> [ 55.630000] [<c0274e74>] (_spin_lock_irqsave+0x44/0x58) from [<c019d608>] (gs_write_room+0x10/0x58) > [ 55.630000] [<c019d608>] (gs_write_room+0x10/0x58) from [<c0156058>] (tty_write_room+0x20/0x28) > [ 55.630000] [<c0156058>] (tty_write_room+0x20/0x28) from [<c01538e0>] (process_echoes+0x4c/0x288) > [ 55.630000] [<c01538e0>] (process_echoes+0x4c/0x288) from [<c0155a40>] (n_tty_receive_buf+0x9ec/0xecc) > [ 55.630000] [<c0155a40>] (n_tty_receive_buf+0x9ec/0xecc) from [<c0158174>] (flush_to_ldisc+0x104/0x1b0) > [ 55.630000] [<c0158174>] (flush_to_ldisc+0x104/0x1b0) from [<c00498e0>] (worker_thread+0x1d0/0x2cc) > [ 55.630000] [<c00498e0>] (worker_thread+0x1d0/0x2cc) from [<c004d55c>] (kthread+0x58/0x90) > [ 55.630000] [<c004d55c>] (kthread+0x58/0x90) from [<c003c03c>] (do_exit+0x0/0x5d0) > [ 55.630000] [<c003c03c>] (do_exit+0x0/0x5d0) from [<c6c26180>] (0xc6c26180) > [ 55.630000] Code: ea000076 e59d100c e3510000 1a000002 (e5994004) > [ 55.640000] ---[ end trace f9a4499d9482c504 ]--- > [ 55.650000] note: events/0[5] exited with preempt_count 1 > > The low latency mode is disabled. I've tested different ways of gathering > the debug output from my lowlevel udc driver: in first attempt it was > printk(KERN_INFO ...) then I switched to use lowlevel printascii() to remove > possible interaction with console/tty framework at all. In both cases I got > the above NULL pointer exception. It only worked fine when I switched to > printk(KERN_DEBUG ...) with debug level above KERN_DEBUG, so all the > messages were only buffered in dmesg buffer. This looks like a timing issue > in tty framework... Looks to me like the gs_write_room function takes a lock already held when the driver calls tty_flip_buffer_push() - which will and can call back into the driver (eg for echo processing) -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
