Le 27/02/2026 à 5:40 PM, Andy Shevchenko a écrit :
Hi!
I have stumbled over the kunit framework issues that make the respective test
cases useless.
Now to the details.
Consider having today's Linux Next.
Hi Andy,
Sorry to hear that KUnit is causing trouble. It looks like this is due
to those patches crashing the kernel before KUnit gets to run: by using
the --raw_output=full argument to kunit.py run, the corresponding logs
are shown.
Scenario 1 (good):
I run
./tools/testing/kunit/kunit.py config
./tools/testing/kunit/kunit.py run printf
Everything works as expected:
[10:19:36] Testing complete. Ran 28 tests: passed: 28
[10:19:36] Elapsed time: 15.929s total, 0.001s configuring, 15.761s
building, 0.114s running
This works fine for me, too. :-)
Scenario 2 (BAD):
I applied the following change:
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -18,6 +18,7 @@
*/
#include <linux/stdarg.h>
+#include <linux/bitops.h>
#include <linux/build_bug.h>
#include <linux/clk.h>
#include <linux/clk-provider.h>
@@ -2904,12 +2889,17 @@ int vsnprintf(char *buf, size_t size, const char
*fmt_str, va_list args)
case FORMAT_STATE_NUM: {
unsigned long long num;
+ u8 shift = fmt.size * 8 - 1;
if (fmt.size > sizeof(int))
num = va_arg(args, long long);
else
- num = convert_num_spec(va_arg(args, int),
fmt.size, spec);
- str = number(str, end, num, spec);
+ num = va_arg(args, int);
+ num = sign_extend64(num, shift);
+ if (spec.flags & SIGN)
+ str = number(str, end, num, spec);
+ else
+ str = number(str, end, -(long long)num, spec);
continue;
}
Tests went into cosmos (I waited a few minutes and has to interrupt that):
^CERROR:root:Build interruption occurred. Cleaning console.
^CERROR:root:Build interruption occurred. Cleaning console.
^CERROR:root:Build interruption occurred. Cleaning console.
Command '['.kunit/linux', 'kunit.filter_glob=printf', 'kunit.enable=1',
'mem=1G', 'console=tty', 'kunit_shutdown=halt']' timed out after 300 seconds
[10:29:52] [ERROR] Test: <missing>: Could not find any KTAP output. Did any
KUnit tests run?
[10:29:52] ============================================================
[10:29:52] Testing complete. Ran 0 tests: errors: 1
[10:29:52] Elapsed time: 305.676s total, 0.001s configuring, 5.669s
building, 300.006s running
NOTE!
Independently on how long I waited the Elapsed time is about 5 minutes
(Seems 300 seconds limit as stated in the output).
Interesting: this crashed immediately on my machine. During building, I
see a (harmless) warning:
../lib/vsprintf.c:2827:27: warning: ‘convert_num_spec’ defined but not
used [-Wunused-function]
By running KUnit with the --raw_output=full option, I can see a segfault
(though, as you can see, the numbers throughout the stacktrace a wrong):
<18446744073709551610>Pid: 1, comm: swapper/0 Not tainted
7.0.0-rc1-gff0627514551-dirty
<18446744073709551610>RIP: ffffffffffffffcd:0xffffffff9fac7320
<18446744073709551610>RSP: ffffffff5f7fc098 EFLAGS: fffffffffffefdf9
<18446744073709551610>RAX: fffffffffffc0000 RBX: ffffffff9ff1ad4c RCX:
ffffffff9f7b6440
<18446744073709551610>RDX: 0000000000000000 RSI: ffffffff9f7b6388 RDI:
ffffffffc6cfc8cc
<18446744073709551610>RBP: 0000000000000000 R08: ffffffffffffffff R09:
ffffffffffffffd0
<18446744073709551610>R10: fffffffffffffff8 R11: fffffffffffffdba R12:
ffffffff9fac7320
<18446744073709551610>R13: ffffffff9ff1b0d0 R14: 0000000000000000 R15:
ffffffff9f963fe8
<0>Kernel panic - not syncing: Segfault with no mm
<18446744073709551612>CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted
7.0.0-rc1-gff0627514551-dirty #35 VOLUNTARY
<18446744073709551612>Stack:
<18446744073709551612> ffffffff9fbe2fd0 00000000 ffffffff9fffdaec
ffffffff5f7fc080
<18446744073709551612> ffffffff5f7fc080 ffffffff9ff95050
ffffffff9fab1be0 ffffffff9ff95050
<18446744073709551612> ffffffff9fbe2fd0 00000000 00000000 00000000
<18446744073709551612>Call Trace:
<18446744073709551612> [<ffffffff9fbe2fd0>] ?
kernel_init+0x0/0xfffffffffffffe20
<18446744073709551612> [<ffffffff9fffdaec>] ?
kernel_init_freeable+0xfffffffffffffe8b/0xfffffffffffffc82
<18446744073709551612> [<ffffffff9ff95050>] ?
uml_curr_cpu+0x0/0xfffffffffffffff0
<18446744073709551612> [<ffffffff9ff95050>] ?
uml_curr_cpu+0x0/0xfffffffffffffff0
<18446744073709551612> [<ffffffff9fbe2fd0>] ?
kernel_init+0x0/0xfffffffffffffe20
<18446744073709551612> [<ffffffff9fbe2faa>] ?
kernel_init+0xffffffffffffffda/0xfffffffffffffe20
<18446744073709551612> [<ffffffff9ff95050>] ?
uml_curr_cpu+0x0/0xfffffffffffffff0
<18446744073709551612> [<ffffffff9ffa5c27>] ?
new_thread_handler+0xffffffffffffff87/0xffffffffffffff60
(Trying the same thing with --arch x86_64 suggested that some stack
corruption is occurring.)
Scenario 3 (BAD):
Now I took again a clean tree and applied this change:
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -18,6 +18,7 @@
*/
#include <linux/stdarg.h>
+#include <linux/bitops.h>
#include <linux/build_bug.h>
#include <linux/clk.h>
#include <linux/clk-provider.h>
@@ -2904,11 +2889,17 @@ int vsnprintf(char *buf, size_t size, const char
*fmt_str, va_list args)
case FORMAT_STATE_NUM: {
unsigned long long num;
+ u8 shift = fmt.size * 8 - 1;
if (fmt.size > sizeof(int))
num = va_arg(args, long long);
+ else {
+ num = va_arg(args, int);
+ if ((spec.flags & SIGN))
+ num = sign_extend64(num, shift);
else
- num = convert_num_spec(va_arg(args, int),
fmt.size, spec);
+ num &= ~(BIT_ULL(shift) - 1);
+ }
str = number(str, end, num, spec);
continue;
}
and run tests again.
[10:39:16] [ERROR] Test: <missing>: Could not find any KTAP output. Did any
KUnit tests run?
[10:39:16] ============================================================
[10:39:16] Testing complete. Ran 0 tests: errors: 1
[10:39:16] Elapsed time: 5.762s total, 0.001s configuring, 5.694s building,
0.067s running
it runs fast and completely useless. (There is no build error)
This one also kernel panics, and when run with --raw_output=full, we can
see that it's due to all of the character devices' sysfs entries being
duplicates, because the minor/major are being formatted as '/dev/char/0:0':
<0>sysfs: cannot create duplicate filename '/dev/char/0:0'
(...)
<0>Kernel panic - not syncing: Couldn't register pty driver
<0>CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W
7.0.0-rc1-gff0627514551-dirty #34 VOLUNTARY
...
Please, fix this as it is a serious issue and really makes kunit useless.
There's not much KUnit can do if the kernel panics before any tests can
be run -- and unfortunately, vsprintf() seems able to cause lots of
trouble early in the boot process.
One idea is to support building tests as independent userspace
executables, which wouldn't depend on all of those parts of the kernel
which break (and would be easier to debug). I discussed this a bit at
Plumbers a couple of years ago[1], but haven't had a chance to work on
it since. Even then, it'd require a little bit of test-specific work to
get an isolated version of the kernel vsprintf to build and be testable.
In the short term, maybe we can improve the interface of kunit.py in
cases where the kernel crashes. At the moment, we simply report that no
tests had run (as you've noticed), but maybe we should check more
actively for panics and/or make a more explicit difference between "no
tests were run" and "the KUnit framework never exectuted". At the very
least, we should suggest that --raw_output=full is a good way to debug
this issue if the user wasn't expecting it in the error message. (I'll
send a patch out to do this now.)
I hope that helps (at least a little bit), and thanks for sticking with
KUnit despite these issues!
Cheers,
-- David
[1]: https://lpc.events/event/18/contributions/1790/
