Re: kref refcounting breakage in mainline

From: Greg KH
Date: Sat Mar 03 2007 - 00:49:31 EST


On Fri, Mar 02, 2007 at 12:58:33AM -0800, Andrew Morton wrote:
>
> -mm has a debugging patch which warns when atomic_dec_and_test() takes an
> atomic_t negative
> (ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.20/2.6.20-mm2/broken-out/detect-atomic-counter-underflows.patch).
>
>
> When it is applied to current mainline, a simple `rmmod ipw2200' gives:
>
> [ 75.825072] BUG: atomic counter underflow at:
> [ 75.825180] [<c01c6eb4>] kref_put+0x66/0x82
> [ 75.825278] [<c022e4d4>] bus_remove_driver+0x66/0x75
> [ 75.825383] [<c022ee2c>] driver_unregister+0x8/0x13
> [ 75.825484] [<c01d7add>] pci_unregister_driver+0xc/0x45
> [ 75.825593] [<c0132147>] sys_delete_module+0x157/0x17c
> [ 75.825703] [<c013c663>] audit_syscall_entry+0x10d/0x137
> [ 75.825818] [<c0103b14>] syscall_call+0x7/0xb
> [ 75.825913] [<c02d0000>] xfrm4_dst_destroy+0xe/0xd5
>
> This didn't happen in 2.6.20-mm2, so this bug was introduced by a patch
> which was not in the -mm lineup twelve days ago.
>
> Presumably the effect of this is a memory leak or a use-after-free.

Ugh.

I'll add it to my local tree here and try to bisect to find the problem.

thanks for the pointer,

greg k-h
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