Re: kref refcounting breakage in mainline

[Greg KH <greg@kroah.com>]

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