On (05/03/07 16:25), Greg KH didst pronounce: > 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]> > >
On http://test.kernel.org, elm3b132 is showing a similar error message for the IPS driver on 2.6.21-rc2-mm1. There is no such device in the machine so this is a normal error path for no devices found. The warning looks like BUG: atomic counter underflow at: [<c027ccb4>] kref_put+0x7d/0x9d [<c02a4e38>] bus_remove_driver+0x36/0x41 [<c02a5997>] driver_unregister+0xb/0x13 [<c0286bdd>] pci_unregister_driver+0xb/0x13 [<c04c653a>] ips_module_init+0x41/0x57 [<c04b2bd2>] do_initcalls+0x58/0xf5 [<c01353d5>] register_irq_proc+0x75/0x92 [<c04b2c97>] init+0x0/0x8b [<c04b2ce0>] init+0x49/0x8b [<c01030ff>] kernel_thread_helper+0x7/0x10 This is essentially identical to the warning on ipw2200. It occurs whether the driver is compiled into the kernel or as a module. Reverting Mike's patch fixes the problem - or at least the warning has disappeared. However, I've cc'd the IPS maintainers so they can confirm they are calling pci_unregister_driver() correctly. I note that many drivers in drivers/scsi do not call pci_unregister_driver() in the module_init path. ipw2200 also calls pci_unregister_driver() in the module_init path when an error is encountered. So, maybe this is an error in how the drivers use pci_[un]register_driver() instead of a problem with Mike's patch? > 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 [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
