I just managed to create this infamous bug pattern once again:
function()
{
stall_topmost_domain();
...
if (condition)
return;
...
unstall_topmost_domain();
}
The result is often a locked-up system, specifically the root domain no
longer receives IRQs. Unless you find the bug quickly by code
inspection, debugging/instrumenting can take quite some time.
To catch such issues earlier, I therefore propose the following
extension of ipipe_check_context. It is based on the assumption that the
topmost domain should never be stalled when lower domains execute that
check. This specifically takes care of not breaking Xenomai's IRQ shield
(a mid-prio domain that intentionally blocks Linux IRQs).
This is how this patch sees my bug:
I-pipe: Detected stalled topmost domain, probably caused by a bug.
A critical section may have been left unterminated.
Pid: 4483, comm: cyclictest Tainted: G W 2.6.26.2-xeno_64 #55
Call Trace:
[<ffffffff8026b61b>] ipipe_check_context+0x11e/0x128
[<ffffffff80474849>] down_write+0x1d/0x2e
[<ffffffff802c9686>] ipipe_disable_ondemand_mappings+0x41/0x3b3
[<ffffffff8021ed3c>] ? mcount+0x4c/0x72
[<ffffffff80283b93>] xnshadow_map+0x65/0x2a6
[<ffffffff8021ed3c>] ? mcount+0x4c/0x72
[<ffffffff802b5bc5>] __pthread_setschedparam+0xd3/0x3b9
[<ffffffff80283840>] losyscall_event+0x11f/0x1ee
[<ffffffff80283721>] ? losyscall_event+0x0/0x1ee
[<ffffffff8026c6ad>] __ipipe_dispatch_event+0x127/0x255
[<ffffffff8021e922>] __ipipe_syscall_root+0xa2/0x194
[<ffffffff8047555a>] __ipipe_syscall_root_thunk+0x35/0x6a
[<ffffffff8020c034>] ? system_call_after_swapgs+0x54/0x94
I-pipe tracer log (100 points):
| *+func 0 ipipe_trace_panic_freeze+0xe
(ipipe_check_context+0xab)
| *+func 0 find_next_bit+0x9 (__next_cpu+0x1e)
| *+func 0 __next_cpu+0x9 (ipipe_check_context+0x9f)
| *+func -1 find_first_bit+0x9 (__first_cpu+0x13)
| *+func -1 __first_cpu+0x9 (ipipe_check_context+0x79)
| *+func -1 ipipe_check_context+0xc (down_write+0x1d)
| *+func -1 down_write+0xe
(ipipe_disable_ondemand_mappings+0x41)
| *+func -2 _spin_lock+0x9 (get_task_mm+0x1d)
| *+func -2 get_task_mm+0xe
(ipipe_disable_ondemand_mappings+0x1e)
| *+func -3 ipipe_disable_ondemand_mappings+0x16
(xnshadow_map+0x65)
| *+func -3 xnshadow_map+0x12 (__pthread_setschedparam+0xd3)
| *+func -4 xnsynch_init+0x9 (xnregistry_enter+0xf8)
| +begin 0x80000000 -5 xnregistry_enter+0x5b (pthread_create+0x321)
+func -5 strchr+0x9 (xnregistry_enter+0x40)
+func -6 xnregistry_enter+0x16 (pthread_create+0x321)
| +end 0x80000000 -6 __ipipe_restore_pipeline_head+0xea
(pthread_create+0x309)
| *+func -6 __ipipe_restore_pipeline_head+0xe
(pthread_create+0x309)
| *+func -7 ppd_lookup_inner+0xe (xnshadow_ppd_get+0x5d)
| *+func -8 xnshadow_ppd_get+0xd (pthread_create+0x28c)
| +begin 0x80000000 -8 pthread_create+0x227
(__pthread_setschedparam+0xb6)
(xnregistry_enter is left with nklock still held. Fix committed.)
Jan
---
kernel/ipipe/core.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
Index: b/kernel/ipipe/core.c
===================================================================
--- a/kernel/ipipe/core.c
+++ b/kernel/ipipe/core.c
@@ -1567,7 +1567,9 @@ void ipipe_check_context(struct ipipe_do
/* Note: We don't make the per_cpu access atomic. We assume that code
which temporarily disables the check does this in atomic context
only. */
- if (likely(ipipe_current_domain->priority <= border_ipd->priority) ||
+ if (likely(ipipe_current_domain->priority <= border_ipd->priority &&
+ !test_bit(IPIPE_STALL_FLAG,
+ &ipipe_head_cpudom_var(status))) ||
!per_cpu(ipipe_percpu_context_check, ipipe_processor_id()))
return;
@@ -1575,10 +1577,18 @@ void ipipe_check_context(struct ipipe_do
ipipe_trace_panic_freeze();
ipipe_set_printk_sync(ipipe_current_domain);
- printk(KERN_ERR "I-pipe: Detected illicit call from domain '%s'\n"
- KERN_ERR " into a service reserved for domain '%s' and "
- "below.\n",
- ipipe_current_domain->name, border_ipd->name);
+
+ if (ipipe_current_domain->priority > border_ipd->priority)
+ printk(KERN_ERR "I-pipe: Detected illicit call from domain "
+ "'%s'\n"
+ KERN_ERR " into a service reserved for domain "
+ "'%s' and below.\n",
+ ipipe_current_domain->name, border_ipd->name);
+ else
+ printk(KERN_ERR "I-pipe: Detected stalled topmost domain, "
+ "probably caused by a bug.\n"
+ " A critical section may have been "
+ "left unterminated.\n");
dump_stack();
ipipe_trace_panic_dump();
}
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