Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection

[Peter Zijlstra <peterz@infradead.org>]

On Fri, 2009-04-17 at 00:16 -0400, Steven Rostedt wrote:
> Here's the dump that I get that triggers the lockdep warning:
> 
> WARNING: at kernel/lockdep.c:2893 check_flags+0x1a7/0x1d0()
> Hardware name: Precision WorkStation 470    
> Modules linked in: radeon drm autofs4 hidp rfcomm l2cap bluetooth sunrpc 
> 
> [snip]
> 
> Pid: 3768, comm: sshd Not tainted 2.6.30-rc1 #1036
> Call Trace:
>  [<ffffffff8025c321>] warn_slowpath+0xe1/0x110
>  [<ffffffff80287f7c>] ? __lock_acquire+0x3ac/0xb20
>  [<ffffffff80286dca>] ? validate_chain+0x4ca/0x12d0
>  [<ffffffff80286dca>] ? validate_chain+0x4ca/0x12d0
>  [<ffffffff80286dca>] ? validate_chain+0x4ca/0x12d0
>  [<ffffffff80286dca>] ? validate_chain+0x4ca/0x12d0
>  [<ffffffff80287f7c>] ? __lock_acquire+0x3ac/0xb20
>  [<ffffffff8051a5a9>] ? __alloc_skb+0x49/0x160
>  [<ffffffff80282407>] check_flags+0x1a7/0x1d0
>  [<ffffffff80284d63>] lockdep_trace_alloc+0x33/0xe0
>  [<ffffffff802f3682>] kmem_cache_alloc+0x32/0x160
>  [<ffffffff8051a5a9>] __alloc_skb+0x49/0x160
>  [<ffffffff8059192d>] tcp_send_ack+0x2d/0xe0
>  [<ffffffff8058e941>] __tcp_ack_snd_check+0x61/0xb0
>  [<ffffffff80590408>] tcp_rcv_established+0x398/0x600
>  [<ffffffff80596a58>] tcp_v4_do_rcv+0x228/0x380
>  [<ffffffff80228ed6>] ? ftrace_call+0x5/0x2b
>  [<ffffffff8058454e>] ? tcp_prequeue_process+0x2e/0xa0
>  [<ffffffff8058458d>] tcp_prequeue_process+0x6d/0xa0
>  [<ffffffff8058734a>] tcp_recvmsg+0x49a/0x880
>  [<ffffffff80514267>] sock_common_recvmsg+0x37/0x50
>  [<ffffffff805116b9>] sock_aio_read+0x109/0x110
>  [<ffffffff802f75f1>] do_sync_read+0xf1/0x130
>  [<ffffffff8022ec33>] ? sched_clock+0x13/0x20
>  [<ffffffff8022ec5d>] ? native_sched_clock+0x1d/0x50
>  [<ffffffff802737d0>] ? autoremove_wake_function+0x0/0x40
>  [<ffffffff80228ed6>] ? ftrace_call+0x5/0x2b
>  [<ffffffff80381469>] ? cap_file_permission+0x9/0x10
>  [<ffffffff80380116>] ? security_file_permission+0x16/0x20
>  [<ffffffff802f7fc9>] vfs_read+0x159/0x170
>  [<ffffffff802f8285>] sys_read+0x55/0x90
>  [<ffffffff802291af>] system_call_fastpath+0x16/0x1b
> ---[ end trace 03d889e04bc7a9a7 ]---
> possible reason: unannotated irqs-on.
> irq event stamp: 12569
> hardirqs last  enabled at (12567): [<ffffffff8026206a>] local_bh_enable+0xaa/0x110
> hardirqs last disabled at (12569): [<ffffffff80610c76>] int3+0x16/0x40
> softirqs last  enabled at (12566): [<ffffffff80514d2b>] lock_sock_nested+0xfb/0x110
> softirqs last disabled at (12568): [<ffffffff8058454e>] tcp_prequeue_process+0x2e/0xa0
> 
> 
> Note, for some reason we hit int3 ??
> 
> Tracepoints do not use int3 does it?
> 
> I have kprobes defined but not any kprobe self tests on.

CONFIG_NET_TCPPROBE perhaps?

> Anyway, let me describe what the above is and what I found in my 
> investigation.
> 
> The lockdep took a check_flags error when it noticed that interrupts were 
> enabled, but the current->hardirqs_enabled was 0. Lockdep thought 
> interrupts were disabled but they were in fact enabled.
> 
> 
> The last 4 lines of the warning have the numbers in the parenthesis 
> annotate the order of events: (Here they are in order)
> 
> softirqs last  enabled at (12566): [<ffffffff80514d2b>] lock_sock_nested+0xfb/0x110
> hardirqs last  enabled at (12567): [<ffffffff8026206a>] local_bh_enable+0xaa/0x110
> softirqs last disabled at (12568): [<ffffffff8058454e>] tcp_prequeue_process+0x2e/0xa0
> hardirqs last disabled at (12569): [<ffffffff80610c76>] int3+0x16/0x40
> 
> The last change that lockdep saw was interrupts being disabled by int3. I 
> still don't understand why int3 was enabled. I have startup tests for 
> ftrace and the event tracer, but this blob happened when I first ssh'd 
> into the box.
> 
> In arch/x86/kernel/entry_64.S we have:
> 
> paranoidzeroentry_ist int3 do_int3 DEBUG_STACK
> 
> ..macro paranoidzeroentry sym do_sym
> ENTRY(\sym)
>         INTR_FRAME
>         PARAVIRT_ADJUST_EXCEPTION_FRAME
>         pushq $-1               /* ORIG_RAX: no syscall to restart */
>         CFI_ADJUST_CFA_OFFSET 8
>         subq $15*8, %rsp
>         call save_paranoid
>         TRACE_IRQS_OFF
>         movq %rsp,%rdi          /* pt_regs pointer */
>         xorl %esi,%esi          /* no error code */
>         call \do_sym
>         jmp paranoid_exit       /* %ebx: no swapgs flag */
>         CFI_ENDPROC
> END(\sym)
> ..endm
> 
> 
> ENTRY(paranoid_exit)
>         INTR_FRAME
>         DISABLE_INTERRUPTS(CLBR_NONE)
>         TRACE_IRQS_OFF
>         testl %ebx,%ebx                         /* swapgs needed? */
>         jnz paranoid_restore
>         testl $3,CS(%rsp)
>         jnz   paranoid_userspace
> paranoid_swapgs:
>         TRACE_IRQS_IRETQ 0
>         SWAPGS_UNSAFE_STACK
> paranoid_restore:
>         RESTORE_ALL 8
>         jmp irq_return
> 
> 
> irq_return:
>         INTERRUPT_RETURN
> 
> 
> INTERRUPT_RETURN is simply defined as iretq
> 
> 
> I see that we call TRACE_IRQS_OFF when entering paranoid_exit, but if we 
> do not need to swapgs (we don't because int3 looks like it happened in 
> kernel space) we just call irq_return and jump back. We miss the fact that 
> the irq_return enables interrupts for us.
> 
> I'd try to come up with a fix, but this gets a bit complex, and I figured 
> I let the lockdep irq-tracing guru's play with this magic. I'm just 
> reporting the problem ;-)

Hehe, I think I've started several times at this kprobes stuff, always
makes my head hurt. I'll give it another go.