On 8/15/23 13:54, Petr Mladek wrote:
Adding workqueue and lockdep people into Cc.
On Fri 2023-08-11 19:11:46, Helge Deller wrote:
Fully initialize detector_work work struct to avoid this kernel warning
when lockdep is enabled:
=====================================
WARNING: bad unlock balance detected!
6.5.0-rc5+ #687 Not tainted
-------------------------------------
swapper/0/1 is trying to release lock (detector_work) at:
[<000000004037e554>] __flush_work+0x60/0x658
but there are no more locks to release!
other info that might help us debug this:
no locks held by swapper/0/1.
stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.5.0-rc5+ #687
Hardware name: 9000/785/C3700
Backtrace:
[<0000000041455d5c>] print_unlock_imbalance_bug.part.0+0x20c/0x230
[<000000004040d5e8>] lock_release+0x2e8/0x3f8
[<000000004037e5cc>] __flush_work+0xd8/0x658
[<000000004037eb7c>] flush_work+0x30/0x60
[<000000004011f140>] lockup_detector_check+0x54/0x128
[<0000000040306430>] do_one_initcall+0x9c/0x408
[<0000000040102d44>] kernel_init_freeable+0x688/0x7f0
[<000000004146df68>] kernel_init+0x64/0x3a8
[<0000000040302020>] ret_from_kernel_thread+0x20/0x28
Signed-off-by: Helge Deller <deller@xxxxxx>
---
diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index be38276a365f..eab0dfcfa3f9 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -1022,5 +1022,6 @@ void __init lockup_detector_init(void)
else
allow_lockup_detector_init_retry = true;
+ INIT_WORK(&detector_work, lockup_detector_delay_init);
lockup_detector_setup();
}
Strange. The work is initialized when declared:
static struct work_struct detector_work __initdata =
__WORK_INITIALIZER(detector_work, lockup_detector_delay_init);
, which should initialize the lockdep map as well. I would expect
this is enough.
Right. It's enough...
And I do not see this on x86_64 with CONFIG_PROVE_LOCKING=y
on today's Linus' tree. And the flush_work() is always called
from the lockup_detector_check() late init call.
IMHO, it must be a bug somewhere else. Otherwise, many other
users of DECLARE_WORK() or __WORK_INITIALIZER() would have
the same problem.
Right. I should have replied earlier to this patch.
Andrew already dropped this patch here from his patch collection.
It turns out the problem is in function static_obj() from
lockdep, which doesn't recognize the __initdata section
for all platforms.
Please look at this patch on the LKML instead, which
fixes the real problem:
[PATCH v2] lockdep: Fix static memory detection even more
Thanks!
Helge
