linux-kernel - Re: [PATCH] lockdep: Have assert functions test for actual interrupts disabled

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Date:   Wed, 5 Sep 2018 11:20:31 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH] lockdep: Have assert functions test for actual
 interrupts disabled


Peter, you OK with this patch? I'm currently triggering a bug (in rc2)
where this patch is telling me that lockdep is getting it wrong. It
would be good to have this upstream such that we know if it is really a
bug in the code itself, or if lockdep didn't keep up properly.

-- Steve


On Mon, 6 Aug 2018 21:41:07 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: Steven Rostedt (VMware) <rostedt@...dmis.org>
> 
> While working on irqs disabled tracepoints, I triggered the following
> warning:
> 
>  ------------[ cut here ]------------
>  IRQs not disabled as expected
>  WARNING: CPU: 0 PID: 0 at kernel/softirq.c:144 __local_bh_enable+0x9b/0xe0
>  Modules linked in:
>  CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W         4.18.0-rc6-test+ #1099
>  Hardware name: Hewlett-Packard HP Compaq Pro 6300 SFF/339A, BIOS K01 v03.03 07/14/2016
>  RIP: 0010:__local_bh_enable+0x9b/0xe0
>  Code: 5b d2 30 00 8b 85 98 08 00 00 85 c0 74 bf 80 3d ff eb 06 02 00 75 b6 48 c7 c7 80 89 46 8c c6 05 ef eb 06 02 01 e8 15 4e ff ff <0f> 0b eb 9f 48 8b 7c 24 10 e8 67 5f 09 00 eb b2 48 8b 6c 24 10 48 
>  RSP: 0018:ffff8800d3e07f50 EFLAGS: 00010082
>  RAX: 0000000000000000 RBX: 0000000000000100 RCX: 0000000000000000
>  RDX: 0000000000000102 RSI: dffffc0000000000 RDI: ffffffff8e57dc00
>  RBP: ffffffff8cc1f980 R08: fffffbfff199f449 R09: fffffbfff199f448
>  R10: ffff8800d3e2643f R11: ffffed001a7c4c88 R12: 0000000000000007
>  R13: 0000000000000008 R14: 0000000000000007 R15: 0000000000000000
>  FS:  0000000000000000(0000) GS:ffff8800d3e00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000000000 CR3: 00000000cac14001 CR4: 00000000001606f0
>  Call Trace:
>   <IRQ>
>   __do_softirq+0x4a0/0x55a
>   irq_exit+0x128/0x130
>   reschedule_interrupt+0xf/0x20
>   </IRQ>
>  RIP: 0010:cpuidle_enter_state+0xcc/0x430
>  Code: 63 55 ff 48 89 04 24 0f 1f 44 00 00 31 ff e8 7b 8d 55 ff 80 7c 24 10 00 0f 85 fb 02 00 00 e8 eb a8 69 ff fb 66 0f 1f 44 00 00 <4c> 8b 3c 24 4c 2b 7c 24 08 48 ba cf f7 53 e3 a5 9b c4 20 48 8d 7b 
>  RSP: 0018:ffffffff8cc07d18 EFLAGS: 00000282 ORIG_RAX: ffffffffffffff02
>  RAX: 0000000000025140 RBX: ffff8800d3e34f00 RCX: ffffffff8b1cec2e
>  RDX: dffffc0000000000 RSI: 0000000000000001 RDI: ffffffff8cd4a868
>  RBP: ffffffff8cf1b660 R08: ffffed001a7c43db R09: 0000000000000000
>  R10: ffff8800d3e2643f R11: ffffed001a7c4c88 R12: ffffffff8cf1b7f8
>  R13: 0000000000000004 R14: ffffffff8cf1b7e0 R15: ffffffff8cf1b820
>   ? __srcu_read_unlock+0x1e/0x40
>   ? cpuidle_enter_state+0xc5/0x430
>   do_idle+0x28f/0x300
>   ? arch_cpu_idle_exit+0x40/0x40
>   ? schedule_idle+0x39/0x50
>   cpu_startup_entry+0xc2/0xd0
>   ? cpu_in_idle+0x20/0x20
>   ? preempt_count_sub+0xaa/0x100
>   ? preempt_count_add+0xaf/0xd0
>   start_kernel+0x640/0x67d
>   ? thread_stack_cache_init+0x6/0x6
>   ? load_ucode_intel_bsp+0x5f/0xa5
>   ? load_ucode_intel_bsp+0x5f/0xa5
>   ? init_intel_microcode+0xb0/0xb0
>   ? load_ucode_bsp+0xbb/0x156
>   secondary_startup_64+0xa5/0xb0
>  irq event stamp: 9229434
>  hardirqs last  enabled at (9229434): [<ffffffff8b004453>] trace_hardirqs_on_thunk+0x1a/0x1c
>  hardirqs last disabled at (9229433): [<ffffffff8b00446f>] trace_hardirqs_off_thunk+0x1a/0x1c
>  softirqs last  enabled at (9229416): [<ffffffff8b10d35c>] irq_enter+0x7c/0x80
>  softirqs last disabled at (9229417): [<ffffffff8b10d488>] irq_exit+0x128/0x130
>  ---[ end trace 35ba8f92a3c06fd6 ]---
>  ------------[ cut here ]------------
> 
> When investigating, I found that interrupts were actually disabled, but
> the bug was that lockdep was confused. As the asserts for expecting
> interrupts disabled is now done by lockdep state tracking, it would be
> nice to know if the bug is the interrupts not being disabled or lockdep
> just thinking that they are disabled. Add a check within the WARN_ON()
> to do the actual irqs_disabled() check (which only gets done when
> lockdep thinks there's an error), and show that lockdep is broken if it
> does not match up with the real state of interrupts.
> 
> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ----
> diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
> index a8113357ceeb..c50c80eea41d 100644
> --- a/include/linux/lockdep.h
> +++ b/include/linux/lockdep.h
> @@ -601,12 +601,16 @@ do {									\
>  #define lockdep_assert_irqs_enabled()	do {				\
>  		WARN_ONCE(debug_locks && !current->lockdep_recursion &&	\
>  			  !current->hardirqs_enabled,			\
> -			  "IRQs not enabled as expected\n");		\
> +			  irqs_disabled() ?				\
> +			  "IRQs not enabled as expected\n" :		\
> +			  "IRQs enabled but lockdep reports they are disabled\n"); \
>  	} while (0)
>  
>  #define lockdep_assert_irqs_disabled()	do {				\
>  		WARN_ONCE(debug_locks && !current->lockdep_recursion &&	\
>  			  current->hardirqs_enabled,			\
> +			  irqs_disabled() ?				\
> +			  "IRQs disabled but lockdep reports they are enabled\n" : \
>  			  "IRQs not disabled as expected\n");		\
>  	} while (0)
>