Messages in this thread | | | Date | Tue, 15 Aug 2023 14:44:25 +0200 | Subject | Re: [PATCH] watchdog: Fix lockdep warning | From | Helge Deller <> |
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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@gmx.de> >> >> --- >> >> 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
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