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Jakub Kicinski says: ==================== net: fix issues around register_netdevice() failures This series attempts to clean up the life cycle of struct net_device. Dave has added dev->needs_free_netdev in the past to fix double frees, we can lean on that mechanism a little more to fix remaining issues with register_netdevice(). This is the next chapter of the saga which already includes: commit0e0eee2465("net: correct error path in rtnl_newlink()") commite51fb15231("rtnetlink: fix a memory leak when ->newlink fails") commitcf124db566("net: Fix inconsistent teardown and release of private netdev state.") commit93ee31f14f("[NET]: Fix free_netdev on register_netdev failure.") commit814152a89e("net: fix memleak in register_netdevice()") commit10cc514f45("net: Fix null de-reference of device refcount") The immediate problem which gets fixed here is that calling free_netdev() right after unregister_netdevice() is illegal because we need to release rtnl_lock first, to let the unregistration finish. Note that unregister_netdevice() is just a wrapper of unregister_netdevice_queue(), it only does half of the job. Where this limitation becomes most problematic is in failure modes of register_netdevice(). There is a notifier call right at the end of it, which lets other subsystems veto the entire thing. At which point we should really go through a full unregister_netdevice(), but we can't because callers may go straight to free_netdev() after the failure, and that's no bueno (see the previous paragraph). This set makes free_netdev() more lenient, when device is still being unregistered free_netdev() will simply set dev->needs_free_netdev and let the unregister process do the freeing. With the free_netdev() problem out of the way failures in register_netdevice() can make use of net_todo, again. Users are still expected to call free_netdev() right after failure but that will only set dev->needs_free_netdev. To prevent the pathological case of: dev->needs_free_netdev = true; if (register_netdevice(dev)) { rtnl_unlock(); free_netdev(dev); } make register_netdevice()'s failure clear dev->needs_free_netdev. Problems described above are only present with register_netdevice() / unregister_netdevice(). We have two parallel APIs for registration of devices: - those called outside rtnl_lock (register_netdev(), and unregister_netdev()); - and those to be used under rtnl_lock - register_netdevice() and unregister_netdevice(). The former is trivial and has no problems. The alternative approach to fix the latter would be to also separate the freeing functions - i.e. add free_netdevice(). This has been implemented (incl. converting all relevant calls in the tree) but it feels a little unnecessary to put the burden of choosing the right free_netdev{,ice}() call on the programmer when we can "just do the right thing" by default. ==================== Link: https://lore.kernel.org/r/20210106184007.1821480-1-kuba@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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