Hi, On Thu, 2023-11-23 at 17:32 +0100, Eric Dumazet wrote: > On Thu, Nov 23, 2023 at 3:34 PM Valentin Schneider <vschneid@xxxxxxxxxx> wrote: > > So AFAICT, after we go through the hashdance, there's a reference on > > tw_refcnt held by the tw_timer. > > inet_twsk_deschedule_put() can race with arming the timer, but it only > > calls inet_twsk_kill() if the timer > > was already armed & has been deleted, so there's no risk of calling it > > twice... If I got it right :-) > > Again, I think you missed some details. > > I am OOO for a few days, I do not have time to elaborate. > > You will need to properly track active timer by elevating > tw->tw_refcnt, or I guarantee something wrong will happen. I'm sorry to bring this up again, but I tried to understand what is missing in Valentin's patch and I could not find it. Direct link to the patch, just in case the thread has been lost: https://lore.kernel.org/lkml/20231115210509.481514-2-vschneid@xxxxxxxxxx/ The patch raises the initial tw->tw_refcnt to 4, so it tracks (in advance) the reference for the tw_timer. AFAICS the patch is still prone to the race you mentioned on the RFC: CPU0: allocates a tw, insert it in hash table CPU1: finds the TW and removes it (timer cancel does nothing) CPU0: arms a TW timer, lasting but I understood such race is acceptable. Could you please shed some light? Many thanks, Paolo
