From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id ED08A1FF61E; Wed, 21 May 2025 14:52:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747839135; cv=none; b=MlufZkWp7O5TzOfyXAvXjH58NyPh/OJlapj9KUlskiXft4cSxZMyMaykBKGWh0Rn/Dz7GZq8P5tD9u9cOiqoC0PE64cctvnvY5Ao2BoLJA4IJT2cWIeTkBZYri1ADuqTO9mJHFZjADtSH37l0A0k7tqcMnh03f5rGdfI/h/9izM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747839135; c=relaxed/simple; bh=Cj77OU4/P+Re9+XycqfKs1pRkE+Tyv4YPPPvDrFfbYM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=fjKke2FFkmZqqjQ0v3huoEEFj5JklYl0zoF0XJbjzYYOgzWFpYGL6L9JgHCmzLt1hwSHxQVHRK8UfU/O+0jUOqusUuZKfH79/Q0XqrDrivtX4mrkduV4CBEhFUEPpJRcnxSlzO++YW1jz2ruVDTWubIgYK67YVyNx2X/pcVZ+PE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jT33xGSt; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="jT33xGSt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2A21C4CEE4; Wed, 21 May 2025 14:52:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747839134; bh=Cj77OU4/P+Re9+XycqfKs1pRkE+Tyv4YPPPvDrFfbYM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jT33xGSt2sT+jMeCZx+oiEjeZfdxTxD2wPqJLvLdPIff5VHMH9U22T+WnkR6qcdkF LoZvWgLnvT6BfuXzA2zhaAOwJITrVUi7h6OtTY/3TcuAWPpYNrm/logPJwyAsRVdyp LddDyrtLP3vyFuPszeoduKNNZsUTvvTuSb6I1CrpJdPNB1UtakACEkc12OIyamUvl9 CiadC2BNC1+cGM+nvowsWWqIQOKMR36fkeiPfqNXLiPOAvjxKjQ7eq09KbO/PF8RTX zgzcl4qsUuuDoyIWzuICMxOvUiiA5SSHjox6gZ0fU8cbRSyFtmOBjdsnR/ouUwCe0w /TZvxDRCF13kw== From: Lee Jones To: lee@kernel.org, "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Kuniyuki Iwashima , Jens Axboe , Sasha Levin , Michal Luczaj , Rao Shoaib , Pavel Begunkov , linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: stable@vger.kernel.org, kernel test robot Subject: [PATCH v6.6 22/26] af_unix: Try not to hold unix_gc_lock during accept(). Date: Wed, 21 May 2025 14:45:30 +0000 Message-ID: <20250521144803.2050504-23-lee@kernel.org> X-Mailer: git-send-email 2.49.0.1112.g889b7c5bd8-goog In-Reply-To: <20250521144803.2050504-1-lee@kernel.org> References: <20250521144803.2050504-1-lee@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kuniyuki Iwashima [ Upstream commit fd86344823b521149bb31d91eba900ba3525efa6 ] Commit dcf70df2048d ("af_unix: Fix up unix_edge.successor for embryo socket.") added spin_lock(&unix_gc_lock) in accept() path, and it caused regression in a stress test as reported by kernel test robot. If the embryo socket is not part of the inflight graph, we need not hold the lock. To decide that in O(1) time and avoid the regression in the normal use case, 1. add a new stat unix_sk(sk)->scm_stat.nr_unix_fds 2. count the number of inflight AF_UNIX sockets in the receive queue under unix_state_lock() 3. move unix_update_edges() call under unix_state_lock() 4. avoid locking if nr_unix_fds is 0 in unix_update_edges() Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202404101427.92a08551-oliver.sang@intel.com Signed-off-by: Kuniyuki Iwashima Link: https://lore.kernel.org/r/20240413021928.20946-1-kuniyu@amazon.com Signed-off-by: Paolo Abeni (cherry picked from commit fd86344823b521149bb31d91eba900ba3525efa6) Signed-off-by: Lee Jones --- include/net/af_unix.h | 1 + net/unix/af_unix.c | 2 +- net/unix/garbage.c | 20 ++++++++++++++++---- 3 files changed, 18 insertions(+), 5 deletions(-) diff --git a/include/net/af_unix.h b/include/net/af_unix.h index 47042de4a2a9c..b6eedf7650da5 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -67,6 +67,7 @@ struct unix_skb_parms { struct scm_stat { atomic_t nr_fds; + unsigned long nr_unix_fds; }; #define UNIXCB(skb) (*(struct unix_skb_parms *)&((skb)->cb)) diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c index df70d8a7ee837..236a2cd2bc93d 100644 --- a/net/unix/af_unix.c +++ b/net/unix/af_unix.c @@ -1703,12 +1703,12 @@ static int unix_accept(struct socket *sock, struct socket *newsock, int flags, } tsk = skb->sk; - unix_update_edges(unix_sk(tsk)); skb_free_datagram(sk, skb); wake_up_interruptible(&unix_sk(sk)->peer_wait); /* attach accepted sock to socket */ unix_state_lock(tsk); + unix_update_edges(unix_sk(tsk)); newsock->state = SS_CONNECTED; unix_sock_inherit_flags(sock, newsock); sock_graft(tsk, newsock); diff --git a/net/unix/garbage.c b/net/unix/garbage.c index 12a4ec27e0d4d..95240a59808f2 100644 --- a/net/unix/garbage.c +++ b/net/unix/garbage.c @@ -209,6 +209,7 @@ void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver) unix_add_edge(fpl, edge); } while (i < fpl->count_unix); + receiver->scm_stat.nr_unix_fds += fpl->count_unix; WRITE_ONCE(unix_tot_inflight, unix_tot_inflight + fpl->count_unix); out: WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight + fpl->count); @@ -222,6 +223,7 @@ void unix_add_edges(struct scm_fp_list *fpl, struct unix_sock *receiver) void unix_del_edges(struct scm_fp_list *fpl) { + struct unix_sock *receiver; int i = 0; spin_lock(&unix_gc_lock); @@ -235,6 +237,8 @@ void unix_del_edges(struct scm_fp_list *fpl) unix_del_edge(fpl, edge); } while (i < fpl->count_unix); + receiver = fpl->edges[0].successor; + receiver->scm_stat.nr_unix_fds -= fpl->count_unix; WRITE_ONCE(unix_tot_inflight, unix_tot_inflight - fpl->count_unix); out: WRITE_ONCE(fpl->user->unix_inflight, fpl->user->unix_inflight - fpl->count); @@ -246,10 +250,18 @@ void unix_del_edges(struct scm_fp_list *fpl) void unix_update_edges(struct unix_sock *receiver) { - spin_lock(&unix_gc_lock); - unix_update_graph(unix_sk(receiver->listener)->vertex); - receiver->listener = NULL; - spin_unlock(&unix_gc_lock); + /* nr_unix_fds is only updated under unix_state_lock(). + * If it's 0 here, the embryo socket is not part of the + * inflight graph, and GC will not see it, so no lock needed. + */ + if (!receiver->scm_stat.nr_unix_fds) { + receiver->listener = NULL; + } else { + spin_lock(&unix_gc_lock); + unix_update_graph(unix_sk(receiver->listener)->vertex); + receiver->listener = NULL; + spin_unlock(&unix_gc_lock); + } } int unix_prepare_fpl(struct scm_fp_list *fpl) -- 2.49.0.1112.g889b7c5bd8-goog