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.
Ok, after a zillion bisects, I've tracked this down to:
commit 63ce18cfe685115ff8d341bae4c9204a79043cf0
Author: Mike Galbraith <[EMAIL PROTECTED]>
Date: Wed Feb 21 12:45:35 2007 -0800
driver core: refcounting fix
Fix a reference counting bug exposed by commit
725522b5453dd680412f2b6463a988e4fd148757. If driver.mod_name
exists, we
take a reference in module_add_driver(), and never release it.
Undo that
reference in module_remove_driver().
Signed-off-by: Mike Galbraith <[EMAIL PROTECTED]>
Cc: Kay Sievers <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Greg Kroah-Hartman <[EMAIL PROTECTED]>
Mike, I've reverted this patch, and I don't see any references leaking.
And, as your patch released the reference on the driver, and the
module_add_driver() call would not grab a reference to the driver, only
the module kobject, I don't see what you were trying to fix with this
patch.
Do you have a test case that this fixes?
Otherwise, I'll just revert it.
thanks,
greg k-h
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