[PATCH net-next 1/2] selftests: net: py: capitalize defer queue and improve import

[PATCH net-next 1/2] selftests: net: py: capitalize defer queue and improve import

[Jakub Kicinski]

Import utils and refer to the global defer queue that way instead
of importing the queue. This will make it possible to assign value
to the global variable. While at it capitalize the name, to comply
with the Python coding style.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 tools/testing/selftests/net/lib/py/ksft.py  | 8 ++++----
 tools/testing/selftests/net/lib/py/utils.py | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/tools/testing/selftests/net/lib/py/ksft.py b/tools/testing/selftests/net/lib/py/ksft.py
index 531e7fa1b3ea..248cd1a723a3 100644
--- a/tools/testing/selftests/net/lib/py/ksft.py
+++ b/tools/testing/selftests/net/lib/py/ksft.py
@@ -8,7 +8,7 @@ import time
 import traceback
 from collections import namedtuple
 from .consts import KSFT_MAIN_NAME
-from .utils import global_defer_queue
+from . import utils
 
 KSFT_RESULT = None
 KSFT_RESULT_ALL = True
@@ -157,10 +157,10 @@ KSFT_DISRUPTIVE = True
     global KSFT_RESULT
 
     i = 0
-    qlen_start = len(global_defer_queue)
-    while global_defer_queue:
+    qlen_start = len(utils.GLOBAL_DEFER_QUEUE)
+    while utils.GLOBAL_DEFER_QUEUE:
         i += 1
-        entry = global_defer_queue.pop()
+        entry = utils.GLOBAL_DEFER_QUEUE.pop()
         try:
             entry.exec_only()
         except Exception:
diff --git a/tools/testing/selftests/net/lib/py/utils.py b/tools/testing/selftests/net/lib/py/utils.py
index 106ee1f2df86..2dde34560d65 100644
--- a/tools/testing/selftests/net/lib/py/utils.py
+++ b/tools/testing/selftests/net/lib/py/utils.py
@@ -141,7 +141,7 @@ import time
         return self.process(terminate=terminate, fail=self.check_fail)
 
 
-global_defer_queue = []
+GLOBAL_DEFER_QUEUE = []
 
 
 class defer:
@@ -153,7 +153,7 @@ global_defer_queue = []
         self.args = args
         self.kwargs = kwargs
 
-        self._queue =  global_defer_queue
+        self._queue = GLOBAL_DEFER_QUEUE
         self._queue.append(self)
 
     def __enter__(self):
-- 
2.52.0

[PATCH net-next 2/2] selftests: net: py: ensure defer() is only used within a test case

[Jakub Kicinski]

I wasted a couple of hours recently after accidentally adding
a defer() from within a function which itself was called as
part of defer(). This leads to an infinite loop of defer().
Make sure this cannot happen and raise a helpful exception.

I understand that the pair of _ksft_defer_arm() calls may
not be the most Pythonic way to implement this, but it's
easy enough to understand.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 tools/testing/selftests/net/lib/py/ksft.py  | 7 +++++++
 tools/testing/selftests/net/lib/py/utils.py | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/tools/testing/selftests/net/lib/py/ksft.py b/tools/testing/selftests/net/lib/py/ksft.py
index 248cd1a723a3..0a96f88bb60a 100644
--- a/tools/testing/selftests/net/lib/py/ksft.py
+++ b/tools/testing/selftests/net/lib/py/ksft.py
@@ -153,6 +153,11 @@ KSFT_DISRUPTIVE = True
     print(res, flush=True)
 
 
+def _ksft_defer_arm(state):
+    """ Allow or disallow the use of defer() """
+    utils.GLOBAL_DEFER_ARMED = state
+
+
 def ksft_flush_defer():
     global KSFT_RESULT
 
@@ -315,6 +320,7 @@ KsftCaseFunction = namedtuple("KsftCaseFunction",
         comment = ""
         cnt_key = ""
 
+        _ksft_defer_arm(True)
         try:
             func(*args)
         except KsftSkipEx as e:
@@ -332,6 +338,7 @@ KsftCaseFunction = namedtuple("KsftCaseFunction",
                 ksft_pr(f"Stopping tests due to {type(e).__name__}.")
             KSFT_RESULT = False
             cnt_key = 'fail'
+        _ksft_defer_arm(False)
 
         try:
             ksft_flush_defer()
diff --git a/tools/testing/selftests/net/lib/py/utils.py b/tools/testing/selftests/net/lib/py/utils.py
index 2dde34560d65..824f039d384c 100644
--- a/tools/testing/selftests/net/lib/py/utils.py
+++ b/tools/testing/selftests/net/lib/py/utils.py
@@ -142,6 +142,7 @@ import time
 
 
 GLOBAL_DEFER_QUEUE = []
+GLOBAL_DEFER_ARMED = False
 
 
 class defer:
@@ -153,6 +154,8 @@ GLOBAL_DEFER_QUEUE = []
         self.args = args
         self.kwargs = kwargs
 
+        if not GLOBAL_DEFER_ARMED:
+            raise Exception("defer queue not armed, did you use defer() outside of a test case?")
         self._queue = GLOBAL_DEFER_QUEUE
         self._queue.append(self)
 
-- 
2.52.0

Re: [PATCH net-next 2/2] selftests: net: py: ensure defer() is only used within a test case

[Petr Machata]

Jakub Kicinski <kuba@kernel.org> writes:

> I wasted a couple of hours recently after accidentally adding
> a defer() from within a function which itself was called as
> part of defer(). This leads to an infinite loop of defer().
> Make sure this cannot happen and raise a helpful exception.
>
> I understand that the pair of _ksft_defer_arm() calls may
> not be the most Pythonic way to implement this, but it's
> easy enough to understand.
>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

I think we achieve the same without the extra globals though? Just drain
the queue and walk through a copy of it?

    defer_queue = utils.GLOBAL_DEFER_QUEUE
    utils.GLOBAL_DEFER_QUEUE = []
    for i, entry in enumerate(defer_queue):
        ...
    if utils.GLOBAL_DEFER_QUEUE:
        warning / exception

> ---
>  tools/testing/selftests/net/lib/py/ksft.py  | 7 +++++++
>  tools/testing/selftests/net/lib/py/utils.py | 3 +++
>  2 files changed, 10 insertions(+)
>
> diff --git a/tools/testing/selftests/net/lib/py/ksft.py b/tools/testing/selftests/net/lib/py/ksft.py
> index 248cd1a723a3..0a96f88bb60a 100644
> --- a/tools/testing/selftests/net/lib/py/ksft.py
> +++ b/tools/testing/selftests/net/lib/py/ksft.py
> @@ -153,6 +153,11 @@ KSFT_DISRUPTIVE = True
>      print(res, flush=True)
>  
>  
> +def _ksft_defer_arm(state):
> +    """ Allow or disallow the use of defer() """
> +    utils.GLOBAL_DEFER_ARMED = state
> +
> +
>  def ksft_flush_defer():
>      global KSFT_RESULT
>  
> @@ -315,6 +320,7 @@ KsftCaseFunction = namedtuple("KsftCaseFunction",
>          comment = ""
>          cnt_key = ""
>  
> +        _ksft_defer_arm(True)
>          try:
>              func(*args)
>          except KsftSkipEx as e:
> @@ -332,6 +338,7 @@ KsftCaseFunction = namedtuple("KsftCaseFunction",
>                  ksft_pr(f"Stopping tests due to {type(e).__name__}.")
>              KSFT_RESULT = False
>              cnt_key = 'fail'
> +        _ksft_defer_arm(False)
>  
>          try:
>              ksft_flush_defer()
> diff --git a/tools/testing/selftests/net/lib/py/utils.py b/tools/testing/selftests/net/lib/py/utils.py
> index 2dde34560d65..824f039d384c 100644
> --- a/tools/testing/selftests/net/lib/py/utils.py
> +++ b/tools/testing/selftests/net/lib/py/utils.py
> @@ -142,6 +142,7 @@ import time
>  
>  
>  GLOBAL_DEFER_QUEUE = []
> +GLOBAL_DEFER_ARMED = False
>  
>  
>  class defer:
> @@ -153,6 +154,8 @@ GLOBAL_DEFER_QUEUE = []
>          self.args = args
>          self.kwargs = kwargs
>  
> +        if not GLOBAL_DEFER_ARMED:
> +            raise Exception("defer queue not armed, did you use defer() outside of a test case?")
>          self._queue = GLOBAL_DEFER_QUEUE
>          self._queue.append(self)

Re: [PATCH net-next 2/2] selftests: net: py: ensure defer() is only used within a test case

[Jakub Kicinski]

On Fri, 9 Jan 2026 09:23:54 +0100 Petr Machata wrote:
> > I wasted a couple of hours recently after accidentally adding
> > a defer() from within a function which itself was called as
> > part of defer(). This leads to an infinite loop of defer().
> > Make sure this cannot happen and raise a helpful exception.
> >
> > I understand that the pair of _ksft_defer_arm() calls may
> > not be the most Pythonic way to implement this, but it's
> > easy enough to understand.
> >
> > Signed-off-by: Jakub Kicinski <kuba@kernel.org>  
> 
> I think we achieve the same without the extra globals though? Just drain
> the queue and walk through a copy of it?
> 
>     defer_queue = utils.GLOBAL_DEFER_QUEUE
>     utils.GLOBAL_DEFER_QUEUE = []
>     for i, entry in enumerate(defer_queue):
>         ...
>     if utils.GLOBAL_DEFER_QUEUE:
>         warning / exception

That's what I had initially (IIUC), I was assigning None to the queue,
and then [] only while inside a test case. It gets slightly hairy
because either we need to pass in the queue into the flush function;
or we have to restore the queue if something raises and exception during
flush (in which case ksft_run() prints a warning and calls
ksft_flush_defer() one more time).

That approach definitely worked, but unless I'm missing a trick it was
higher complexity and LoC.

Re: [PATCH net-next 2/2] selftests: net: py: ensure defer() is only used within a test case

[Petr Machata]

Jakub Kicinski <kuba@kernel.org> writes:

> On Fri, 9 Jan 2026 09:23:54 +0100 Petr Machata wrote:
>> > I wasted a couple of hours recently after accidentally adding
>> > a defer() from within a function which itself was called as
>> > part of defer(). This leads to an infinite loop of defer().
>> > Make sure this cannot happen and raise a helpful exception.
>> >
>> > I understand that the pair of _ksft_defer_arm() calls may
>> > not be the most Pythonic way to implement this, but it's
>> > easy enough to understand.
>> >
>> > Signed-off-by: Jakub Kicinski <kuba@kernel.org>  
>> 
>> I think we achieve the same without the extra globals though? Just drain
>> the queue and walk through a copy of it?
>> 
>>     defer_queue = utils.GLOBAL_DEFER_QUEUE
>>     utils.GLOBAL_DEFER_QUEUE = []
>>     for i, entry in enumerate(defer_queue):
>>         ...
>>     if utils.GLOBAL_DEFER_QUEUE:
>>         warning / exception
>
> That's what I had initially (IIUC), I was assigning None to the queue,
> and then [] only while inside a test case. It gets slightly hairy
> because either we need to pass in the queue into the flush function;
> or we have to restore the queue if something raises and exception during
> flush (in which case ksft_run() prints a warning and calls
> ksft_flush_defer() one more time).

Hmm, yeah, the exception robustness will complicate it. OK, let's have
it your way then :)

Reviewed-by: Petr Machata <petrm@nvidia.com>

Re: [PATCH net-next 1/2] selftests: net: py: capitalize defer queue and improve import

[Petr Machata]

Jakub Kicinski <kuba@kernel.org> writes:

> Import utils and refer to the global defer queue that way instead
> of importing the queue. This will make it possible to assign value
> to the global variable. While at it capitalize the name, to comply
> with the Python coding style.
>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Petr Machata <petrm@nvidia.com>

Re: [PATCH net-next 1/2] selftests: net: py: capitalize defer queue and improve import

[Breno Leitao]

On Thu, Jan 08, 2026 at 02:52:56PM -0800, Jakub Kicinski wrote:
> Import utils and refer to the global defer queue that way instead
> of importing the queue. This will make it possible to assign value
> to the global variable. While at it capitalize the name, to comply
> with the Python coding style.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviwed-by: Breno Leitao <leitao@debian.org>

Re: [PATCH net-next 1/2] selftests: net: py: capitalize defer queue and improve import

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu,  8 Jan 2026 14:52:56 -0800 you wrote:
> Import utils and refer to the global defer queue that way instead
> of importing the queue. This will make it possible to assign value
> to the global variable. While at it capitalize the name, to comply
> with the Python coding style.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> 
> [...]

Here is the summary with links:
  - [net-next,1/2] selftests: net: py: capitalize defer queue and improve import
    https://git.kernel.org/netdev/net-next/c/799a4912eea7
  - [net-next,2/2] selftests: net: py: ensure defer() is only used within a test case
    https://git.kernel.org/netdev/net-next/c/7a1ff3545ade

You are awesome, thank you!
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