Messages in this thread | | | Subject | Re: [PATCH -rt] Preemption problem in kernel RT Patch | From | Thomas Gleixner <> | Date | Fri, 22 Jun 2007 10:03:51 +0200 |
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Mark,
please fix your mail client to do proper line wraps at column 78.
On Thu, 2007-06-21 at 15:39 -0400, Beauchemin, Mark wrote: > Hi, > I've found a preemption problem in kernel/rtmutex.c:649. The BUG_ON > listed in the patch below makes sure a preemption event hasn't > occurred since the thread last checked the owner of the lock. If it > did happen and the current task is now the owner, it asserts with > BUG_ON. With the RT-PATCH applied, however, interrupts are not > disabled and preemption is possible. The following patch removes the > BUG_ON as it is an incorrect check in the rt kernel. I've checked the > rtmutex code and it appears to handle this case just fine..
Nice, but nevertheless wrong theory.
This check is part of the RT-Patch and it _is_ entirely correct: Something tries to do a spin_lock() on a lock, which the same task has already locked before. That's what the BUG_ON is catching.
There is nothing which can make a task magically the owner of a lock, whether preemption is enabled or not.
> Call Trace: > [D010BB40] [C01C7BA8] rt_spin_lock_slowlock+0x44/0x1f8 (unreliable) > [D010BB90] [C0153464] dev_queue_xmit+0x298/0x2a0 Tunnel2 > [D010BBB0] [C0176398] ip_output+0x288/0x2dc > [D010BBE0] [C01AC078] ipip_tunnel_xmit+0x508/0x698 > [D010BC60] [C0150DF4] dev_hard_start_xmit+0x1b4/0x2a4 > [D010BC80] [C0153430] dev_queue_xmit+0x264/0x2a0 Tunnel4 > [D010BCA0] [C0176398] ip_output+0x288/0x2dc > [D010BCD0] [C01AC078] ipip_tunnel_xmit+0x508/0x698 > [D010BD50] [C0150DF4] dev_hard_start_xmit+0x1b4/0x2a4 > [D010BD70] [C0153430] dev_queue_xmit+0x264/0x2a0 Tunnel2 > [D010BD90] [C0176398] ip_output+0x288/0x2dc > [D010BDC0] [C017685C] ip_queue_xmit+0x1ac/0x4e4 > [D010BE30] [C018762C] tcp_transmit_skb+0x390/0x810 > [D010BE70] [C018882C] tcp_retransmit_skb+0x160/0x638 > [D010BEA0] [C018BA5C] tcp_write_timer+0x274/0x6c0 > [D010BED0] [C0024314] run_timer_softirq+0x2d0/0xedc > [D010BF80] [C001F1C4] ksoftirqd+0xf8/0x1b0 > [D010BFC0] [C0031588] kthread+0xc0/0xfc > [D010BFF0] [C000471C] kernel_thread+0x44/0x60
Looks like the tunnel code is doing a nasty recursive thing.
Dave, any idea ?
Mark, can you please turn on CONFIG_PROVE_LOCKING. This should produce more detailed information about the problem.
tglx
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