Messages in this thread | | | Date | Wed, 17 Nov 2021 15:20:12 +0100 | From | Willy Tarreau <> | Subject | Re: [syzbot] WARNING: refcount bug in __linkwatch_run_queue |
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On Wed, Nov 17, 2021 at 06:15:48AM -0800, Jakub Kicinski wrote: > 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/
OK thanks for the link, so better wait for this part to clarify itself and see if the issue magically disappears ?
Willy
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