On Fri, May 30, 2014 at 06:16:47PM +0200, Peter Zijlstra wrote: > On Fri, May 30, 2014 at 05:50:51PM +0200, Jan Kara wrote: > > > [ 7.492350] ====================================================== > > > [ 7.492350] [ INFO: possible circular locking dependency detected ] > > > [ 7.492350] 3.15.0-rc5-00567-gbafe980 #1 Not tainted > > > [ 7.492350] ------------------------------------------------------- > > > [ 7.492350] swapper/1 is trying to acquire lock: > > > [ 7.492350] (&irq_desc_lock_class){-.-...}, at: [<8107dc8c>] > > > __irq_get_desc_lock+0x3c/0x70 > > > [ 7.492350] > > > [ 7.492350] but task is already holding lock: > > > [ 7.492350] (&port_lock_key){......}, at: [<815f5b27>] > > > serial8250_startup+0x337/0x720 > > > [ 7.492350] > > > [ 7.492350] which lock already depends on the new lock. > > > [ 7.492350] > > > [ 7.492350] > > > [ 7.492350] the existing dependency chain (in reverse order) is: > > > [ 7.492350] > > > -> #2 (&port_lock_key){......}: > > > [ 7.492350] [<810750e5>] lock_acquire+0x85/0x190 > > > [ 7.492350] [<81baed9d>] _raw_spin_lock_irqsave+0x4d/0x60 > > > [ 7.492350] [<8106eb1c>] down_trylock+0xc/0x30 > > > [ 7.492350] [<8107b795>] console_trylock+0x15/0xb0 > > > [ 7.492350] [<8107be8f>] vprintk_emit+0x14f/0x4d0 > > > [ 7.492350] [<81b969b9>] printk+0x38/0x3a > > > [ 7.492350] [<82137f78>] print_ICs+0x5b/0x3e7 > > > [ 7.492350] [<8212bb41>] do_one_initcall+0x8b/0x128 > > > [ 7.492350] [<8212bd7d>] kernel_init_freeable+0x19f/0x236 > > > [ 7.492350] [<81b9238b>] kernel_init+0xb/0xd0 > > > [ 7.492350] [<81bb0080>] ret_from_kernel_thread+0x20/0x30 > > > > But this looks really strange. How can we possibly get port_lock_key in > > down_trylock() which calls raw_spin_lock_irqsave() on console_sem->lock? > > That looks like some strange lockdep key aliasing issue? Peter do you have > > any idea? > > No, strange that, I can't say I've ever seen a bogus stracktrace in > lockdep reports like this. > > So this is through: check_prev_add()->save_trace(). And that doesn't > reuse entries, at worst it can truncate a trace when we run out of > entries, but the above looks complete since it terminates in > lock_acquire(), which is the right place to be. > > But its worse than that, the above trace should link i8259A_lock to > port_lock_key, and I can't see where we would have taken i8259A_lock > either.
Oh, wait, I missed it, that would be: print_ICs()->print_PIC(), it takes that lock there.
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