lockdep: fix ftrace irq tracing false positive
fix this false positive:
[ 0.020000] ------------[ cut here ]------------
[ 0.020000] WARNING: at kernel/lockdep.c:2718 check_flags+0x14a/0x170()
[ 0.020000] Modules linked in:
[ 0.020000] Pid: 0, comm: swapper Not tainted
2.6.26-tip-00343-gd7e5521-dirty #14486
[ 0.020000] [<
c01312e4>] warn_on_slowpath+0x54/0x80
[ 0.020000] [<
c067e451>] ? _spin_unlock_irqrestore+0x61/0x70
[ 0.020000] [<
c0131bb1>] ? release_console_sem+0x201/0x210
[ 0.020000] [<
c0143d65>] ? __kernel_text_address+0x35/0x40
[ 0.020000] [<
c010562e>] ? dump_trace+0x5e/0x140
[ 0.020000] [<
c01518b5>] ? __lock_acquire+0x245/0x820
[ 0.020000] [<
c015063a>] check_flags+0x14a/0x170
[ 0.020000] [<
c0151ed8>] ? lock_acquire+0x48/0xc0
[ 0.020000] [<
c0151ee1>] lock_acquire+0x51/0xc0
[ 0.020000] [<
c014a16c>] ? down+0x2c/0x40
[ 0.020000] [<
c010a609>] ? sched_clock+0x9/0x10
[ 0.020000] [<
c067e7b2>] _write_lock+0x32/0x60
[ 0.020000] [<
c013797f>] ? request_resource+0x1f/0xb0
[ 0.020000] [<
c013797f>] request_resource+0x1f/0xb0
[ 0.020000] [<
c02f89ad>] vgacon_startup+0x2bd/0x3e0
[ 0.020000] [<
c094d62a>] con_init+0x19/0x22f
[ 0.020000] [<
c0330c7c>] ? tty_register_ldisc+0x5c/0x70
[ 0.020000] [<
c094cf49>] console_init+0x20/0x2e
[ 0.020000] [<
c092a969>] start_kernel+0x20c/0x379
[ 0.020000] [<
c092a516>] ? unknown_bootoption+0x0/0x1f6
[ 0.020000] [<
c092a099>] __init_begin+0x99/0xa1
[ 0.020000] =======================
[ 0.020000] ---[ end trace
4eaa2a86a8e2da22 ]---
[ 0.020000] possible reason: unannotated irqs-on.
[ 0.020000] irq event stamp: 0
which occurs if CONFIG_TRACE_IRQFLAGS=y, CONFIG_DEBUG_LOCKDEP=y,
but CONFIG_PROVE_LOCKING is disabled.
Signed-off-by: Ingo Molnar <mingo@elte.hu>