Messages in this thread Patch in this message | | | From | Arnd Bergmann <> | Subject | show_task() is not SMP safe | Date | Tue, 27 Jan 2004 13:06:37 +0100 |
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Christian Bornträger 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.
In the same function, there is another (harmless) bug that causes the "free stack" indicator to be wrong. It can take any value between zero and the intended meaning unless __alloc_thread_info is modified to clear newly allocated stack memory.
Arnd <><
Index: kernel/sched.c =================================================================== RCS file: /home/cvs/linux-2.5/kernel/sched.c,v retrieving revision 1.56 diff -u -r1.56 sched.c --- kernel/sched.c 24 Nov 2003 09:44:34 -0000 1.56 +++ kernel/sched.c 27 Jan 2004 11:50:55 -0000 @@ -2457,13 +2457,13 @@ 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 @@ -2491,7 +2491,8 @@ else printk(" (NOTLB)\n"); - show_stack(p, NULL); + if (state != TASK_RUNNING) + show_stack(p, NULL); } void show_state(void) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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