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

    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.

    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 ;-)

    -- Steve



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