Small patch, fairly useful effect (IMHO): This introduces
ipipe_check_context(border_ipd), a test if the caller is running in
domain border_ipd or below. If not, a warning + stack trace is issued on
the kernel console.
The background is that functions of lower-priority domains that are not
protected against preemptions by higher domains must not be invoked by
the latter. Example: wakeup of a Linux process from a Xenomai interrupt
handler (fairly tempting for RTDM driver developers, I know).
As an application of this generic check, preempt_disable() and
might_resched() of the Linux kernel are instrumented with
ipipe_check_context(&ipipe_root). This catches all spin_lock invocations
as well as mutexes, (rw-)semaphores and other sleeping Linux services.
Example:
#include <linux/module.h>
#include <linux/wait.h>
#include <rtdm/rtdm_driver.h>
rtdm_task_t task;
static DECLARE_WAIT_QUEUE_HEAD(waitqueue);
void task_fnc(void *arg)
{
rtdm_printk("about to do something illegal...\n");
wake_up(&waitqueue);
rtdm_printk("done\n");
}
int ipipe_debug_test(void)
{
rtdm_task_init(&task, "ipipe_debug_test", task_fnc, NULL, 20, 0);
rtdm_task_join_nrt(&task, 100);
return -ENOANO;
}
module_init(ipipe_debug_test);
Loading this module will give
> I-pipe: Detected illicit call from domain 'Xenomai'
> into a service reserved for domain 'Linux' and below.
> c499f390 00000000 00000000 00000003 c499f3b4 c0102bc9 c0271903
> ffffffff
> 00000001 c499f3c8 c012b5e3 c0275577 c0275c4c c02800bd c499f3e0
> c010bf98
> c49953fc c04e9d60 c4995680 c499588c c499f3f0 c4995078 00000000
> c4995099
> Call Trace:
> <c0102b9e> show_stack_log_lvl+0x85/0x8f <c0102bc9> show_stack+0x21/0x29
> <c012b5e3> ipipe_check_context+0x58/0x5d <c010bf98> __wake_up+0x24/0x52
> <c4995078> task_fnc+0x23/0x33 [rtdm_buggy_linux_call] <c01313d5>
> xnarch_thread_redirect+0x1d/0x27
> <00000000> _stext+0x3feffdc0/0x3c
This patch is an RFC as the following issues need to be resolved:
o The might be parts of I-pipe remaining that make use of
preemp_disable even over non-root contexts. Philippe indicated the
PPC PIC code would be one example.
o We need a common header with only elementary dependencies to avoid
duplications like in preempt.h and kernel.h. This would also address
the problem of my earlier posted inline-root-stalling patch.
o It has to be decided if this patch shall be part of the base patch or
the tracer add-on (maybe renamed as ipipe-debugging).
Jan
---
arch/i386/kernel/ipipe-root.c | 9 ++++++---
include/linux/ipipe.h | 6 ++++++
include/linux/kernel.h | 16 ++++++++++++++--
include/linux/preempt.h | 11 ++++++++++-
kernel/ipipe/Kconfig.debug | 9 +++++++++
kernel/ipipe/generic.c | 31 +++++++++++++++++++++++++++++++
6 files changed, 76 insertions(+), 6 deletions(-)
Index: linux-2.6.17.13/include/linux/ipipe.h
===================================================================
--- linux-2.6.17.13.orig/include/linux/ipipe.h
+++ linux-2.6.17.13/include/linux/ipipe.h
@@ -694,6 +694,12 @@ int fastcall ipipe_set_ptd(int key,
void fastcall *ipipe_get_ptd(int key);
+#ifdef CONFIG_IPIPE_DEBUG_CONTEXT
+void fastcall ipipe_check_context(struct ipipe_domain *border_ipd);
+#else /* !CONFIG_IPIPE_DEBUG_CONTEXT */
+#define ipipe_check_context(border_ipd) do { } while (0)
+#endif /* CONFIG_IPIPE_DEBUG_CONTEXT */
+
#define local_irq_enable_hw_cond() local_irq_enable_hw()
#define local_irq_disable_hw_cond() local_irq_disable_hw()
#define local_irq_save_hw_cond(flags) local_irq_save_hw(flags)
Index: linux-2.6.17.13/kernel/ipipe/Kconfig.debug
===================================================================
--- linux-2.6.17.13.orig/kernel/ipipe/Kconfig.debug
+++ linux-2.6.17.13/kernel/ipipe/Kconfig.debug
@@ -2,6 +2,15 @@ config IPIPE_DEBUG
bool "I-pipe debugging"
depends on IPIPE
+config IPIPE_DEBUG_CONTEXT
+ bool "Check for illicit cross-domain calls"
+ depends on IPIPE_DEBUG
+ ---help---
+ Enable this feature to arm checkpoints in the kernel that
+ verify the correct invocation context. On entry of critical
+ Linux services a warning is issued if the caller is not
+ running over the root domain.
+
config IPIPE_TRACE
bool "Latency tracing"
depends on IPIPE_DEBUG
Index: linux-2.6.17.13/kernel/ipipe/generic.c
===================================================================
--- linux-2.6.17.13.orig/kernel/ipipe/generic.c
+++ linux-2.6.17.13/kernel/ipipe/generic.c
@@ -29,6 +29,9 @@
#ifdef CONFIG_PROC_FS
#include <linux/proc_fs.h>
#endif /* CONFIG_PROC_FS */
+#ifdef CONFIG_IPIPE_TRACE_MCOUNT
+#include <linux/ipipe_trace.h>
+#endif /* CONFIG_IPIPE_TRACE_MCOUNT */
MODULE_DESCRIPTION("I-pipe");
MODULE_LICENSE("GPL");
@@ -410,6 +413,34 @@ void fastcall *ipipe_get_ptd (int key)
return current->ptd[key];
}
+#ifdef CONFIG_IPIPE_DEBUG_CONTEXT
+void fastcall ipipe_check_context(struct ipipe_domain *border_ipd)
+{
+ static int check_hit;
+
+ if (likely(ipipe_current_domain->priority <= border_ipd->priority) ||
+ check_hit)
+ return;
+
+ check_hit = 1;
+
+#ifdef CONFIG_IPIPE_TRACE_MCOUNT
+ ipipe_trace_panic_freeze();
+#endif /* CONFIG_IPIPE_TRACE_MCOUNT */
+ ipipe_set_printk_sync(ipipe_current_domain);
+ printk(KERN_ERR "I-pipe: Detected illicit call from domain '%s'\n"
+ " into a service reserved for domain '%s' and below.\n",
+ ipipe_current_domain->name, border_ipd->name);
+#ifdef CONFIG_IPIPE_TRACE_MCOUNT
+ ipipe_trace_panic_dump();
+#else /* !CONFIG_IPIPE_TRACE_MCOUNT */
+ show_stack(NULL, NULL);
+#endif /* CONFIG_IPIPE_TRACE_MCOUNT */
+}
+
+EXPORT_SYMBOL(ipipe_check_context);
+#endif /* CONFIG_IPIPE_DEBUG_CONTEXT */
+
EXPORT_SYMBOL(ipipe_register_domain);
EXPORT_SYMBOL(ipipe_unregister_domain);
EXPORT_SYMBOL(ipipe_free_virq);
Index: linux-2.6.17.13/include/linux/kernel.h
===================================================================
--- linux-2.6.17.13.orig/include/linux/kernel.h
+++ linux-2.6.17.13/include/linux/kernel.h
@@ -60,11 +60,23 @@ struct user;
* be biten later when the calling function happens to sleep when it is not
* supposed to.
*/
+
+/* FIXME: This is ugly... */
+extern struct ipipe_domain ipipe_root;
+#ifdef CONFIG_IPIPE_DEBUG_CONTEXT
+void fastcall ipipe_check_context(struct ipipe_domain *border_ipd);
+#else /* !CONFIG_IPIPE_DEBUG_CONTEXT */
+#define ipipe_check_context(border_ipd) do { } while (0)
+#endif /* CONFIG_IPIPE_DEBUG_CONTEXT */
+
#ifdef CONFIG_PREEMPT_VOLUNTARY
extern int cond_resched(void);
-# define might_resched() cond_resched()
+# define might_resched() do { \
+ ipipe_check_context(&ipipe_root); \
+ cond_resched(); \
+ } while (0)
#else
-# define might_resched() do { } while (0)
+# define might_resched() ipipe_check_context(&ipipe_root)
#endif
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
Index: linux-2.6.17.13/include/linux/preempt.h
===================================================================
--- linux-2.6.17.13.orig/include/linux/preempt.h
+++ linux-2.6.17.13/include/linux/preempt.h
@@ -23,6 +23,14 @@
#define preempt_count() (current_thread_info()->preempt_count)
+/* FIXME: This is ugly... */
+extern struct ipipe_domain ipipe_root;
+#ifdef CONFIG_IPIPE_DEBUG_CONTEXT
+void fastcall ipipe_check_context(struct ipipe_domain *border_ipd);
+#else /* !CONFIG_IPIPE_DEBUG_CONTEXT */
+#define ipipe_check_context(border_ipd) do { } while (0)
+#endif /* CONFIG_IPIPE_DEBUG_CONTEXT */
+
#ifdef CONFIG_PREEMPT
asmlinkage void preempt_schedule(void);
@@ -38,6 +46,7 @@ extern struct ipipe_domain ipipe_root;
#define preempt_disable() \
do { \
+ ipipe_check_context(&ipipe_root); \
if (ipipe_preempt_guard()) { \
inc_preempt_count(); \
barrier(); \
@@ -69,7 +78,7 @@ do {
\
#else
-#define preempt_disable() do { } while (0)
+#define preempt_disable() ipipe_check_context(&ipipe_root)
#define preempt_enable_no_resched() do { } while (0)
#define preempt_enable() do { } while (0)
#define preempt_check_resched() do { } while (0)
Index: linux-2.6.17.13/arch/i386/kernel/ipipe-root.c
===================================================================
--- linux-2.6.17.13.orig/arch/i386/kernel/ipipe-root.c
+++ linux-2.6.17.13/arch/i386/kernel/ipipe-root.c
@@ -70,9 +70,12 @@ static int __ipipe_ack_common_irq(unsign
ipipe_load_cpuid(); /* hw interrupts are off. */
flags = ipipe_test_and_stall_pipeline();
- preempt_disable();
- desc->handler->ack(irq);
- preempt_enable_no_resched();
+ if (ipipe_percpu_domain[cpuid] == ipipe_root_domain) {
+ preempt_disable();
+ desc->handler->ack(irq);
+ preempt_enable_no_resched();
+ } else
+ desc->handler->ack(irq);
ipipe_restore_pipeline_nosync(ipipe_percpu_domain[cpuid], flags, cpuid);
return 1;
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