Messages in this thread | | | Date | Fri, 17 Apr 2009 00:16:39 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 2/2] tracing/events/lockdep: move tracepoints within recursive protection |
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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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