Messages in this thread | | | Date | Mon, 5 Mar 2007 16:25:21 -0800 | From | Greg KH <> | Subject | Re: kref refcounting breakage in mainline |
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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 <efault@gmx.de> 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 <efault@gmx.de> Cc: Kay Sievers <kay.sievers@vrfy.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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 - 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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