Messages in this thread Patch in this message | | | Date | Fri, 31 Aug 2007 00:28:58 -0500 | From | Eric Sandeen <> | Subject | [RFC][PATCH] detect & print stack overruns at oops time |
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In thinking about the 4KSTACKS + STACKOVERFLOW problems, I thought about this - if an oops occurs, explicitly print whether the current esp is now overrunning the stack, whether the thread has ever overrun the stack, else print the max stack excursion for the oopsing thread, if DEBUG_STACK_USAGE is enabled.
1) maybe printing the info for a non-blown stack is not useful.. 2) current esp past end of stack can already be deduced, but this makes it more plain... 3) if the initialization of end_of_stack is problematic for any reason, it could be removed and the "did we ever overrun" test could be moved under the DEBUG_STACK_USAGE ifdef
Thoughts? This is a separate problem from the piggy dump_stack() path, but it seems to me it might be useful in looking at stack-related oopses when they do occur. With this change, it seems feasible to turn off DEBUG_STACKOVERFLOW, turn on DEBUG_STACK_USAGE, and just get the bad news when it's actually happened. :)
Thanks, -Eric
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Index: linux-2.6.22-rc4/arch/i386/mm/fault.c =================================================================== --- linux-2.6.22-rc4.orig/arch/i386/mm/fault.c +++ linux-2.6.22-rc4/arch/i386/mm/fault.c @@ -525,6 +525,8 @@ no_context: if (oops_may_print()) { __typeof__(pte_val(__pte(0))) page; + unsigned long *stackend = end_of_stack(tsk); + int overrun; #ifdef CONFIG_X86_PAE if (error_code & 16) { @@ -543,6 +545,27 @@ no_context: printk(KERN_ALERT "BUG: unable to handle kernel paging" " request"); printk(" at virtual address %08lx\n",address); + + overrun = (unsigned long)stackend - (unsigned long)(®s->esp); + if (overrun > 0) { + printk(KERN_ALERT "Thread overrunning stack by %d " + "bytes\n", overrun); + } else { +#ifdef CONFIG_DEBUG_STACK_USAGE + int free; + unsigned long *n = stackend; + while (!*n) + n++; + free = (unsigned long)n - (unsigned long)stackend; + if (free) + printk(KERN_ALERT "Thread used within %d bytes" + " of stack end\n", free); +#endif + /* won't catch 100% - stack may have 0s here by chance */ + if (*stackend) /* was init'd to 0 */ + printk(KERN_ALERT "Thread overran the stack?\n"); + } + printk(KERN_ALERT " printing eip:\n"); printk("%08lx\n", regs->eip); Index: linux-2.6.22-rc4/kernel/fork.c =================================================================== --- linux-2.6.22-rc4.orig/kernel/fork.c +++ linux-2.6.22-rc4/kernel/fork.c @@ -163,6 +163,7 @@ static struct task_struct *dup_task_stru { struct task_struct *tsk; struct thread_info *ti; + unsigned long *stackend; prepare_to_copy(orig); @@ -179,6 +180,8 @@ static struct task_struct *dup_task_stru *tsk = *orig; tsk->stack = ti; setup_thread_stack(tsk, orig); + stackend = end_of_stack(tsk); + *stackend = 0; /* for overflow detection */ #ifdef CONFIG_CC_STACKPROTECTOR tsk->stack_canary = get_random_int(); - 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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