Re: [uml-devel] 2.6.25 uml kernel crashes when it calls down() on a semaphore with zero counter

[Jeff Dike <jdike@addtoit.com>]

On Mon, Jul 14, 2008 at 05:06:49PM +0800, Jiaying Zhang wrote:
> The 2.6.24 kernels are OK, but I have seen this problem with all of the
> 2.6.25 kernels I have tried. There have been a lot of changes between
> 2.6.24 kernels and 2.6.25 kernels. I am not sure which one may lead
> to this problem.

So bisect it.

> Looks like the problem happens when __down_interruptible is called.
> I checked the semaphore passed to __down_interruptible under gdb
> and found it was corrupted:
> (gdb) f 18
> #18 __down_interruptible (sem=0x9f68d08) at include/linux/list.h:50
> 50              prev->next = new;
> (gdb) p sem
> $15 = (struct semaphore *) 0x9f68d08
> (gdb) p *sem
> $16 = {count = {counter = -268435295}, sleepers = 4, wait = {lock =
> {raw_lock = {<No data fields>}}, task_list = {
>       next = 0x9f68d5c, prev = 0x18124}}}
> 
> But the semaphore looks correct before calling down_interruptible:

What's the problem with debugging this, then?  You step through the
code starting when the semaphore is good and see exactly when it gets
corrupted.

				Jeff

-- 
Work email - jdike at linux dot intel dot com

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