From: Arnd Bergmann <arnd@arndb.de>
Christian Borntr�ger noticed that the kernel can crash after <SysRq>-T. It
appears that the show_task function gets called for all tasks, which does
not work if one of the tasks is running in a system call on another CPU.
In that case the result of thread_saved_pc and show_stack is undefined and
likely to cause a crash.
For tasks running in user space on other CPUs, show_task() is probably
harmless, but I'm not sure if that's true on all architectures.
The patch below is still racy for tasks that are about to sleep, but it
demonstrates the problem.
---
25-akpm/kernel/sched.c | 11 ++++++-----
1 files changed, 6 insertions(+), 5 deletions(-)
diff -puN kernel/sched.c~show_task-fix kernel/sched.c
--- 25/kernel/sched.c~show_task-fix Wed Feb 11 18:37:12 2004
+++ 25-akpm/kernel/sched.c Wed Feb 11 18:37:12 2004
@@ -2917,13 +2917,13 @@ static void show_task(task_t * p)
else
printk("?");
#if (BITS_PER_LONG == 32)
- if (p == current)
- printk(" current ");
+ if (state == TASK_RUNNING)
+ printk(" running ");
else
printk(" %08lX ", thread_saved_pc(p));
#else
- if (p == current)
- printk(" current task ");
+ if (state == TASK_RUNNING)
+ printk(" running task ");
else
printk(" %016lx ", thread_saved_pc(p));
#endif
@@ -2945,7 +2945,8 @@ static void show_task(task_t * p)
else
printk(" (NOTLB)\n");
- show_stack(p, NULL);
+ if (state != TASK_RUNNING)
+ show_stack(p, NULL);
}
void show_state(void)
_