @@ -135,7 +135,7 @@ Selecting memory allocator
> The most straightforward way to allocate memory is to use a function
> from the kmalloc() family. And, to be on the safe side it's best to use
> routines that set memory to zero, like kzalloc(). If you need to
> -allocate memory for an array, there are kmalloc_array() and kcalloc()
> +allocate memory for an array, there are kmalloc_objs() and kzalloc_objs()
> helpers. The helpers struct_size(), array_size() and array3_size() can
> be used to safely calculate object sizes without overflowing.
This seems to have been done without any thought. kmalloc_array() still
exists and has over 500 callers. It should not be de-documented.
> @@ -151,7 +151,7 @@ sizes, the alignment is guaranteed to be at least the largest power-of-two
> divisor of the size.
>
> Chunks allocated with kmalloc() can be resized with krealloc(). Similarly
> -to kmalloc_array(): a helper for resizing arrays is provided in the form of
> +to kmalloc_objs(): a helper for resizing arrays is provided in the form of
> krealloc_array().
Think about why this is wrong too.
And you should have cc'd linux-mm on this.
^ permalink raw reply
* [PATCH v2 3/3] Documentation: deprecated.rst: kmalloc-family: mark argument as optional
From: Manuel Ebner @ 2026-04-21 18:09 UTC (permalink / raw)
To: Jonathan Corbet, Shuah Khan, linux-doc, Kees Cook, linux-kernel
Cc: workflows, Manuel Ebner
In-Reply-To: <20260421175516.224960-2-manuelebner@mailbox.org>
put the optional argument (gfp) in square brackets
eg. ptr = kmalloc_obj(*ptr, gfp);
-> ptr = kmalloc_obj(*ptr, [gfp]);
Signed-off-by: Manuel Ebner <manuelebner@mailbox.org>
---
Documentation/process/deprecated.rst | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
index fed56864d036..b431993fd08e 100644
--- a/Documentation/process/deprecated.rst
+++ b/Documentation/process/deprecated.rst
@@ -392,12 +392,12 @@ allocations. For example, these open coded assignments::
become, respectively::
- ptr = kmalloc_obj(*ptr, gfp);
- ptr = kzalloc_obj(*ptr, gfp);
- ptr = kmalloc_objs(*ptr, count, gfp);
- ptr = kzalloc_objs(*ptr, count, gfp);
- ptr = kmalloc_flex(*ptr, flex_member, count, gfp);
- __auto_type ptr = kmalloc_obj(struct foo, gfp);
+ ptr = kmalloc_obj(*ptr, [gfp]);
+ ptr = kzalloc_obj(*ptr, [gfp]);
+ ptr = kmalloc_objs(*ptr, count, [gfp]);
+ ptr = kzalloc_objs(*ptr, count, [gfp]);
+ ptr = kmalloc_flex(*ptr, flex_member, count, [gfp]);
+ __auto_type ptr = kmalloc_obj(struct foo, [gfp]);
If `ptr->flex_member` is annotated with __counted_by(), the allocation
will automatically fail if `count` is larger than the maximum
--
2.53.0
^ permalink raw reply related
* [PATCH v2 1/3] Documentation: adopt new coding style of type-aware kmalloc-family
From: Manuel Ebner @ 2026-04-21 18:01 UTC (permalink / raw)
To: Jonathan Corbet, Shuah Khan, linux-doc
Cc: Kees Cook, linux-kernel, workflows, linux-sound, linux-media,
Manuel Ebner
In-Reply-To: <20260421175516.224960-2-manuelebner@mailbox.org>
Update the documentation to reflect new type-aware kmalloc-family as
suggested in commit 2932ba8d9c99 ("slab: Introduce kmalloc_obj() and family")
ptr = kmalloc(sizeof(*ptr), gfp);
-> ptr = kmalloc_obj(*ptr);
ptr = kmalloc(sizeof(struct some_obj_name), gfp);
-> ptr = kmalloc_obj(*ptr);
ptr = kzalloc(sizeof(*ptr), gfp);
-> ptr = kzalloc_obj(*ptr);
ptr = kmalloc_array(count, sizeof(*ptr), gfp);
-> ptr = kmalloc_objs(*ptr, count);
ptr = kcalloc(count, sizeof(*ptr), gfp);
-> ptr = kzalloc_objs(*ptr, count);
Signed-off-by: Manuel Ebner <manuelebner@mailbox.org>
---
Documentation/core-api/kref.rst | 4 ++--
Documentation/core-api/list.rst | 4 ++--
Documentation/core-api/memory-allocation.rst | 4 ++--
Documentation/driver-api/mailbox.rst | 4 ++--
Documentation/driver-api/media/v4l2-fh.rst | 2 +-
Documentation/kernel-hacking/locking.rst | 4 ++--
Documentation/locking/locktypes.rst | 4 ++--
Documentation/process/coding-style.rst | 8 ++++----
.../sound/kernel-api/writing-an-alsa-driver.rst | 12 ++++++------
Documentation/spi/spi-summary.rst | 4 ++--
.../translations/it_IT/kernel-hacking/locking.rst | 4 ++--
.../translations/it_IT/locking/locktypes.rst | 4 ++--
.../translations/it_IT/process/coding-style.rst | 2 +-
.../translations/sp_SP/process/coding-style.rst | 2 +-
Documentation/translations/zh_CN/core-api/kref.rst | 4 ++--
.../translations/zh_CN/process/coding-style.rst | 2 +-
.../zh_CN/video4linux/v4l2-framework.txt | 2 +-
.../translations/zh_TW/process/coding-style.rst | 2 +-
18 files changed, 36 insertions(+), 36 deletions(-)
diff --git a/Documentation/core-api/kref.rst b/Documentation/core-api/kref.rst
index 8db9ff03d952..1c14c036699d 100644
--- a/Documentation/core-api/kref.rst
+++ b/Documentation/core-api/kref.rst
@@ -40,7 +40,7 @@ kref_init as so::
struct my_data *data;
- data = kmalloc(sizeof(*data), GFP_KERNEL);
+ data = kmalloc_obj(*data);
if (!data)
return -ENOMEM;
kref_init(&data->refcount);
@@ -100,7 +100,7 @@ thread to process::
int rv = 0;
struct my_data *data;
struct task_struct *task;
- data = kmalloc(sizeof(*data), GFP_KERNEL);
+ data = kmalloc_obj(*data);
if (!data)
return -ENOMEM;
kref_init(&data->refcount);
diff --git a/Documentation/core-api/list.rst b/Documentation/core-api/list.rst
index 241464ca0549..86cd0a1b77ea 100644
--- a/Documentation/core-api/list.rst
+++ b/Documentation/core-api/list.rst
@@ -112,7 +112,7 @@ list:
/* State 1 */
- grock = kzalloc(sizeof(*grock), GFP_KERNEL);
+ grock = kzalloc_obj(*grock);
if (!grock)
return -ENOMEM;
grock->name = "Grock";
@@ -123,7 +123,7 @@ list:
/* State 2 */
- dimitri = kzalloc(sizeof(*dimitri), GFP_KERNEL);
+ dimitri = kzalloc_obj(*dimitri);
if (!dimitri)
return -ENOMEM;
dimitri->name = "Dimitri";
diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst
index 0f19dd524323..8379775f17d3 100644
--- a/Documentation/core-api/memory-allocation.rst
+++ b/Documentation/core-api/memory-allocation.rst
@@ -135,7 +135,7 @@ Selecting memory allocator
The most straightforward way to allocate memory is to use a function
from the kmalloc() family. And, to be on the safe side it's best to use
routines that set memory to zero, like kzalloc(). If you need to
-allocate memory for an array, there are kmalloc_array() and kcalloc()
+allocate memory for an array, there are kmalloc_objs() and kzalloc_objs()
helpers. The helpers struct_size(), array_size() and array3_size() can
be used to safely calculate object sizes without overflowing.
@@ -151,7 +151,7 @@ sizes, the alignment is guaranteed to be at least the largest power-of-two
divisor of the size.
Chunks allocated with kmalloc() can be resized with krealloc(). Similarly
-to kmalloc_array(): a helper for resizing arrays is provided in the form of
+to kmalloc_objs(): a helper for resizing arrays is provided in the form of
krealloc_array().
For large allocations you can use vmalloc() and vzalloc(), or directly
diff --git a/Documentation/driver-api/mailbox.rst b/Documentation/driver-api/mailbox.rst
index 463dd032b96c..4bcd73a99115 100644
--- a/Documentation/driver-api/mailbox.rst
+++ b/Documentation/driver-api/mailbox.rst
@@ -87,8 +87,8 @@ a message and a callback function to the API and return immediately).
struct async_pkt ap;
struct sync_pkt sp;
- dc_sync = kzalloc(sizeof(*dc_sync), GFP_KERNEL);
- dc_async = kzalloc(sizeof(*dc_async), GFP_KERNEL);
+ dc_sync = kzalloc_obj(*dc_sync);
+ dc_async = kzalloc_obj(*dc_async);
/* Populate non-blocking mode client */
dc_async->cl.dev = &pdev->dev;
diff --git a/Documentation/driver-api/media/v4l2-fh.rst b/Documentation/driver-api/media/v4l2-fh.rst
index a934caa483a4..38319130ebf5 100644
--- a/Documentation/driver-api/media/v4l2-fh.rst
+++ b/Documentation/driver-api/media/v4l2-fh.rst
@@ -42,7 +42,7 @@ Example:
...
- my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL);
+ my_fh = kzalloc_obj(*my_fh);
...
diff --git a/Documentation/kernel-hacking/locking.rst b/Documentation/kernel-hacking/locking.rst
index dff0646a717b..d02e62367c4f 100644
--- a/Documentation/kernel-hacking/locking.rst
+++ b/Documentation/kernel-hacking/locking.rst
@@ -442,7 +442,7 @@ to protect the cache and all the objects within it. Here's the code::
{
struct object *obj;
- if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL)
+ if ((obj = kmalloc_obj(*obj)) == NULL)
return -ENOMEM;
strscpy(obj->name, name, sizeof(obj->name));
@@ -517,7 +517,7 @@ which are taken away, and the ``+`` are lines which are added.
struct object *obj;
+ unsigned long flags;
- if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL)
+ if ((obj = kmalloc_obj(*obj)) == NULL)
return -ENOMEM;
@@ -63,30 +64,33 @@
obj->id = id;
diff --git a/Documentation/locking/locktypes.rst b/Documentation/locking/locktypes.rst
index 37b6a5670c2f..ac1ad722a9e7 100644
--- a/Documentation/locking/locktypes.rst
+++ b/Documentation/locking/locktypes.rst
@@ -498,7 +498,7 @@ allocating memory. Thus, on a non-PREEMPT_RT kernel the following code
works perfectly::
raw_spin_lock(&lock);
- p = kmalloc(sizeof(*p), GFP_ATOMIC);
+ p = kmalloc_obj(*p, GFP_ATOMIC);
But this code fails on PREEMPT_RT kernels because the memory allocator is
fully preemptible and therefore cannot be invoked from truly atomic
@@ -507,7 +507,7 @@ while holding normal non-raw spinlocks because they do not disable
preemption on PREEMPT_RT kernels::
spin_lock(&lock);
- p = kmalloc(sizeof(*p), GFP_ATOMIC);
+ p = kmalloc_obj(*p, GFP_ATOMIC);
bit spinlocks
diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
index 35b381230f6e..a3bf75dc7c88 100644
--- a/Documentation/process/coding-style.rst
+++ b/Documentation/process/coding-style.rst
@@ -936,7 +936,7 @@ used.
---------------------
The kernel provides the following general purpose memory allocators:
-kmalloc(), kzalloc(), kmalloc_array(), kcalloc(), vmalloc(), and
+kmalloc(), kzalloc(), kmalloc_objs(), kzalloc_objs(), vmalloc(), and
vzalloc(). Please refer to the API documentation for further information
about them. :ref:`Documentation/core-api/memory-allocation.rst
<memory_allocation>`
@@ -945,7 +945,7 @@ The preferred form for passing a size of a struct is the following:
.. code-block:: c
- p = kmalloc(sizeof(*p), ...);
+ p = kmalloc_obj(*p, ...);
The alternative form where struct name is spelled out hurts readability and
introduces an opportunity for a bug when the pointer variable type is changed
@@ -959,13 +959,13 @@ The preferred form for allocating an array is the following:
.. code-block:: c
- p = kmalloc_array(n, sizeof(...), ...);
+ p = kmalloc_objs(*ptr, n, ...);
The preferred form for allocating a zeroed array is the following:
.. code-block:: c
- p = kcalloc(n, sizeof(...), ...);
+ p = kzalloc_objs(*ptr, n, ...);
Both forms check for overflow on the allocation size n * sizeof(...),
and return NULL if that occurred.
diff --git a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
index 895752cbcedd..12433612aa9c 100644
--- a/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
+++ b/Documentation/sound/kernel-api/writing-an-alsa-driver.rst
@@ -266,7 +266,7 @@ to details explained in the following section.
....
/* allocate a chip-specific data with zero filled */
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ chip = kzalloc_obj(*chip);
if (chip == NULL)
return -ENOMEM;
@@ -628,7 +628,7 @@ After allocating a card instance via :c:func:`snd_card_new()`
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
0, &card);
.....
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ chip = kzalloc_obj(*chip);
The chip record should have the field to hold the card pointer at least,
@@ -747,7 +747,7 @@ destructor and PCI entries. Example code is shown first, below::
return -ENXIO;
}
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ chip = kzalloc_obj(*chip);
if (chip == NULL) {
pci_disable_device(pci);
return -ENOMEM;
@@ -1737,7 +1737,7 @@ callback::
{
struct my_pcm_data *data;
....
- data = kmalloc(sizeof(*data), GFP_KERNEL);
+ data = kmalloc_obj(*data);
substream->runtime->private_data = data;
....
}
@@ -3301,7 +3301,7 @@ You can then pass any pointer value to the ``private_data``. If you
assign private data, you should define a destructor, too. The
destructor function is set in the ``private_free`` field::
- struct mydata *p = kmalloc(sizeof(*p), GFP_KERNEL);
+ struct mydata *p = kmalloc_obj(*p);
hw->private_data = p;
hw->private_free = mydata_free;
@@ -3833,7 +3833,7 @@ chip data individually::
err = snd_card_new(&pci->dev, index[dev], id[dev], THIS_MODULE,
0, &card);
....
- chip = kzalloc(sizeof(*chip), GFP_KERNEL);
+ chip = kzalloc_obj(*chip);
....
card->private_data = chip;
....
diff --git a/Documentation/spi/spi-summary.rst b/Documentation/spi/spi-summary.rst
index 6e21e6f86912..7ad6af76c247 100644
--- a/Documentation/spi/spi-summary.rst
+++ b/Documentation/spi/spi-summary.rst
@@ -249,7 +249,7 @@ And SOC-specific utility code might look something like::
{
struct mysoc_spi_data *pdata2;
- pdata2 = kmalloc(sizeof *pdata2, GFP_KERNEL);
+ pdata2 = kmalloc_obj(*pdata2);
*pdata2 = pdata;
...
if (n == 2) {
@@ -373,7 +373,7 @@ a bus (appearing under /sys/class/spi_master).
return -ENODEV;
/* get memory for driver's per-chip state */
- chip = kzalloc(sizeof *chip, GFP_KERNEL);
+ chip = kzalloc(*chip);
if (!chip)
return -ENOMEM;
spi_set_drvdata(spi, chip);
diff --git a/Documentation/translations/it_IT/kernel-hacking/locking.rst b/Documentation/translations/it_IT/kernel-hacking/locking.rst
index 4c21cf60f775..acca89a3743a 100644
--- a/Documentation/translations/it_IT/kernel-hacking/locking.rst
+++ b/Documentation/translations/it_IT/kernel-hacking/locking.rst
@@ -462,7 +462,7 @@ e tutti gli oggetti che contiene. Ecco il codice::
{
struct object *obj;
- if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL)
+ if ((obj = kmalloc_obj(*obj)) == NULL)
return -ENOMEM;
strscpy(obj->name, name, sizeof(obj->name));
@@ -537,7 +537,7 @@ sono quelle rimosse, mentre quelle ``+`` sono quelle aggiunte.
struct object *obj;
+ unsigned long flags;
- if ((obj = kmalloc(sizeof(*obj), GFP_KERNEL)) == NULL)
+ if ((obj = kmalloc_obj(*obj)) == NULL)
return -ENOMEM;
@@ -63,30 +64,33 @@
obj->id = id;
diff --git a/Documentation/translations/it_IT/locking/locktypes.rst b/Documentation/translations/it_IT/locking/locktypes.rst
index 1c7056283b9d..d5fa36aa05cc 100644
--- a/Documentation/translations/it_IT/locking/locktypes.rst
+++ b/Documentation/translations/it_IT/locking/locktypes.rst
@@ -488,7 +488,7 @@ o rwlock_t. Per esempio, la sezione critica non deve fare allocazioni di
memoria. Su un kernel non-PREEMPT_RT il seguente codice funziona perfettamente::
raw_spin_lock(&lock);
- p = kmalloc(sizeof(*p), GFP_ATOMIC);
+ p = kmalloc_obj(*p, GFP_ATOMIC);
Ma lo stesso codice non funziona su un kernel PREEMPT_RT perché l'allocatore di
memoria può essere oggetto di prelazione e quindi non può essere chiamato in un
@@ -497,7 +497,7 @@ trattiene un blocco *non-raw* perché non disabilitano la prelazione sui kernel
PREEMPT_RT::
spin_lock(&lock);
- p = kmalloc(sizeof(*p), GFP_ATOMIC);
+ p = kmalloc_obj(*p, GFP_ATOMIC);
bit spinlocks
diff --git a/Documentation/translations/it_IT/process/coding-style.rst b/Documentation/translations/it_IT/process/coding-style.rst
index c0dc786b8474..2a499412a2e3 100644
--- a/Documentation/translations/it_IT/process/coding-style.rst
+++ b/Documentation/translations/it_IT/process/coding-style.rst
@@ -943,7 +943,7 @@ Il modo preferito per passare la dimensione di una struttura è il seguente:
.. code-block:: c
- p = kmalloc(sizeof(*p), ...);
+ p = kmalloc_obj(*p, ...);
La forma alternativa, dove il nome della struttura viene scritto interamente,
peggiora la leggibilità e introduce possibili bachi quando il tipo di
diff --git a/Documentation/translations/sp_SP/process/coding-style.rst b/Documentation/translations/sp_SP/process/coding-style.rst
index 7d63aa8426e6..44c93d5f6beb 100644
--- a/Documentation/translations/sp_SP/process/coding-style.rst
+++ b/Documentation/translations/sp_SP/process/coding-style.rst
@@ -955,7 +955,7 @@ La forma preferida para pasar el tamaño de una estructura es la siguiente:
.. code-block:: c
- p = kmalloc(sizeof(*p), ...);
+ p = kmalloc_obj(*p, ...);
La forma alternativa donde se deletrea el nombre de la estructura perjudica
la legibilidad, y presenta una oportunidad para un error cuando se cambia
diff --git a/Documentation/translations/zh_CN/core-api/kref.rst b/Documentation/translations/zh_CN/core-api/kref.rst
index b9902af310c5..fcff01e99852 100644
--- a/Documentation/translations/zh_CN/core-api/kref.rst
+++ b/Documentation/translations/zh_CN/core-api/kref.rst
@@ -52,7 +52,7 @@ kref可以出现在数据结构体中的任何地方。
struct my_data *data;
- data = kmalloc(sizeof(*data), GFP_KERNEL);
+ data = kmalloc_obj(*data);
if (!data)
return -ENOMEM;
kref_init(&data->refcount);
@@ -106,7 +106,7 @@ Kref规则
int rv = 0;
struct my_data *data;
struct task_struct *task;
- data = kmalloc(sizeof(*data), GFP_KERNEL);
+ data = kmalloc_obj(*data);
if (!data)
return -ENOMEM;
kref_init(&data->refcount);
diff --git a/Documentation/translations/zh_CN/process/coding-style.rst b/Documentation/translations/zh_CN/process/coding-style.rst
index 5a342a024c01..55d5da974d89 100644
--- a/Documentation/translations/zh_CN/process/coding-style.rst
+++ b/Documentation/translations/zh_CN/process/coding-style.rst
@@ -813,7 +813,7 @@ Documentation/translations/zh_CN/core-api/memory-allocation.rst 。
.. code-block:: c
- p = kmalloc(sizeof(*p), ...);
+ p = kmalloc_obj(*p, ...);
另外一种传递方式中，sizeof 的操作数是结构体的名字，这样会降低可读性，并且可能
会引入 bug。有可能指针变量类型被改变时，而对应的传递给内存分配函数的 sizeof
diff --git a/Documentation/translations/zh_CN/video4linux/v4l2-framework.txt b/Documentation/translations/zh_CN/video4linux/v4l2-framework.txt
index f0be21a60a0f..ba43c5c4797c 100644
--- a/Documentation/translations/zh_CN/video4linux/v4l2-framework.txt
+++ b/Documentation/translations/zh_CN/video4linux/v4l2-framework.txt
@@ -799,7 +799,7 @@ int my_open(struct file *file)
...
- my_fh = kzalloc(sizeof(*my_fh), GFP_KERNEL);
+ my_fh = kzalloc_obj(*my_fh);
...
diff --git a/Documentation/translations/zh_TW/process/coding-style.rst b/Documentation/translations/zh_TW/process/coding-style.rst
index e2ba97b3d8bb..63c78982a1af 100644
--- a/Documentation/translations/zh_TW/process/coding-style.rst
+++ b/Documentation/translations/zh_TW/process/coding-style.rst
@@ -827,7 +827,7 @@ Documentation/translations/zh_CN/core-api/memory-allocation.rst 。
.. code-block:: c
- p = kmalloc(sizeof(*p), ...);
+ p = kmalloc_obj(*p, ...);
另外一種傳遞方式中，sizeof 的操作數是結構體的名字，這樣會降低可讀性，並且可能
會引入 bug。有可能指針變量類型被改變時，而對應的傳遞給內存分配函數的 sizeof
--
2.53.0
^ permalink raw reply related
* [PATCH v2 0/3] Documentation: adopt new coding style of type-aware kmalloc-family
From: Manuel Ebner @ 2026-04-21 17:55 UTC (permalink / raw)
To: Jonathan Corbet, Shuah Khan, linux-doc, Kees Cook
Cc: linux-kernel, workflows, linux-sound, rcu, linux-media,
Manuel Ebner
Update the documentation to reflect new type-aware kmalloc-family as
suggested in commit 2932ba8d9c99 ("slab: Introduce kmalloc_obj() and family")
I have also thought about adding a few cases to checkpatch.pl, but this
will take me some time, and i don't know if i can do it.
[v1] -> [v2]:
put RCU/* in a seperate patch [Patch 2/3]
Omit optional argument (GFP_KERNEL) as suggested by https://lwn.net/Articles/1062856/
deprecated.rst: change the argument gfp to optional [Patch 3/3]
Signed-off-by: Manuel Ebner <manuelebner@mailbox.org>
^ permalink raw reply
* Re: [PATCH] Documentation: adopt new coding style of type-aware kmalloc-family
From: Kees Cook @ 2026-04-21 17:25 UTC (permalink / raw)
To: Jonathan Corbet
Cc: Manuel Ebner, Shuah Khan, linux-doc, lrcu, linux-kernel,
workflows, linux-sound, rcu, linux-media
In-Reply-To: <87se8rw8df.fsf@trenco.lwn.net>
On Sun, Apr 19, 2026 at 04:29:48AM -0600, Jonathan Corbet wrote:
> Manuel Ebner <manuelebner@mailbox.org> writes:
>
> > Update the documentation to reflect new type-aware kmalloc-family as
> > suggested in commit 2932ba8d9c99 ("slab: Introduce kmalloc_obj() and family")
> >
> > ptr = kmalloc(sizeof(*ptr), gfp);
> > -> ptr = kmalloc_obj(*ptr, gfp);
> > ptr = kmalloc(sizeof(struct some_obj_name), gfp);
> > -> ptr = kmalloc_obj(*ptr, gfp);
> > ptr = kzalloc(sizeof(*ptr), gfp);
> > -> ptr = kzalloc_obj(*ptr, gfp);
> > ptr = kmalloc_array(count, sizeof(*ptr), gfp);
> > -> ptr = kmalloc_objs(*ptr, count, gfp);
> > ptr = kcalloc(count, sizeof(*ptr), gfp);
> > -> ptr = kzalloc_objs(*ptr, count, gfp);
> >
> > Signed-off-by: Manuel Ebner <manuelebner@mailbox.org>
>
> Just to be sure, did you write this patch yourself, or did you use some
> sort of coding assistant?
>
> Adding Kees, who did this work and might have something to add here.
>
> > ---
> > .../RCU/Design/Requirements/Requirements.rst | 6 +++---
> > Documentation/RCU/listRCU.rst | 2 +-
> > Documentation/RCU/whatisRCU.rst | 4 ++--
>
> This patch will surely need to be split up; the RCU folks, for example,
> will want to evaluate the change separately.
>
> > Documentation/core-api/kref.rst | 4 ++--
> > Documentation/core-api/list.rst | 4 ++--
> > Documentation/core-api/memory-allocation.rst | 4 ++--
> > Documentation/driver-api/mailbox.rst | 4 ++--
> > Documentation/driver-api/media/v4l2-fh.rst | 2 +-
> > Documentation/kernel-hacking/locking.rst | 4 ++--
> > Documentation/locking/locktypes.rst | 4 ++--
> > Documentation/process/coding-style.rst | 8 ++++----
> > .../sound/kernel-api/writing-an-alsa-driver.rst | 12 ++++++------
> > Documentation/spi/spi-summary.rst | 4 ++--
> > .../translations/it_IT/kernel-hacking/locking.rst | 4 ++--
> > .../translations/it_IT/locking/locktypes.rst | 4 ++--
> > .../translations/it_IT/process/coding-style.rst | 2 +-
> > .../translations/sp_SP/process/coding-style.rst | 2 +-
> > Documentation/translations/zh_CN/core-api/kref.rst | 4 ++--
> > .../translations/zh_CN/process/coding-style.rst | 2 +-
> > .../zh_CN/video4linux/v4l2-framework.txt | 2 +-
> > .../translations/zh_TW/process/coding-style.rst | 2 +-
> > 21 files changed, 42 insertions(+), 42 deletions(-)
> >
> > diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Documentation/RCU/Design/Requirements/Requirements.rst
> > index b5cdbba3ec2e..faca5a9c8c12 100644
> > --- a/Documentation/RCU/Design/Requirements/Requirements.rst
> > +++ b/Documentation/RCU/Design/Requirements/Requirements.rst
> > @@ -206,7 +206,7 @@ non-\ ``NULL``, locklessly accessing the ``->a`` and ``->b`` fields.
> >
> > 1 bool add_gp_buggy(int a, int b)
> > 2 {
> > - 3 p = kmalloc(sizeof(*p), GFP_KERNEL);
> > + 3 p = kmalloc_obj(*p, GFP_KERNEL);
>
> So you have not gone with the "implicit GFP_KERNEL" approach that Linus
> added. Given that, I assume, he wanted that to be the normal style, we
> should probably go with it.
Thank you for updating the documentation! Yes, please drop the "default"
GFP_KERNEL args in all these places. (Keep the non-GFP_KERNEL args; I
see at least GFP_ATOMIC in the docs.)
--
Kees Cook
^ permalink raw reply
* Re: [PATCH] Documentation: coding-assistants: add optional Acted-By: trailer
From: Konstantin Ryabitsev @ 2026-04-21 15:14 UTC (permalink / raw)
To: Blake Morrison
Cc: Jonathan Corbet, Shuah Khan, workflows, linux-doc, linux-kernel
In-Reply-To: <20260420142741.3187814-1-blake@truealter.com>
On Mon, Apr 20, 2026 at 02:27:46PM +0000, Blake Morrison wrote:
> The existing policy correctly separates AI tool attribution
> (Assisted-by:) from legal accountability (Signed-off-by:). In practice,
> contributors increasingly work across pseudonymous and legal-name
> contexts, and a third slot -- identifying the human sovereign identity
> under which the work was performed -- lets downstream tooling (CI,
> provenance trackers, identity systems) bind a commit to a stable handle
> without disturbing the DCO.
>
> Add Acted-By: as an optional, informational companion trailer. It does
> not replace Signed-off-by:, does not change DCO requirements, and does
> not mandate any format; the out-of-tree
> draft-morrison-identity-attributed-commits defines one such scheme, but
> contributors are free to use any handle form they prefer.
This is fairly orthogonal to what LF is already attempting to do with OpenVTC
(https://github.com/OpenVTC). I'm giving this a NACK for now, not because I'm
trying to stifle this work, but because it's going at it from the wrong angle.
The "Acted-by" trailer is clearly intended to be a field for a cryptographic
hash, not for a name/email combo.
As such, it will most likely never be accepted by the kernel community for the
same reason the community rejected the Change-ID trailer -- it's an obscure
string of characters that requires specialized tooling to parse.
Reading the IETF proposal, this is just one of the trailers proposed, as the
following are also mentioned in the draft:
1. Acted-By:
2. Executed-By:
3. Drafted-With:
4. Identity-Signature:
5. Identity-Key-Id:
6. Identity-Anchor:
I see that they need to be "optionally provided" but I can guarantee you that
a maintainer that sees a patch submission with a slew of trailers like that
will reject it (and you will get an earful from Linus).
I recommend that instead of starting by introducing a new trailer on the kernel
list, you send your overall scheme proposal to the git list instead. Some of
the claims in the draft are questionable (e.g. that tree hashes survive
rebase or cherry-pick operations), and are specifically suspect within the
context of the kernel's patch-based workflow. A tree-hash for a patch created
by the submitter will almost certainly become invalid when the maintainer runs
"git am" on their series, so the proposed scheme will never really work for
the kernel, because the vast majority of cryptographic hashes will never
validate.
So, NACK for now, and I do recommend you start on the git list instead.
-K
^ permalink raw reply
* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
From: Jani Nikula @ 2026-04-21 11:50 UTC (permalink / raw)
To: Albert Esteve, Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
In-Reply-To: <CADSE00JJq6fsYbkFN5hBD=-ZWsFG9p4_C55fp3MupMJQj0QCUQ@mail.gmail.com>
On Tue, 21 Apr 2026, Albert Esteve <aesteve@redhat.com> wrote:
> On Mon, Apr 20, 2026 at 4:47 PM Peter Zijlstra <peterz@infradead.org> wrote:
>>
>> On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
>> > From: Guenter Roeck <linux@roeck-us.net>
>> >
>> > The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
>> > intentionally trigger warning backtraces by providing bad parameters to
>> > the tested functions. What is tested is the return value, not the existence
>> > of a warning backtrace. Suppress the backtraces to avoid clogging the
>> > kernel log and distraction from real problems.
>> >
>> > Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
>> > Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
>> > Acked-by: Maíra Canal <mcanal@igalia.com>
>> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> > Cc: David Airlie <airlied@gmail.com>
>> > Cc: Daniel Vetter <daniel@ffwll.ch>
>> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
>> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
>> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
>> > ---
>> > drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
>> > 1 file changed, 14 insertions(+)
>> >
>> > diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
>> > index 17e1f34b76101..1dd7d819165e7 100644
>> > --- a/drivers/gpu/drm/tests/drm_rect_test.c
>> > +++ b/drivers/gpu/drm/tests/drm_rect_test.c
>> > @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
>> > const struct drm_rect_scale_case *params = test->param_value;
>> > int scaling_factor;
>> >
>> > + /*
>> > + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
>> > + * parameters are passed to it. This affects all unit tests with an
>> > + * error code in expected_scaling_factor.
>> > + */
>> > + KUNIT_START_SUPPRESSED_WARNING(test);
>> > scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
>> > params->min_range, params->max_range);
>> > + KUNIT_END_SUPPRESSED_WARNING(test);
>>
>> Would not something like:
>>
>> scoped_kunit_suppress() {
>> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
>> params->min_range, params->max_range);
>> }
>>
>> be better?
>
> Since KUnit already has a few macros in its API it didn't occur to me.
> Good idea, I like it. And I guess the scope approach matches well with
> your __cleanup comment in the first patch. If no one opposes, I will
> work toward that pattern for the next version.
There's a catch with kunit and __cleanup and thus (scoped) guards. Kunit
runs in ktreads, asserts lead to kthread_exit() and the __cleanup won't
be called.
Warning suppression being part of kunit infrastructure, asserts can and
should end the suppression too. But setting the example (scoped) guards
are safe in kunit tests in general feels like a trap waiting to happen.
BR,
Jani.
>
>>
>> Also, how can you stand all this screaming in the code?
>>
>
> Again, KUnit already contains many macros, so this use didn't register
> as such. Now I will not be able to unsee it.
>
>
--
Jani Nikula, Intel
^ permalink raw reply
* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
From: Albert Esteve @ 2026-04-21 8:49 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
In-Reply-To: <20260420144702.GM3102624@noisy.programming.kicks-ass.net>
On Mon, Apr 20, 2026 at 4:47 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
> > From: Guenter Roeck <linux@roeck-us.net>
> >
> > The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
> > intentionally trigger warning backtraces by providing bad parameters to
> > the tested functions. What is tested is the return value, not the existence
> > of a warning backtrace. Suppress the backtraces to avoid clogging the
> > kernel log and distraction from real problems.
> >
> > Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> > Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> > Acked-by: Maíra Canal <mcanal@igalia.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: David Airlie <airlied@gmail.com>
> > Cc: Daniel Vetter <daniel@ffwll.ch>
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
> > drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
> > index 17e1f34b76101..1dd7d819165e7 100644
> > --- a/drivers/gpu/drm/tests/drm_rect_test.c
> > +++ b/drivers/gpu/drm/tests/drm_rect_test.c
> > @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
> > const struct drm_rect_scale_case *params = test->param_value;
> > int scaling_factor;
> >
> > + /*
> > + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
> > + * parameters are passed to it. This affects all unit tests with an
> > + * error code in expected_scaling_factor.
> > + */
> > + KUNIT_START_SUPPRESSED_WARNING(test);
> > scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> > params->min_range, params->max_range);
> > + KUNIT_END_SUPPRESSED_WARNING(test);
>
> Would not something like:
>
> scoped_kunit_suppress() {
> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> params->min_range, params->max_range);
> }
>
> be better?
Since KUnit already has a few macros in its API it didn't occur to me.
Good idea, I like it. And I guess the scope approach matches well with
your __cleanup comment in the first patch. If no one opposes, I will
work toward that pattern for the next version.
>
> Also, how can you stand all this screaming in the code?
>
Again, KUnit already contains many macros, so this use didn't register
as such. Now I will not be able to unsee it.
^ permalink raw reply
* Re: [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
From: Albert Esteve @ 2026-04-21 8:41 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati
In-Reply-To: <20260420144453.GK3102624@noisy.programming.kicks-ass.net>
On Mon, Apr 20, 2026 at 4:45 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:04PM +0200, Albert Esteve wrote:
> > From: Alessandro Carminati <acarmina@redhat.com>
> >
> > KUnit support is not consistently present across distributions, some
> > include it in their stock kernels, while others do not.
> > While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
> > features, the fact that some distros ship with KUnit enabled means it's
> > important to minimize the runtime impact of this patch.
> >
> > To that end, this patch adds an atomic counter that tracks the number
> > of active suppressions. __kunit_is_suppressed_warning() checks this
> > counter first and returns immediately when no suppressions are active,
> > avoiding RCU-protected list traversal in the common case.
> >
> > Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> > Signed-off-by: Albert Esteve <aesteve@redhat.com>
> > ---
> > lib/kunit/bug.c | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> > index 356c8a5928828..a7a88f0670d44 100644
> > --- a/lib/kunit/bug.c
> > +++ b/lib/kunit/bug.c
> > @@ -8,6 +8,7 @@
> >
> > #include <kunit/bug.h>
> > #include <kunit/resource.h>
> > +#include <linux/atomic.h>
> > #include <linux/export.h>
> > #include <linux/rculist.h>
> > #include <linux/sched.h>
> > @@ -15,11 +16,13 @@
> > #ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> >
> > static LIST_HEAD(suppressed_warnings);
> > +static atomic_t suppressed_warnings_cnt = ATOMIC_INIT(0);
> >
> > static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> > {
> > list_del_rcu(&warning->node);
> > synchronize_rcu(); /* Wait for readers to finish */
> > + atomic_dec(&suppressed_warnings_cnt);
> > }
> >
> > KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> > @@ -37,6 +40,7 @@ __kunit_start_suppress_warning(struct kunit *test)
> > return NULL;
> >
> > warning->task = current;
> > + atomic_inc(&suppressed_warnings_cnt);
> > list_add_rcu(&warning->node, &suppressed_warnings);
> >
> > ret = kunit_add_action_or_reset(test,
> > @@ -68,6 +72,9 @@ bool __kunit_is_suppressed_warning(void)
> > {
> > struct __suppressed_warning *warning;
> >
> > + if (!atomic_read(&suppressed_warnings_cnt))
> > + return false;
> > +
> > rcu_read_lock();
> > list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> > if (warning->task == current) {
> >
>
> So the thing you're skipping is:
>
> rcu_read_lock();
> list_for_each_entry_rcu() {
> }
> rcu_read_unlock();
>
> Which is really cheap. Did you actually have performance numbers for
> this?
No, I do not have performance numbers. I kept the counter and the
separate patch for consistency with the previous version of the
series. But you have a good point, the skipped part is really cheap.
>
> A possibly better option is to add a static_branch() that could elide
> any and all memory access.
>
Previous version had static_branch and I removed it because I
understood from the discussion that the gains would not be significant
as performance gains are irrelevant in warn slowpath. But I think it
would make sense for a disabled feature. I will rework this for the
next version, remove the counter and use static_branch as suggested.
^ permalink raw reply
* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
From: Albert Esteve @ 2026-04-21 8:29 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
In-Reply-To: <20260420144512.GL3102624@noisy.programming.kicks-ass.net>
On Mon, Apr 20, 2026 at 4:45 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> > +bool __kunit_is_suppressed_warning(void)
> > +{
> > + struct __suppressed_warning *warning;
> > +
> > + rcu_read_lock();
>
> guard(rcu)();
Nice. I saw plenty of examples using explicit calls, but I had missed
the guard. Thanks for pointing it out.
>
> > + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> > + if (warning->task == current) {
> > + warning->counter++;
> > + rcu_read_unlock();
> > + return true;
> > + }
> > + }
> > + rcu_read_unlock();
> > +
> > + return false;
> > +}
> > +
> > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> >
> > --
> > 2.52.0
> >
>
^ permalink raw reply
* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
From: Albert Esteve @ 2026-04-21 8:22 UTC (permalink / raw)
To: Peter Zijlstra
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
In-Reply-To: <20260420143951.GJ3102624@noisy.programming.kicks-ass.net>
On Mon, Apr 20, 2026 at 4:40 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> > From: Alessandro Carminati <acarmina@redhat.com>
> >
> > Some unit tests intentionally trigger warning backtraces by passing bad
> > parameters to kernel API functions. Such unit tests typically check the
> > return value from such calls, not the existence of the warning backtrace.
> >
> > Such intentionally generated warning backtraces are neither desirable
> > nor useful for a number of reasons:
> > - They can result in overlooked real problems.
> > - A warning that suddenly starts to show up in unit tests needs to be
> > investigated and has to be marked to be ignored, for example by
> > adjusting filter scripts. Such filters are ad hoc because there is
> > no real standard format for warnings. On top of that, such filter
> > scripts would require constant maintenance.
> >
> > Solve the problem by providing a means to identify and suppress specific
> > warning backtraces while executing test code. Support suppressing multiple
> > backtraces while at the same time limiting changes to generic code to the
> > absolute minimum.
> >
> > Implementation details:
> > Suppression is checked at two points in the warning path:
> > - In warn_slowpath_fmt(), the check runs before any output, fully
> > suppressing both message and backtrace.
> > - In __report_bug(), the check runs before __warn() is called,
> > suppressing the backtrace and stack dump. Note that on this path,
> > the WARN() format message may still appear in the kernel log since
> > __warn_printk() runs before the trap that enters __report_bug().
>
> This is for architectures that implement __WARN_FLAGS but not
> __WARN_printf right? (which is arm64, loongarch, parisc, powerpc, riscv,
> sh, afaict). ARM64 should eventually get __WARN_printf, but other than
> that this should be fixable by moving __WARN_FLAGS() into
> __warn_printk() or so. This is the only __warn_printk() user anyway.
Right. On that path, __warn_printk() prints the message before
__WARN_FLAGS() triggers the trap into __report_bug(), so the
suppression check in __report_bug() only catches the backtrace.
Adding the suppression check to __warn_printk() as well should close
this gap, since it's the only caller in the generic __WARN_printf
path. Something like:
```
diff --git a/kernel/panic.c b/kernel/panic.c
index d7a7a679f56c4..cd73038b7c0bd 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -1108,9 +1108,14 @@ EXPORT_SYMBOL(warn_slowpath_fmt);
#else
void __warn_printk(const char *fmt, ...)
{
- bool rcu = warn_rcu_enter();
+ bool rcu;
va_list args;
+ if (__kunit_is_suppressed_warning())
+ return;
+
+ rcu = warn_rcu_enter();
+
pr_warn(CUT_HERE);
va_start(args, fmt);
```
Note that the suppression counter tracking may need a small adjustment
to avoid double-counting, since __report_bug() will still see the same
warning through the trap path, but the approach itself should be
straightforward.
>
>
> > diff --git a/include/kunit/bug.h b/include/kunit/bug.h
> > new file mode 100644
> > index 0000000000000..e52c9d21d9fe6
> > --- /dev/null
> > +++ b/include/kunit/bug.h
> > @@ -0,0 +1,56 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * KUnit helpers for backtrace suppression
> > + *
> > + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> > + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> > + */
> > +
> > +#ifndef _KUNIT_BUG_H
> > +#define _KUNIT_BUG_H
> > +
> > +#ifndef __ASSEMBLY__
> > +
> > +#include <linux/kconfig.h>
> > +
> > +struct kunit;
> > +
> > +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> > +
> > +#include <linux/types.h>
> > +
> > +struct task_struct;
> > +
> > +struct __suppressed_warning {
> > + struct list_head node;
> > + struct task_struct *task;
> > + int counter;
> > +};
> > +
> > +struct __suppressed_warning *
> > +__kunit_start_suppress_warning(struct kunit *test);
> > +void __kunit_end_suppress_warning(struct kunit *test,
> > + struct __suppressed_warning *warning);
> > +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
> > +bool __kunit_is_suppressed_warning(void);
> > +
> > +#define KUNIT_START_SUPPRESSED_WARNING(test) \
> > + struct __suppressed_warning *__kunit_suppress = \
> > + __kunit_start_suppress_warning(test)
> > +
> > +#define KUNIT_END_SUPPRESSED_WARNING(test) \
> > + __kunit_end_suppress_warning(test, __kunit_suppress)
>
> We have __cleanup for this?
I was unfamiliar with this attribute. I have looked into it a bit, and
it could be a good fit. I saw a good example in seqlock. I could try
to use it for the next version.
>
> > +
> > +#define KUNIT_SUPPRESSED_WARNING_COUNT() \
> > + __kunit_suppressed_warning_count(__kunit_suppress)
> > +
> > +#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> > +
> > +#define KUNIT_START_SUPPRESSED_WARNING(test)
> > +#define KUNIT_END_SUPPRESSED_WARNING(test)
> > +#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
> > +static inline bool __kunit_is_suppressed_warning(void) { return false; }
> > +
> > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> > +#endif /* __ASSEMBLY__ */
> > +#endif /* _KUNIT_BUG_H */
>
> > diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> > index 656f1fa35abcc..fe177ff3ebdef 100644
> > --- a/lib/kunit/Makefile
> > +++ b/lib/kunit/Makefile
> > @@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
> > kunit-objs += debugfs.o
> > endif
> >
> > -# KUnit 'hooks' are built-in even when KUnit is built as a module.
> > -obj-$(if $(CONFIG_KUNIT),y) += hooks.o
> > +# KUnit 'hooks' and bug handling are built-in even when KUnit is built
> > +# as a module.
> > +obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
> > + bug.o
> >
> > obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
> > obj-$(CONFIG_KUNIT_TEST) += platform-test.o
> > diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> > new file mode 100644
> > index 0000000000000..356c8a5928828
> > --- /dev/null
> > +++ b/lib/kunit/bug.c
> > @@ -0,0 +1,84 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * KUnit helpers for backtrace suppression
> > + *
> > + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> > + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> > + */
> > +
> > +#include <kunit/bug.h>
> > +#include <kunit/resource.h>
> > +#include <linux/export.h>
> > +#include <linux/rculist.h>
> > +#include <linux/sched.h>
> > +
> > +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> > +
> > +static LIST_HEAD(suppressed_warnings);
> > +
> > +static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> > +{
> > + list_del_rcu(&warning->node);
> > + synchronize_rcu(); /* Wait for readers to finish */
> > +}
> > +
> > +KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> > + __kunit_suppress_warning_remove,
> > + struct __suppressed_warning *);
> > +
> > +struct __suppressed_warning *
> > +__kunit_start_suppress_warning(struct kunit *test)
> > +{
> > + struct __suppressed_warning *warning;
> > + int ret;
> > +
> > + warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
> > + if (!warning)
> > + return NULL;
> > +
> > + warning->task = current;
> > + list_add_rcu(&warning->node, &suppressed_warnings);
>
> What if anything serializes this global list?
I considered adding a spinlock, but since the KUnit executor runs
tests sequentially and it had not been a concern in previous versions,
I left it out to keep the changeset minimal unless someone complains.
If we want a hard guarantee, I'm happy to add the spinlock for the
next version.
>
> > +
> > + ret = kunit_add_action_or_reset(test,
> > + __kunit_suppress_warning_cleanup,
> > + warning);
> > + if (ret)
> > + return NULL;
> > +
> > + return warning;
> > +}
> > +EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
> > +
> > +void __kunit_end_suppress_warning(struct kunit *test,
> > + struct __suppressed_warning *warning)
> > +{
> > + if (!warning)
> > + return;
> > + kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
> > +}
> > +EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
> > +
> > +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
> > +{
> > + return warning ? warning->counter : 0;
> > +}
> > +EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
> > +
> > +bool __kunit_is_suppressed_warning(void)
> > +{
> > + struct __suppressed_warning *warning;
> > +
> > + rcu_read_lock();
> > + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> > + if (warning->task == current) {
> > + warning->counter++;
> > + rcu_read_unlock();
> > + return true;
> > + }
> > + }
> > + rcu_read_unlock();
> > +
> > + return false;
> > +}
> > +
> > +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> >
> > --
> > 2.52.0
> >
>
^ permalink raw reply related
* Re: [PATCH] Documentation: coding-assistants: add optional Acted-By: trailer
From: Vlastimil Babka @ 2026-04-21 7:57 UTC (permalink / raw)
To: Blake, Greg KH
Cc: Jonathan Corbet, Shuah Khan, workflows, linux-doc, linux-kernel
In-Reply-To: <IF6AC3bPCYsGyyxsgSQlwZXnA3BJJh61OW6a3KznzbsmDPG4DtricBAzsxyOjDQZ-RHBEkgsjRdaVKQ6i8gqv1bd2AGwC0BTJwBErNHOqx4=@truealter.com>
On 4/21/26 03:04, Blake wrote:
> On Tuesday, 21 April 2026 at 3:40 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
>> I really do not understand, how would this actually be used?
>> And as you have to have a signed-off-by, why would you use two
>> different names for yourself this way?
>
> Signed-off-by and Acted-By answer different questions. Signed-off-by
> requires a real name for DCO attestation.
AFAIU that's an outdated claim. See:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d4563201f33a022fc0353033d9dfeb1606a88330
^ permalink raw reply
* Re: [PATCH] Documentation: coding-assistants: add optional Acted-By: trailer
From: Blake @ 2026-04-21 1:04 UTC (permalink / raw)
To: Greg KH; +Cc: Jonathan Corbet, Shuah Khan, workflows, linux-doc, linux-kernel
In-Reply-To: <2026042035-retention-platonic-e5d5@gregkh>
On Tuesday, 21 April 2026 at 3:40 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> I really do not understand, how would this actually be used?
Git history uses email addresses as the de-facto identity key and
email addresses aren't stable across a lifetime or a career and,
increasingly, aren't meaningful even within a single commit.
Contributors move between employers and domains over time; companies
rename and migrate their workforce onto new domains; and plenty of
commits land with From: lines like blake@desktop or
root@localhost.localdomain because git's username@hostname fallback
fired before user.email was set.
.mailmap partially fixes the first case inside a single tree but
doesn't travel across repositories and can't synthesise an identity
where the From: never carried one. A declared Acted-By trailer gives
the human a stable key that survives employer changes, domain
migrations, misconfigured clients, and cross-tree lookups.
> And as you have to have a signed-off-by, why would you use two
> different names for yourself this way?
Signed-off-by and Acted-By answer different questions. Signed-off-by
requires a real name for DCO attestation. Acted-By names the stable
working identity the same human operates under across contexts —
which for most contributors on a stable setup collapses to the same
name, and the trailer adds nothing. They diverge when:
- the same human contributes under different employer emails over
a long career;
- an employer renames and migrates its workforce to a new domain;
- a contributor publishes under a stable pseudonym but their DCO
Signed-off-by has to carry their legal name;
- the From: line is machine-generated noise (blake@desktop,
user@hostname) and carries no identity information at all.
> And who is asking for this? Who would want to use it? How would
> you use it for this very commit?
For this very commit I wouldn't need it as Signed-off-by is
sufficient. The patch defines a slot in the docs; the commits that
benefit from the slot are other commits in other trees where the
divergence cases above bite. Pseudonymous contributors and
long-career maintainers whose email addresses have changed are the
current constituency; anyone writing provenance or review-routing
tooling that today falls back on email-fuzzing is the other.
If the sense is that optional trailers with narrow audiences don't
earn a footnote in coding-assistants.rst, I'm happy to withdraw and
keep this out-of-tree.
thanks,
Blake
^ permalink raw reply
* Re: [PATCH] Documentation: coding-assistants: add optional Acted-By: trailer
From: Greg KH @ 2026-04-20 17:40 UTC (permalink / raw)
To: Blake Morrison
Cc: Jonathan Corbet, Shuah Khan, workflows, linux-doc, linux-kernel
In-Reply-To: <20260420142741.3187814-1-blake@truealter.com>
On Mon, Apr 20, 2026 at 02:27:46PM +0000, Blake Morrison wrote:
> The existing policy correctly separates AI tool attribution
> (Assisted-by:) from legal accountability (Signed-off-by:). In practice,
> contributors increasingly work across pseudonymous and legal-name
> contexts, and a third slot -- identifying the human sovereign identity
> under which the work was performed -- lets downstream tooling (CI,
> provenance trackers, identity systems) bind a commit to a stable handle
> without disturbing the DCO.
>
> Add Acted-By: as an optional, informational companion trailer. It does
> not replace Signed-off-by:, does not change DCO requirements, and does
> not mandate any format; the out-of-tree
> draft-morrison-identity-attributed-commits defines one such scheme, but
> contributors are free to use any handle form they prefer.
>
> The three trailers then map cleanly:
>
> * Assisted-by: -- what tool drafted this
> * Acted-By: -- who the human was, as a handle
I really do not understand, how would this actually be used?
And as you have to have a signed-off-by, why would you use two different
names for yourself this way?
And who is asking for this? Who would want to use it? How would you
use it for this very commit?
confused,
greg k-h
^ permalink raw reply
* Re: [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
From: Peter Zijlstra @ 2026-04-20 14:47 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Simona Vetter
In-Reply-To: <20260420-kunit_add_support-v7-4-e8bc6e0f70de@redhat.com>
On Mon, Apr 20, 2026 at 02:28:06PM +0200, Albert Esteve wrote:
> From: Guenter Roeck <linux@roeck-us.net>
>
> The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
> intentionally trigger warning backtraces by providing bad parameters to
> the tested functions. What is tested is the return value, not the existence
> of a warning backtrace. Suppress the backtraces to avoid clogging the
> kernel log and distraction from real problems.
>
> Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
> Acked-by: Maíra Canal <mcanal@igalia.com>
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
> drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
> index 17e1f34b76101..1dd7d819165e7 100644
> --- a/drivers/gpu/drm/tests/drm_rect_test.c
> +++ b/drivers/gpu/drm/tests/drm_rect_test.c
> @@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
> const struct drm_rect_scale_case *params = test->param_value;
> int scaling_factor;
>
> + /*
> + * drm_rect_calc_hscale() generates a warning backtrace whenever bad
> + * parameters are passed to it. This affects all unit tests with an
> + * error code in expected_scaling_factor.
> + */
> + KUNIT_START_SUPPRESSED_WARNING(test);
> scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
> params->min_range, params->max_range);
> + KUNIT_END_SUPPRESSED_WARNING(test);
Would not something like:
scoped_kunit_suppress() {
scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
params->min_range, params->max_range);
}
be better?
Also, how can you stand all this screaming in the code?
^ permalink raw reply
* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
From: Peter Zijlstra @ 2026-04-20 14:45 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
In-Reply-To: <20260420-kunit_add_support-v7-1-e8bc6e0f70de@redhat.com>
On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> +bool __kunit_is_suppressed_warning(void)
> +{
> + struct __suppressed_warning *warning;
> +
> + rcu_read_lock();
guard(rcu)();
> + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> + if (warning->task == current) {
> + warning->counter++;
> + rcu_read_unlock();
> + return true;
> + }
> + }
> + rcu_read_unlock();
> +
> + return false;
> +}
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
>
> --
> 2.52.0
>
^ permalink raw reply
* Re: [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
From: Peter Zijlstra @ 2026-04-20 14:44 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati
In-Reply-To: <20260420-kunit_add_support-v7-2-e8bc6e0f70de@redhat.com>
On Mon, Apr 20, 2026 at 02:28:04PM +0200, Albert Esteve wrote:
> From: Alessandro Carminati <acarmina@redhat.com>
>
> KUnit support is not consistently present across distributions, some
> include it in their stock kernels, while others do not.
> While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
> features, the fact that some distros ship with KUnit enabled means it's
> important to minimize the runtime impact of this patch.
>
> To that end, this patch adds an atomic counter that tracks the number
> of active suppressions. __kunit_is_suppressed_warning() checks this
> counter first and returns immediately when no suppressions are active,
> avoiding RCU-protected list traversal in the common case.
>
> Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
> Signed-off-by: Albert Esteve <aesteve@redhat.com>
> ---
> lib/kunit/bug.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> index 356c8a5928828..a7a88f0670d44 100644
> --- a/lib/kunit/bug.c
> +++ b/lib/kunit/bug.c
> @@ -8,6 +8,7 @@
>
> #include <kunit/bug.h>
> #include <kunit/resource.h>
> +#include <linux/atomic.h>
> #include <linux/export.h>
> #include <linux/rculist.h>
> #include <linux/sched.h>
> @@ -15,11 +16,13 @@
> #ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
>
> static LIST_HEAD(suppressed_warnings);
> +static atomic_t suppressed_warnings_cnt = ATOMIC_INIT(0);
>
> static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> {
> list_del_rcu(&warning->node);
> synchronize_rcu(); /* Wait for readers to finish */
> + atomic_dec(&suppressed_warnings_cnt);
> }
>
> KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> @@ -37,6 +40,7 @@ __kunit_start_suppress_warning(struct kunit *test)
> return NULL;
>
> warning->task = current;
> + atomic_inc(&suppressed_warnings_cnt);
> list_add_rcu(&warning->node, &suppressed_warnings);
>
> ret = kunit_add_action_or_reset(test,
> @@ -68,6 +72,9 @@ bool __kunit_is_suppressed_warning(void)
> {
> struct __suppressed_warning *warning;
>
> + if (!atomic_read(&suppressed_warnings_cnt))
> + return false;
> +
> rcu_read_lock();
> list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> if (warning->task == current) {
>
So the thing you're skipping is:
rcu_read_lock();
list_for_each_entry_rcu() {
}
rcu_read_unlock();
Which is really cheap. Did you actually have performance numbers for
this?
A possibly better option is to add a static_branch() that could elide
any and all memory access.
^ permalink raw reply
* Re: [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
From: Peter Zijlstra @ 2026-04-20 14:39 UTC (permalink / raw)
To: Albert Esteve
Cc: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton,
linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, Alessandro Carminati, Guenter Roeck,
Kees Cook
In-Reply-To: <20260420-kunit_add_support-v7-1-e8bc6e0f70de@redhat.com>
On Mon, Apr 20, 2026 at 02:28:03PM +0200, Albert Esteve wrote:
> From: Alessandro Carminati <acarmina@redhat.com>
>
> Some unit tests intentionally trigger warning backtraces by passing bad
> parameters to kernel API functions. Such unit tests typically check the
> return value from such calls, not the existence of the warning backtrace.
>
> Such intentionally generated warning backtraces are neither desirable
> nor useful for a number of reasons:
> - They can result in overlooked real problems.
> - A warning that suddenly starts to show up in unit tests needs to be
> investigated and has to be marked to be ignored, for example by
> adjusting filter scripts. Such filters are ad hoc because there is
> no real standard format for warnings. On top of that, such filter
> scripts would require constant maintenance.
>
> Solve the problem by providing a means to identify and suppress specific
> warning backtraces while executing test code. Support suppressing multiple
> backtraces while at the same time limiting changes to generic code to the
> absolute minimum.
>
> Implementation details:
> Suppression is checked at two points in the warning path:
> - In warn_slowpath_fmt(), the check runs before any output, fully
> suppressing both message and backtrace.
> - In __report_bug(), the check runs before __warn() is called,
> suppressing the backtrace and stack dump. Note that on this path,
> the WARN() format message may still appear in the kernel log since
> __warn_printk() runs before the trap that enters __report_bug().
This is for architectures that implement __WARN_FLAGS but not
__WARN_printf right? (which is arm64, loongarch, parisc, powerpc, riscv,
sh, afaict). ARM64 should eventually get __WARN_printf, but other than
that this should be fixable by moving __WARN_FLAGS() into
__warn_printk() or so. This is the only __warn_printk() user anyway.
> diff --git a/include/kunit/bug.h b/include/kunit/bug.h
> new file mode 100644
> index 0000000000000..e52c9d21d9fe6
> --- /dev/null
> +++ b/include/kunit/bug.h
> @@ -0,0 +1,56 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * KUnit helpers for backtrace suppression
> + *
> + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#ifndef _KUNIT_BUG_H
> +#define _KUNIT_BUG_H
> +
> +#ifndef __ASSEMBLY__
> +
> +#include <linux/kconfig.h>
> +
> +struct kunit;
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +
> +#include <linux/types.h>
> +
> +struct task_struct;
> +
> +struct __suppressed_warning {
> + struct list_head node;
> + struct task_struct *task;
> + int counter;
> +};
> +
> +struct __suppressed_warning *
> +__kunit_start_suppress_warning(struct kunit *test);
> +void __kunit_end_suppress_warning(struct kunit *test,
> + struct __suppressed_warning *warning);
> +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
> +bool __kunit_is_suppressed_warning(void);
> +
> +#define KUNIT_START_SUPPRESSED_WARNING(test) \
> + struct __suppressed_warning *__kunit_suppress = \
> + __kunit_start_suppress_warning(test)
> +
> +#define KUNIT_END_SUPPRESSED_WARNING(test) \
> + __kunit_end_suppress_warning(test, __kunit_suppress)
We have __cleanup for this?
> +
> +#define KUNIT_SUPPRESSED_WARNING_COUNT() \
> + __kunit_suppressed_warning_count(__kunit_suppress)
> +
> +#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +
> +#define KUNIT_START_SUPPRESSED_WARNING(test)
> +#define KUNIT_END_SUPPRESSED_WARNING(test)
> +#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
> +static inline bool __kunit_is_suppressed_warning(void) { return false; }
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
> +#endif /* __ASSEMBLY__ */
> +#endif /* _KUNIT_BUG_H */
> diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
> index 656f1fa35abcc..fe177ff3ebdef 100644
> --- a/lib/kunit/Makefile
> +++ b/lib/kunit/Makefile
> @@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
> kunit-objs += debugfs.o
> endif
>
> -# KUnit 'hooks' are built-in even when KUnit is built as a module.
> -obj-$(if $(CONFIG_KUNIT),y) += hooks.o
> +# KUnit 'hooks' and bug handling are built-in even when KUnit is built
> +# as a module.
> +obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
> + bug.o
>
> obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
> obj-$(CONFIG_KUNIT_TEST) += platform-test.o
> diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
> new file mode 100644
> index 0000000000000..356c8a5928828
> --- /dev/null
> +++ b/lib/kunit/bug.c
> @@ -0,0 +1,84 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * KUnit helpers for backtrace suppression
> + *
> + * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
> + * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
> + */
> +
> +#include <kunit/bug.h>
> +#include <kunit/resource.h>
> +#include <linux/export.h>
> +#include <linux/rculist.h>
> +#include <linux/sched.h>
> +
> +#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
> +
> +static LIST_HEAD(suppressed_warnings);
> +
> +static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
> +{
> + list_del_rcu(&warning->node);
> + synchronize_rcu(); /* Wait for readers to finish */
> +}
> +
> +KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
> + __kunit_suppress_warning_remove,
> + struct __suppressed_warning *);
> +
> +struct __suppressed_warning *
> +__kunit_start_suppress_warning(struct kunit *test)
> +{
> + struct __suppressed_warning *warning;
> + int ret;
> +
> + warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
> + if (!warning)
> + return NULL;
> +
> + warning->task = current;
> + list_add_rcu(&warning->node, &suppressed_warnings);
What if anything serializes this global list?
> +
> + ret = kunit_add_action_or_reset(test,
> + __kunit_suppress_warning_cleanup,
> + warning);
> + if (ret)
> + return NULL;
> +
> + return warning;
> +}
> +EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
> +
> +void __kunit_end_suppress_warning(struct kunit *test,
> + struct __suppressed_warning *warning)
> +{
> + if (!warning)
> + return;
> + kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
> +}
> +EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
> +
> +int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
> +{
> + return warning ? warning->counter : 0;
> +}
> +EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
> +
> +bool __kunit_is_suppressed_warning(void)
> +{
> + struct __suppressed_warning *warning;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
> + if (warning->task == current) {
> + warning->counter++;
> + rcu_read_unlock();
> + return true;
> + }
> + }
> + rcu_read_unlock();
> +
> + return false;
> +}
> +
> +#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
>
> --
> 2.52.0
>
^ permalink raw reply
* [PATCH] Documentation: coding-assistants: add optional Acted-By: trailer
From: Blake Morrison @ 2026-04-20 14:27 UTC (permalink / raw)
To: Jonathan Corbet, Shuah Khan
Cc: workflows, linux-doc, linux-kernel, Blake Morrison
The existing policy correctly separates AI tool attribution
(Assisted-by:) from legal accountability (Signed-off-by:). In practice,
contributors increasingly work across pseudonymous and legal-name
contexts, and a third slot -- identifying the human sovereign identity
under which the work was performed -- lets downstream tooling (CI,
provenance trackers, identity systems) bind a commit to a stable handle
without disturbing the DCO.
Add Acted-By: as an optional, informational companion trailer. It does
not replace Signed-off-by:, does not change DCO requirements, and does
not mandate any format; the out-of-tree
draft-morrison-identity-attributed-commits defines one such scheme, but
contributors are free to use any handle form they prefer.
The three trailers then map cleanly:
* Assisted-by: -- what tool drafted this
* Acted-By: -- who the human was, as a handle
* Signed-off-by: -- legal DCO attestation
This mirrors the informal separation already present in commits that
carry both a pseudonymous Reported-by: and a separate Signed-off-by:.
Signed-off-by: Blake Morrison <blake@truealter.com>
---
Documentation/process/coding-assistants.rst | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/Documentation/process/coding-assistants.rst b/Documentation/process/coding-assistants.rst
index 899f4459c..b1d2d2f66 100644
--- a/Documentation/process/coding-assistants.rst
+++ b/Documentation/process/coding-assistants.rst
@@ -57,3 +57,16 @@ Basic development tools (git, gcc, make, editors) should not be listed.
Example::
Assisted-by: Claude:claude-3-opus coccinelle sparse
+
+Contributors may optionally add an ``Acted-By:`` tag identifying the
+human sovereign identity under which the work was performed, in a form
+stable across pseudonymous and legal-name contexts::
+
+ Acted-By: handle
+
+``Acted-By:`` is informational. It does not replace ``Signed-off-by:``;
+DCO attestation remains mandatory. Where ``Assisted-by:`` identifies
+*what tooling* contributed, ``Acted-By:`` identifies *who* the human
+was, as a stable handle. Handle format is out of scope for this
+document; draft-morrison-identity-attributed-commits in the IETF
+document stream describes one such scheme.
--
2.53.0
^ permalink raw reply related
* Re: [PATCH] docs: maintainer-netdev: fix typo in "targeting"
From: Breno Leitao @ 2026-04-20 13:35 UTC (permalink / raw)
To: Ariful Islam Shoikot; +Cc: netdev, linux-doc, workflows, linux-kernel
In-Reply-To: <20260420114554.1026-1-islamarifulshoikat@gmail.com>
On Mon, Apr 20, 2026 at 05:45:53PM +0600, Ariful Islam Shoikot wrote:
> Fix spelling mistake "targgeting" -> "targeting" in
> maintainer-netdev.rst
>
> No functional change.
>
> Signed-off-by: Ariful Islam Shoikot <islamarifulshoikat@gmail.com>
Reviewed-by: Breno Leitao <leitao@debian.org>
^ permalink raw reply
* [PATCH v7 5/5] kunit: Add documentation for warning backtrace suppression API
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter,
Alessandro Carminati, Albert Esteve, Kees Cook, David Gow
In-Reply-To: <20260420-kunit_add_support-v7-0-e8bc6e0f70de@redhat.com>
From: Guenter Roeck <linux@roeck-us.net>
Document API functions for suppressing warning backtraces.
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
Documentation/dev-tools/kunit/usage.rst | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
diff --git a/Documentation/dev-tools/kunit/usage.rst b/Documentation/dev-tools/kunit/usage.rst
index ebd06f5ea4550..76e85412f240e 100644
--- a/Documentation/dev-tools/kunit/usage.rst
+++ b/Documentation/dev-tools/kunit/usage.rst
@@ -157,6 +157,34 @@ Alternatively, one can take full control over the error message by using
if (some_setup_function())
KUNIT_FAIL(test, "Failed to setup thing for testing");
+Suppressing warning backtraces
+------------------------------
+
+Some unit tests trigger warning backtraces either intentionally or as side
+effect. Such backtraces are normally undesirable since they distract from
+the actual test and may result in the impression that there is a problem.
+
+Such backtraces can be suppressed with **task scope suppression**: while
+``START`` / ``END`` is active on the current task, the backtrace and stack
+dump from warnings on that task are suppressed. Wrap the call from your test
+in that window, like shown in the following code.
+
+.. code-block:: c
+
+ static void some_test(struct kunit *test)
+ {
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ trigger_backtrace();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+ }
+
+``KUNIT_SUPPRESSED_WARNING_COUNT()`` returns the number of suppressed backtraces.
+If the suppressed backtrace was triggered on purpose, this can be used to check
+if the backtrace was actually triggered.
+
+.. code-block:: c
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
Test Suites
~~~~~~~~~~~
@@ -1211,4 +1239,4 @@ For example:
dev_managed_string = devm_kstrdup(fake_device, "Hello, World!");
// Everything is cleaned up automatically when the test ends.
- }
\ No newline at end of file
+ }
--
2.52.0
^ permalink raw reply related
* [PATCH v7 4/5] drm: Suppress intentional warning backtraces in scaling unit tests
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter, Maíra Canal,
Alessandro Carminati, Albert Esteve, Simona Vetter
In-Reply-To: <20260420-kunit_add_support-v7-0-e8bc6e0f70de@redhat.com>
From: Guenter Roeck <linux@roeck-us.net>
The drm_test_rect_calc_hscale and drm_test_rect_calc_vscale unit tests
intentionally trigger warning backtraces by providing bad parameters to
the tested functions. What is tested is the return value, not the existence
of a warning backtrace. Suppress the backtraces to avoid clogging the
kernel log and distraction from real problems.
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Maíra Canal <mcanal@igalia.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
drivers/gpu/drm/tests/drm_rect_test.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/gpu/drm/tests/drm_rect_test.c b/drivers/gpu/drm/tests/drm_rect_test.c
index 17e1f34b76101..1dd7d819165e7 100644
--- a/drivers/gpu/drm/tests/drm_rect_test.c
+++ b/drivers/gpu/drm/tests/drm_rect_test.c
@@ -409,8 +409,15 @@ static void drm_test_rect_calc_hscale(struct kunit *test)
const struct drm_rect_scale_case *params = test->param_value;
int scaling_factor;
+ /*
+ * drm_rect_calc_hscale() generates a warning backtrace whenever bad
+ * parameters are passed to it. This affects all unit tests with an
+ * error code in expected_scaling_factor.
+ */
+ KUNIT_START_SUPPRESSED_WARNING(test);
scaling_factor = drm_rect_calc_hscale(¶ms->src, ¶ms->dst,
params->min_range, params->max_range);
+ KUNIT_END_SUPPRESSED_WARNING(test);
KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
}
@@ -420,8 +427,15 @@ static void drm_test_rect_calc_vscale(struct kunit *test)
const struct drm_rect_scale_case *params = test->param_value;
int scaling_factor;
+ /*
+ * drm_rect_calc_vscale() generates a warning backtrace whenever bad
+ * parameters are passed to it. This affects all unit tests with an
+ * error code in expected_scaling_factor.
+ */
+ KUNIT_START_SUPPRESSED_WARNING(test);
scaling_factor = drm_rect_calc_vscale(¶ms->src, ¶ms->dst,
params->min_range, params->max_range);
+ KUNIT_END_SUPPRESSED_WARNING(test);
KUNIT_EXPECT_EQ(test, scaling_factor, params->expected_scaling_factor);
}
--
2.52.0
^ permalink raw reply related
* [PATCH v7 3/5] kunit: Add backtrace suppression self-tests
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Guenter Roeck,
Linux Kernel Functional Testing, Dan Carpenter,
Alessandro Carminati, Albert Esteve, Kees Cook
In-Reply-To: <20260420-kunit_add_support-v7-0-e8bc6e0f70de@redhat.com>
From: Guenter Roeck <linux@roeck-us.net>
Add unit tests to verify that warning backtrace suppression works,
covering WARN() and WARN_ON() with direct calls, indirect calls
through helper functions, and multiple warnings in a single window.
If backtrace suppression does _not_ work, the unit tests will likely
trigger unsuppressed backtraces, which should actually help to get
the affected architectures / platforms fixed.
Tested-by: Linux Kernel Functional Testing <lkft@linaro.org>
Acked-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
lib/kunit/Makefile | 3 ++
lib/kunit/backtrace-suppression-test.c | 90 ++++++++++++++++++++++++++++++++++
2 files changed, 93 insertions(+)
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index fe177ff3ebdef..b2f2b8ada7b71 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -23,6 +23,9 @@ obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
obj-$(CONFIG_KUNIT_TEST) += platform-test.o
+ifeq ($(CONFIG_KUNIT_SUPPRESS_BACKTRACE),y)
+obj-$(CONFIG_KUNIT_TEST) += backtrace-suppression-test.o
+endif
# string-stream-test compiles built-in only.
ifeq ($(CONFIG_KUNIT_TEST),y)
diff --git a/lib/kunit/backtrace-suppression-test.c b/lib/kunit/backtrace-suppression-test.c
new file mode 100644
index 0000000000000..2ba5dcb5fef35
--- /dev/null
+++ b/lib/kunit/backtrace-suppression-test.c
@@ -0,0 +1,90 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for suppressing warning tracebacks.
+ *
+ * Copyright (C) 2024, Guenter Roeck
+ * Author: Guenter Roeck <linux@roeck-us.net>
+ */
+
+#include <kunit/test.h>
+#include <linux/bug.h>
+
+static void backtrace_suppression_test_warn_direct(struct kunit *test)
+{
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ WARN(1, "This backtrace should be suppressed");
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static void trigger_backtrace_warn(void)
+{
+ WARN(1, "This backtrace should be suppressed");
+}
+
+static void backtrace_suppression_test_warn_indirect(struct kunit *test)
+{
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ trigger_backtrace_warn();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static void backtrace_suppression_test_warn_multi(struct kunit *test)
+{
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ WARN(1, "This backtrace should be suppressed");
+ trigger_backtrace_warn();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 2);
+}
+
+static void backtrace_suppression_test_warn_on_direct(struct kunit *test)
+{
+ if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE) && !IS_ENABLED(CONFIG_KALLSYMS))
+ kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE or CONFIG_KALLSYMS");
+
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ WARN_ON(1);
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static void trigger_backtrace_warn_on(void)
+{
+ WARN_ON(1);
+}
+
+static void backtrace_suppression_test_warn_on_indirect(struct kunit *test)
+{
+ if (!IS_ENABLED(CONFIG_DEBUG_BUGVERBOSE))
+ kunit_skip(test, "requires CONFIG_DEBUG_BUGVERBOSE");
+
+ KUNIT_START_SUPPRESSED_WARNING(test);
+ trigger_backtrace_warn_on();
+ KUNIT_END_SUPPRESSED_WARNING(test);
+
+ KUNIT_EXPECT_EQ(test, KUNIT_SUPPRESSED_WARNING_COUNT(), 1);
+}
+
+static struct kunit_case backtrace_suppression_test_cases[] = {
+ KUNIT_CASE(backtrace_suppression_test_warn_direct),
+ KUNIT_CASE(backtrace_suppression_test_warn_indirect),
+ KUNIT_CASE(backtrace_suppression_test_warn_multi),
+ KUNIT_CASE(backtrace_suppression_test_warn_on_direct),
+ KUNIT_CASE(backtrace_suppression_test_warn_on_indirect),
+ {}
+};
+
+static struct kunit_suite backtrace_suppression_test_suite = {
+ .name = "backtrace-suppression-test",
+ .test_cases = backtrace_suppression_test_cases,
+};
+kunit_test_suites(&backtrace_suppression_test_suite);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("KUnit test to verify warning backtrace suppression");
--
2.52.0
^ permalink raw reply related
* [PATCH v7 2/5] bug/kunit: Reduce runtime impact of warning backtrace suppression
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Alessandro Carminati, Albert Esteve
In-Reply-To: <20260420-kunit_add_support-v7-0-e8bc6e0f70de@redhat.com>
From: Alessandro Carminati <acarmina@redhat.com>
KUnit support is not consistently present across distributions, some
include it in their stock kernels, while others do not.
While both KUNIT and KUNIT_SUPPRESS_BACKTRACE can be considered debug
features, the fact that some distros ship with KUnit enabled means it's
important to minimize the runtime impact of this patch.
To that end, this patch adds an atomic counter that tracks the number
of active suppressions. __kunit_is_suppressed_warning() checks this
counter first and returns immediately when no suppressions are active,
avoiding RCU-protected list traversal in the common case.
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
lib/kunit/bug.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
index 356c8a5928828..a7a88f0670d44 100644
--- a/lib/kunit/bug.c
+++ b/lib/kunit/bug.c
@@ -8,6 +8,7 @@
#include <kunit/bug.h>
#include <kunit/resource.h>
+#include <linux/atomic.h>
#include <linux/export.h>
#include <linux/rculist.h>
#include <linux/sched.h>
@@ -15,11 +16,13 @@
#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
static LIST_HEAD(suppressed_warnings);
+static atomic_t suppressed_warnings_cnt = ATOMIC_INIT(0);
static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
{
list_del_rcu(&warning->node);
synchronize_rcu(); /* Wait for readers to finish */
+ atomic_dec(&suppressed_warnings_cnt);
}
KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
@@ -37,6 +40,7 @@ __kunit_start_suppress_warning(struct kunit *test)
return NULL;
warning->task = current;
+ atomic_inc(&suppressed_warnings_cnt);
list_add_rcu(&warning->node, &suppressed_warnings);
ret = kunit_add_action_or_reset(test,
@@ -68,6 +72,9 @@ bool __kunit_is_suppressed_warning(void)
{
struct __suppressed_warning *warning;
+ if (!atomic_read(&suppressed_warnings_cnt))
+ return false;
+
rcu_read_lock();
list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
if (warning->task == current) {
--
2.52.0
^ permalink raw reply related
* [PATCH v7 1/5] bug/kunit: Core support for suppressing warning backtraces
From: Albert Esteve @ 2026-04-20 12:28 UTC (permalink / raw)
To: Arnd Bergmann, Brendan Higgins, David Gow, Rae Moar,
Maarten Lankhorst, Maxime Ripard, Thomas Zimmermann, David Airlie,
Simona Vetter, Jonathan Corbet, Shuah Khan, Andrew Morton
Cc: linux-kernel, linux-arch, linux-kselftest, kunit-dev, dri-devel,
workflows, linux-doc, peterz, Alessandro Carminati, Guenter Roeck,
Kees Cook, Albert Esteve
In-Reply-To: <20260420-kunit_add_support-v7-0-e8bc6e0f70de@redhat.com>
From: Alessandro Carminati <acarmina@redhat.com>
Some unit tests intentionally trigger warning backtraces by passing bad
parameters to kernel API functions. Such unit tests typically check the
return value from such calls, not the existence of the warning backtrace.
Such intentionally generated warning backtraces are neither desirable
nor useful for a number of reasons:
- They can result in overlooked real problems.
- A warning that suddenly starts to show up in unit tests needs to be
investigated and has to be marked to be ignored, for example by
adjusting filter scripts. Such filters are ad hoc because there is
no real standard format for warnings. On top of that, such filter
scripts would require constant maintenance.
Solve the problem by providing a means to identify and suppress specific
warning backtraces while executing test code. Support suppressing multiple
backtraces while at the same time limiting changes to generic code to the
absolute minimum.
Implementation details:
Suppression is checked at two points in the warning path:
- In warn_slowpath_fmt(), the check runs before any output, fully
suppressing both message and backtrace.
- In __report_bug(), the check runs before __warn() is called,
suppressing the backtrace and stack dump. Note that on this path,
the WARN() format message may still appear in the kernel log since
__warn_printk() runs before the trap that enters __report_bug().
A helper function, `__kunit_is_suppressed_warning()`, walks an
RCU-protected list of active suppressions, matching by current task.
The suppression state is tied to the KUnit test lifecycle via
kunit_add_action(), ensuring automatic cleanup at test exit.
The list of suppressed warnings is protected with RCU to allow
concurrent read access without locks.
The implementation is deliberately simple and avoids architecture-specific
optimizations to preserve portability.
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Alessandro Carminati <acarmina@redhat.com>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Albert Esteve <aesteve@redhat.com>
---
include/kunit/bug.h | 56 +++++++++++++++++++++++++++++++++++
include/kunit/test.h | 1 +
kernel/panic.c | 8 ++++-
lib/bug.c | 8 +++++
lib/kunit/Kconfig | 9 ++++++
lib/kunit/Makefile | 6 ++--
lib/kunit/bug.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++
7 files changed, 169 insertions(+), 3 deletions(-)
diff --git a/include/kunit/bug.h b/include/kunit/bug.h
new file mode 100644
index 0000000000000..e52c9d21d9fe6
--- /dev/null
+++ b/include/kunit/bug.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * KUnit helpers for backtrace suppression
+ *
+ * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
+ * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
+ */
+
+#ifndef _KUNIT_BUG_H
+#define _KUNIT_BUG_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/kconfig.h>
+
+struct kunit;
+
+#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
+
+#include <linux/types.h>
+
+struct task_struct;
+
+struct __suppressed_warning {
+ struct list_head node;
+ struct task_struct *task;
+ int counter;
+};
+
+struct __suppressed_warning *
+__kunit_start_suppress_warning(struct kunit *test);
+void __kunit_end_suppress_warning(struct kunit *test,
+ struct __suppressed_warning *warning);
+int __kunit_suppressed_warning_count(struct __suppressed_warning *warning);
+bool __kunit_is_suppressed_warning(void);
+
+#define KUNIT_START_SUPPRESSED_WARNING(test) \
+ struct __suppressed_warning *__kunit_suppress = \
+ __kunit_start_suppress_warning(test)
+
+#define KUNIT_END_SUPPRESSED_WARNING(test) \
+ __kunit_end_suppress_warning(test, __kunit_suppress)
+
+#define KUNIT_SUPPRESSED_WARNING_COUNT() \
+ __kunit_suppressed_warning_count(__kunit_suppress)
+
+#else /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
+
+#define KUNIT_START_SUPPRESSED_WARNING(test)
+#define KUNIT_END_SUPPRESSED_WARNING(test)
+#define KUNIT_SUPPRESSED_WARNING_COUNT() 0
+static inline bool __kunit_is_suppressed_warning(void) { return false; }
+
+#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
+#endif /* __ASSEMBLY__ */
+#endif /* _KUNIT_BUG_H */
diff --git a/include/kunit/test.h b/include/kunit/test.h
index 9cd1594ab697d..4ec07b3fa0204 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -10,6 +10,7 @@
#define _KUNIT_TEST_H
#include <kunit/assert.h>
+#include <kunit/bug.h>
#include <kunit/try-catch.h>
#include <linux/args.h>
diff --git a/kernel/panic.c b/kernel/panic.c
index c78600212b6c1..d7a7a679f56c4 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -39,6 +39,7 @@
#include <linux/sys_info.h>
#include <trace/events/error_report.h>
#include <asm/sections.h>
+#include <kunit/bug.h>
#define PANIC_TIMER_STEP 100
#define PANIC_BLINK_SPD 18
@@ -1080,9 +1081,14 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
void warn_slowpath_fmt(const char *file, int line, unsigned taint,
const char *fmt, ...)
{
- bool rcu = warn_rcu_enter();
+ bool rcu;
struct warn_args args;
+ if (__kunit_is_suppressed_warning())
+ return;
+
+ rcu = warn_rcu_enter();
+
pr_warn(CUT_HERE);
if (!fmt) {
diff --git a/lib/bug.c b/lib/bug.c
index 623c467a8b76c..606205c8c302f 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -48,6 +48,7 @@
#include <linux/rculist.h>
#include <linux/ftrace.h>
#include <linux/context_tracking.h>
+#include <kunit/bug.h>
extern struct bug_entry __start___bug_table[], __stop___bug_table[];
@@ -223,6 +224,13 @@ static enum bug_trap_type __report_bug(struct bug_entry *bug, unsigned long buga
no_cut = bug->flags & BUGFLAG_NO_CUT_HERE;
has_args = bug->flags & BUGFLAG_ARGS;
+ /*
+ * Before the once logic so suppressed warnings do not consume
+ * the single-fire budget of WARN_ON_ONCE().
+ */
+ if (warning && __kunit_is_suppressed_warning())
+ return BUG_TRAP_TYPE_WARN;
+
if (warning && once) {
if (done)
return BUG_TRAP_TYPE_WARN;
diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
index 498cc51e493dc..57527418fcf09 100644
--- a/lib/kunit/Kconfig
+++ b/lib/kunit/Kconfig
@@ -15,6 +15,15 @@ menuconfig KUNIT
if KUNIT
+config KUNIT_SUPPRESS_BACKTRACE
+ bool "KUnit - Enable backtrace suppression"
+ default y
+ help
+ Enable backtrace suppression for KUnit. If enabled, backtraces
+ generated intentionally by KUnit tests are suppressed. Disable
+ to reduce kernel image size if image size is more important than
+ suppression of backtraces generated by KUnit tests.
+
config KUNIT_DEBUGFS
bool "KUnit - Enable /sys/kernel/debug/kunit debugfs representation" if !KUNIT_ALL_TESTS
default KUNIT_ALL_TESTS
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index 656f1fa35abcc..fe177ff3ebdef 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -16,8 +16,10 @@ ifeq ($(CONFIG_KUNIT_DEBUGFS),y)
kunit-objs += debugfs.o
endif
-# KUnit 'hooks' are built-in even when KUnit is built as a module.
-obj-$(if $(CONFIG_KUNIT),y) += hooks.o
+# KUnit 'hooks' and bug handling are built-in even when KUnit is built
+# as a module.
+obj-$(if $(CONFIG_KUNIT),y) += hooks.o \
+ bug.o
obj-$(CONFIG_KUNIT_TEST) += kunit-test.o
obj-$(CONFIG_KUNIT_TEST) += platform-test.o
diff --git a/lib/kunit/bug.c b/lib/kunit/bug.c
new file mode 100644
index 0000000000000..356c8a5928828
--- /dev/null
+++ b/lib/kunit/bug.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit helpers for backtrace suppression
+ *
+ * Copyright (C) 2025 Alessandro Carminati <acarmina@redhat.com>
+ * Copyright (C) 2024 Guenter Roeck <linux@roeck-us.net>
+ */
+
+#include <kunit/bug.h>
+#include <kunit/resource.h>
+#include <linux/export.h>
+#include <linux/rculist.h>
+#include <linux/sched.h>
+
+#ifdef CONFIG_KUNIT_SUPPRESS_BACKTRACE
+
+static LIST_HEAD(suppressed_warnings);
+
+static void __kunit_suppress_warning_remove(struct __suppressed_warning *warning)
+{
+ list_del_rcu(&warning->node);
+ synchronize_rcu(); /* Wait for readers to finish */
+}
+
+KUNIT_DEFINE_ACTION_WRAPPER(__kunit_suppress_warning_cleanup,
+ __kunit_suppress_warning_remove,
+ struct __suppressed_warning *);
+
+struct __suppressed_warning *
+__kunit_start_suppress_warning(struct kunit *test)
+{
+ struct __suppressed_warning *warning;
+ int ret;
+
+ warning = kunit_kzalloc(test, sizeof(*warning), GFP_KERNEL);
+ if (!warning)
+ return NULL;
+
+ warning->task = current;
+ list_add_rcu(&warning->node, &suppressed_warnings);
+
+ ret = kunit_add_action_or_reset(test,
+ __kunit_suppress_warning_cleanup,
+ warning);
+ if (ret)
+ return NULL;
+
+ return warning;
+}
+EXPORT_SYMBOL_GPL(__kunit_start_suppress_warning);
+
+void __kunit_end_suppress_warning(struct kunit *test,
+ struct __suppressed_warning *warning)
+{
+ if (!warning)
+ return;
+ kunit_release_action(test, __kunit_suppress_warning_cleanup, warning);
+}
+EXPORT_SYMBOL_GPL(__kunit_end_suppress_warning);
+
+int __kunit_suppressed_warning_count(struct __suppressed_warning *warning)
+{
+ return warning ? warning->counter : 0;
+}
+EXPORT_SYMBOL_GPL(__kunit_suppressed_warning_count);
+
+bool __kunit_is_suppressed_warning(void)
+{
+ struct __suppressed_warning *warning;
+
+ rcu_read_lock();
+ list_for_each_entry_rcu(warning, &suppressed_warnings, node) {
+ if (warning->task == current) {
+ warning->counter++;
+ rcu_read_unlock();
+ return true;
+ }
+ }
+ rcu_read_unlock();
+
+ return false;
+}
+
+#endif /* CONFIG_KUNIT_SUPPRESS_BACKTRACE */
--
2.52.0
^ permalink raw reply related
page: next (older) | prev (newer) | latest
- recent:[subjects (threaded)|topics (new)|topics (active)]
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox