On Mon, Apr 25, 2022 at 5:13 PM Eric Dumazet <edumazet@xxxxxxxxxx> wrote: > On Mon, Apr 25, 2022 at 8:01 AM Jakub Kicinski <kuba@xxxxxxxxxx> wrote: > > > > On Mon, 25 Apr 2022 16:49:34 +0200 Jann Horn wrote: > > > > Doesn't mean we should make it legal. We can add a warning to catch > > > > abuses. > > > > > > That was the idea with > > > https://lore.kernel.org/netdev/20220128014303.2334568-1-jannh@xxxxxxxxxx/, > > > but I didn't get any replies when I asked what the precise semantics > > > of dev_hold() are supposed to be > > > (https://lore.kernel.org/netdev/CAG48ez1-OyZETvrYAfaHicYW1LbrQUVp=C0EukSWqZrYMej73w@xxxxxxxxxxxxxx/), > > > so I don't know how to proceed... > > > > Yeah, I think after you pointed out that the netdev per cpu refcounting > > is fundamentally broken everybody decided to hit themselves with the > > obliviate spell :S > > dev_hold() has been an increment of a refcount, and dev_put() a decrement. > > Not sure why it is fundamentally broken. Well, it's not quite a refcount. It's a count that can be incremented and decremented but can't be read while the device is alive, and then at some point it turns into a count that can be read and decremented but can't be incremented (see https://lore.kernel.org/netdev/CAG48ez1-OyZETvrYAfaHicYW1LbrQUVp=C0EukSWqZrYMej73w@xxxxxxxxxxxxxx/). Normal refcounts allow anyone who is holding a reference to add another reference. > There are specific steps at device dismantles making sure no more > users can dev_hold() So you're saying it's intentional that even if you're already holding a dev_hold() reference, you may not be allowed to call dev_hold() again?
