Messages in this thread | | | Date | Wed, 17 Nov 2021 06:15:48 -0800 | From | Jakub Kicinski <> | Subject | Re: [syzbot] WARNING: refcount bug in __linkwatch_run_queue |
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On Wed, 17 Nov 2021 09:19:07 +0100 Willy Tarreau wrote: > Thanks for the report. I'm seeing that linkwatch_do_dev() is also > called in linkwatch_forget_dev(), and am wondering if we're not > seeing a sequence like this one: > > linkwatch_forget_dev() > list_del_init() > linkwatch_do_dev() > netdev_state_change() > ... one of the notifiers > ... linkwatch_add_event() => adds to watch list > dev_put() > ... > > __linkwatch_run_queue() > linkwatch_do_dev() > dev_put() > => bang! > > Well, in theory, no, since linkwatch_add_event() will call dev_hold() > when adding to the list, so we ought to leave the first call with a > refcount still covering the list's presence, and I don't see how it > can reach zero before reaching dev_put() in linkwatch_do_dev() as this > function is only called when the event was picked from the list. > > The only difference I'm seeing is that before the patch, a call to > linkwatch_forget_dev() on a non-present device would call dev_put() > without going through dev_activate(), dev_deactivate(), nor > netdev_state_change(), but I'm not seeing how that could make a > difference. linkwatch_forget_dev() is called from netdev_wait_allrefs() > which will wait for the refcnt to be exactly 1, thus even if we queue > an extra event we cant leave that function until the event has been > processed.
The ref leak could come from anywhere, tho. Like:
https://lore.kernel.org/all/87a6i3t2zg.fsf@nvidia.com/
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