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Date: Mon, 31 Oct 2022 23:03:09 +0100 From: Jakub Sitnicki <jakub@...udflare.com> To: Cong Wang <xiyou.wangcong@...il.com> Cc: Cong Wang <cong.wang@...edance.com>, sdf@...gle.com, netdev@...r.kernel.org, bpf@...r.kernel.org, John Fastabend <john.fastabend@...il.com> Subject: Re: [Patch bpf] sock_map: convert cancel_work_sync() to cancel_work() On Fri, Oct 28, 2022 at 12:16 PM -07, Cong Wang wrote: > On Mon, Oct 24, 2022 at 03:33:13PM +0200, Jakub Sitnicki wrote: >> On Tue, Oct 18, 2022 at 11:13 AM -07, sdf@...gle.com wrote: >> > On 10/17, Cong Wang wrote: >> >> From: Cong Wang <cong.wang@...edance.com> >> > >> >> Technically we don't need lock the sock in the psock work, but we >> >> need to prevent this work running in parallel with sock_map_close(). >> > >> >> With this, we no longer need to wait for the psock->work synchronously, >> >> because when we reach here, either this work is still pending, or >> >> blocking on the lock_sock(), or it is completed. We only need to cancel >> >> the first case asynchronously, and we need to bail out the second case >> >> quickly by checking SK_PSOCK_TX_ENABLED bit. >> > >> >> Fixes: 799aa7f98d53 ("skmsg: Avoid lock_sock() in sk_psock_backlog()") >> >> Reported-by: Stanislav Fomichev <sdf@...gle.com> >> >> Cc: John Fastabend <john.fastabend@...il.com> >> >> Cc: Jakub Sitnicki <jakub@...udflare.com> >> >> Signed-off-by: Cong Wang <cong.wang@...edance.com> >> > >> > This seems to remove the splat for me: >> > >> > Tested-by: Stanislav Fomichev <sdf@...gle.com> >> > >> > The patch looks good, but I'll leave the review to Jakub/John. >> >> I can't poke any holes in it either. >> >> However, it is harder for me to follow than the initial idea [1]. >> So I'm wondering if there was anything wrong with it? > > It caused a warning in sk_stream_kill_queues() when I actually tested > it (after posting). We must have seen the same warnings. They seemed unrelated so I went digging. We have a fix for these [1]. They were present since 5.18-rc1. >> This seems like a step back when comes to simplifying locking in >> sk_psock_backlog() that was done in 799aa7f98d53. > > Kinda, but it is still true that this sock lock is not for sk_socket > (merely for closing this race condition). I really think the initial idea [2] is much nicer. I can turn it into a patch, if you are short on time. With [1] and [2] applied, the dead lock and memory accounting warnings are gone, when running `test_sockmap`. Thanks, Jakub [1] https://lore.kernel.org/netdev/1667000674-13237-1-git-send-email-wangyufen@huawei.com/ [2] https://lore.kernel.org/netdev/Y0xJUc%2FLRu8K%2FAf8@pop-os.localdomain/
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