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    SubjectRe: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection
    * Steven Rostedt (rostedt@goodmis.org) 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?
    >

    Not in your ftrace tree. My LTTng tree includes the immediate values,
    which brienfly uses the int3 handler when enabling/disabling
    tracepoints. But this seems unrelated to your problem.

    > I have kprobes defined but not any kprobe self tests on.
    >

    Could this be a userspace breakpoint then ?

    > 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.

    Also note that maybe some entry.S annotation could be missing, making
    kallsyms think it was running within int3 when in fact it was running in
    a different function. I would double-check with objdump givin the
    ffffffff80610c76 address to make sure.

    Just giving my 2 cents before going to bed. I don't have any more brain
    left for tonight.

    Cheers,

    Mathieu

    >
    > 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 ;-)
    >
    > -- Steve
    >

    --
    Mathieu Desnoyers
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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