Spinlock recursion in hvc_poll

From: Jeremy Fitzhardinge
Date: Tue Aug 05 2008 - 14:09:03 EST

Alex Nixon wrote:
Well I say fixed - it just means I can proceed to a spinlock recursion
BUG() 2 secs into the boot process, but it should be easier to track down
with printks and a coherent stack dump at my disposal.
What's the backtrace on this?

I just turned DEBUG_SPINLOCKS back on to try catch this bug again, and it
seems to occur (very roughly) 1/10 of the time, with nothing changing between
runs.

OK, I added some cc:s.

This is definitely a relatively new bug, because I was running with spinlock debugging on all the time a couple of months ago, with no problems.

Backtrace attached.
(Should paste it inline so it gets quoted in replies.)

[ 0.752696] Freeing unused kernel memory: 284k freed
[ 0.772757] BUG: spinlock recursion on CPU#0, swapper/1
[ 0.772782] lock: eaca7000, .magic: dead4ead, .owner: swapper/1, .owner_cpu: 0
[ 0.772814] Pid: 1, comm: swapper Not tainted 2.6.27-rc1 #350
[ 0.772843] [<c021f48d>] spin_bug+0x7c/0x87
[ 0.772878] [<c021f5d5>] _raw_spin_lock+0x35/0xda
[ 0.772904] [<c030c501>] _spin_lock_irqsave+0x3c/0x45
[ 0.772932] [<c027a394>] ? hvc_poll+0x15/0x1ac
[ 0.772964] [<c027a394>] hvc_poll+0x15/0x1ac
OK, I suspect this is a result of Christian Borntraeger's patches to make hvc console cope without interrupts. It's certainly a suggestive set of changes in the right place in the code.

But I have to admit I didn't look at the patches very closely when they went by, so I'm just finger-pointing at the moment. Perhaps it's a pre-existing bug.

J

[ 0.772990] [<c0166b1f>] ? ftrace_record_ip+0x19f/0x1ee
[ 0.773024] [<c027a6a2>] hvc_handle_interrupt+0xf/0x21
[ 0.773051] [<c015f7dc>] handle_IRQ_event+0x1f/0x4f
[ 0.773080] [<c0160d1f>] handle_level_irq+0xc4/0xd1
[ 0.773107] [<c010b3ee>] do_IRQ+0x5c/0x7a
[ 0.773133] [<c0263573>] xen_evtchn_do_upcall+0xad/0x109
[ 0.773164] [<c01096cb>] xen_do_upcall+0x7/0xc
[ 0.773189] [<c0102227>] ? _stext+0x227/0x1000
[ 0.773219] [<c0105be3>] ? xen_force_evtchn_callback+0xf/0x14
[ 0.773253] [<c0106366>] check_events+0x8/0xe
[ 0.773278] [<c0106297>] ? xen_irq_enable_direct_end+0x0/0x1
[ 0.773310] [<c018bc07>] ? cache_alloc_refill+0x251/0x4b4
[ 0.773342] [<c0105be3>] ? xen_force_evtchn_callback+0xf/0x14
[ 0.773375] [<c0106366>] ? check_events+0x8/0xe
[ 0.773405] [<c018bef8>] __kmalloc+0x8e/0xd6
[ 0.773428] [<c010972b>] ? mcount_call+0x5/0xa
[ 0.773457] [<c01c3490>] __proc_create+0x78/0xfb
[ 0.773485] [<c01c380a>] proc_mkdir_mode+0x23/0x48
[ 0.773512] [<c01c3843>] proc_mkdir+0x14/0x16
[ 0.773536] [<c016112e>] register_irq_proc+0x70/0xca
[ 0.773562] [<c0160013>] setup_irq+0x1bc/0x1f2
[ 0.773587] [<c01600d2>] request_irq+0x89/0xa6
[ 0.773614] [<c027a693>] ? hvc_handle_interrupt+0x0/0x21
[ 0.773645] [<c027a681>] notifier_add_irq+0x2f/0x41
[ 0.773670] [<c027a2aa>] hvc_open+0x6f/0xc9
[ 0.773693] [<c027a23b>] ? hvc_open+0x0/0xc9
[ 0.773720] [<c026b436>] tty_open+0x198/0x299
[ 0.773746] [<c0190fbe>] chrdev_open+0x12c/0x143
[ 0.773772] [<c018d170>] __dentry_open+0x113/0x201
[ 0.773797] [<c018d282>] nameidata_to_filp+0x24/0x38
[ 0.773823] [<c0190e92>] ? chrdev_open+0x0/0x143
[ 0.773852] [<c019845d>] do_filp_open+0x351/0x636
[ 0.773878] [<c010972b>] ? mcount_call+0x5/0xa
[ 0.773907] [<c021f5f3>] ? _raw_spin_lock+0x53/0xda
[ 0.773937] [<c021f50c>] ? _raw_spin_unlock+0x74/0x78
[ 0.773967] [<c018cf19>] ? get_unused_fd_flags+0xad/0xb7
[ 0.773997] [<c018cf68>] do_sys_open+0x45/0xbb
[ 0.774022] [<c018d02a>] sys_open+0x23/0x2b
[ 0.774046] [<c0103048>] init_post+0x2a/0xce
[ 0.774070] [<c010967b>] ? kernel_thread_helper+0x7/0x10
[ 0.774101] =======================

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