[PATCH] fix up lockdep trace in fs/exec.c

This fixes the locking error noticed by lockdep:

=============================================
[ INFO: possible recursive locking detected ]
---------------------------------------------
init/1 is trying to acquire lock:
(&sighand->siglock){....}, at: [<c047a78a>] flush_old_exec+0x3ae/0x859

but task is already holding lock:
(&sighand->siglock){....}, at: [<c047a77a>] flush_old_exec+0x39e/0x859

other info that might help us debug this:
2 locks held by init/1:
#0: (tasklist_lock){..--}, at: [<c047a76a>] flush_old_exec+0x38e/0x859
#1: (&sighand->siglock){....}, at: [<c047a77a>] flush_old_exec+0x39e/0x859

stack backtrace:
[<c04051e1>] show_trace_log_lvl+0x54/0xfd
[<c040579d>] show_trace+0xd/0x10
[<c04058b6>] dump_stack+0x19/0x1b
[<c043b33a>] __lock_acquire+0x773/0x997
[<c043bacf>] lock_acquire+0x4b/0x6c
[<c060630b>] _spin_lock+0x19/0x28
[<c047a78a>] flush_old_exec+0x3ae/0x859
[<c0498053>] load_elf_binary+0x4aa/0x1628
[<c0479cab>] search_binary_handler+0xa7/0x24e
[<c047b577>] do_execve+0x15b/0x1f9
[<c04022b4>] sys_execve+0x29/0x4d
[<c0403faf>] syscall_call+0x7/0xb

Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>