From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from stravinsky.debian.org (stravinsky.debian.org [82.195.75.108]) (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 015003D9545; Wed, 5 Aug 2026 10:59:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=82.195.75.108 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785927557; cv=none; b=F/D5gvhL1pEj4R4cwU8FrMd9n8DsR/lr5re7Vx2Rg+XTNjyARfm5mwA3vxzYQWnSTsCCgCqtrEtvN0OyCTMVtnv9Um/KbY4GEjTnt5rJWZV5XPD3KPJJh5cdxmT7FX7d9gcbq9Sn3jONU5wWZTjSssREoTMR0Pq7m+sMtJ2pehw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785927557; c=relaxed/simple; bh=wLGKCNog8+m8abD/kjwLtMo1+vBYXg7HqfBu+BVQlhY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References: In-Reply-To:To:Cc; b=iVyNEXhlty/wvmoQffhKvM0Qg6RByhSsqKvGKwYPsU71diiEMVPCRUMEL0X2uBF7i2bZ3W8NvB0rzwkq+N2hVfYeKTnd+uq9P4CLM/Tw1p54ed6UdmdzXuK+PzypaDhgs7IOVw2RbqaZ5wDQqllX5NcdSRYMLxevdFL0wy7pXJ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org; spf=pass smtp.mailfrom=debian.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b=rLrqYqYw; arc=none smtp.client-ip=82.195.75.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=debian.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=debian.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=debian.org header.i=@debian.org header.b="rLrqYqYw" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=debian.org; s=smtpauto.stravinsky; h=X-Debian-User:Cc:To:In-Reply-To:References: Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Reply-To:Content-ID:Content-Description; bh=gNVUO/AfyFVjoPlB6G7IBcBKUi8NdH5E7PNb7ECR5qs=; b=rLrqYqYwSUtb+OKaJ2lk4xPDRL ZD6YRWPZtnZbUywf0P2BKFniIajBpl4U7y/rEI9YZvH360UO1lgFU6cUrG/RWI04Fh5BNwfZk+TpO CrsxZeY7EEju4QVFb56wciH1u6JR59jElrEsxLKu73yj50GgTBcGiJEtim/R4szLc2ErAjm/g95dm spqCnrVJnXiqzQ2vTqR9BQFBwMHbr65aFi8hn8r93nAEyxgUwwrmmDCXDFLQk+qh+wLYz/16yi6ky gy168fEoE0aAr2IR0ofDnmtW8cCmgsSIFPMLGIT5M96L7s5+IFvopmMxnks0gM2C2dICjUW5mzzom Ui0hb4Iw==; Received: from authenticated-user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1wrZL2-00Drzs-1V; Wed, 05 Aug 2026 10:59:08 +0000 From: Breno Leitao Date: Wed, 05 Aug 2026 03:58:19 -0700 Subject: [PATCH net-next v2 1/2] netconsole: publish the userdata payload with RCU Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260805-netcons-userdata-rcu-v2-1-c5e80f6a7a46@debian.org> References: <20260805-netcons-userdata-rcu-v2-0-c5e80f6a7a46@debian.org> In-Reply-To: <20260805-netcons-userdata-rcu-v2-0-c5e80f6a7a46@debian.org> To: Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Shuah Khan Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, gustavold@gmail.com, asantostc@gmail.com, Breno Leitao , kernel-team@meta.com X-Mailer: b4 0.16-dev-f8e9d X-Developer-Signature: v=1; a=openpgp-sha256; l=8446; i=leitao@debian.org; h=from:subject:message-id; bh=wLGKCNog8+m8abD/kjwLtMo1+vBYXg7HqfBu+BVQlhY=; b=owEBbAKT/ZANAwAIATWjk5/8eHdtAcsmYgBqcxdyf54+EOKh3YdxSFJ0vrx0oHlHf7q+3Gg3+ KN8qV4Rg82JAjIEAAEIAB0WIQSshTmm6PRnAspKQ5s1o5Of/Hh3bQUCanMXcgAKCRA1o5Of/Hh3 bdV6D/id2gANdUoavcPxE9kS6WOZcoSOm7zajfEMnR9v0pQf35Bh1iK793km+6zlWc1A82ujYu7 dQVp5WWN7UVXbY9l5DTBdPnELYHOQevecuMPMSTb9tIGJkj/OKmMUDAouoTuGuFi/L/MmlURYIP hAejKK71WXkQWxoEIsm99WMr8bi8hHCHuwONIn04v/JfELfNmpStNzbjwiIK9v9MpIZEsD9BtlQ Er2ifw4CgOvZd+H744+fzKc1WRE14PSIhXNZUvc0F0zoc8t8z/HpVFW9Yhg/hWFGOrofhacFLoh 6BT/6gwwiawWQeV0Us4KxjlwzRoxTzAnjQr/Feu0ouUa4fCTawZabC+D3zReBJWUGIx+WTMOnqB vgRSY3FeCFPqvP/Dp+gwzP+mOfP2Q98ni77qM/LBJUdKHWnHAXNFUvpKPW77deswaHuUcUI2XAH 4KhQZDlOK6Takpxrktqx04dGxb3rsxvK8EZribXB3oDN2YQaIhGdvHrE+N5eZhuLpDQlfRcr/f8 +FLbtVdnsoWHux/0ufpZBLupbt9nzKeZk3bVZ+/TM09p+x3XcxUP7aIAdjmqR0LKx5xr48mqAFL 4B9PndI47FVixLSJ0ruWRBUXznXpi9I2JAMdAagUIimeeiYp91aIdR0rUDTTEr919Vad6PYPlZK ZnRaFrbhK0RNv X-Developer-Key: i=leitao@debian.org; a=openpgp; fpr=AC8539A6E8F46702CA4A439B35A3939FFC78776D X-Debian-User: leitao update_userdata() takes target_list_lock to swap nt->userdata and nt->userdata_length, then frees the old buffer. Since commit 7eab73b18630 ("netconsole: convert to NBCON console infrastructure") that lock is also the console's device_lock, so writing a userdata value from configfs serialises against the printk core emitting messages. The buffer is immutable once published, which is what RCU is for. Move the string and its length into a single netcons_userdata object and publish it with rcu_replace_pointer(), freeing the old one with kfree_rcu(). New userdata design: 0) Unify the userdata fields into a struct netcons_userdata 1) update_userdata() no longer needs target_list_lock. 2) writers stay serialised by dynamic_netconsole_mutex. 3) reading userdata needs an RCU read lock. No functional change intended. Signed-off-by: Breno Leitao --- drivers/net/netconsole.c | 92 +++++++++++++++++++++++++++++------------------- 1 file changed, 56 insertions(+), 36 deletions(-) diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c index 862001d09aa84..14092fb15f6d0 100644 --- a/drivers/net/netconsole.c +++ b/drivers/net/netconsole.c @@ -135,13 +135,27 @@ enum target_state { STATE_DEACTIVATED, }; +/** + * struct netcons_userdata - Formatted userdata payload of a target. + * @rcu: Used to free the payload after a grace period. + * @length: Length of @data, excluding the NUL terminator. + * @data: Formatted " key=value\n" entries, NUL terminated. + * + * Immutable once published, so the transmit path never observes @data and + * @length disagreeing. + */ +struct netcons_userdata { + struct rcu_head rcu; + size_t length; + char data[]; +}; + /** * struct netconsole_target - Represents a configured netconsole target. * @list: Links this target into the target_list. * @group: Links us into the configfs subsystem hierarchy. * @userdata_group: Links to the userdata configfs hierarchy - * @userdata: Cached, formatted string of append - * @userdata_length: String length of userdata. + * @userdata: Cached, formatted userdata payload. RCU protected. * @sysdata: Cached, formatted string of append * @sysdata_fields: Sysdata features enabled. * @msgcounter: Message sent counter. @@ -176,8 +190,7 @@ struct netconsole_target { #ifdef CONFIG_NETCONSOLE_DYNAMIC struct config_group group; struct config_group userdata_group; - char *userdata; - size_t userdata_length; + struct netcons_userdata __rcu *userdata; char sysdata[MAX_EXTRADATA_ENTRY_LEN * MAX_SYSDATA_ITEMS]; /* bit-wise with sysdata_feature bits */ @@ -1059,12 +1072,11 @@ static int calc_userdata_len(struct netconsole_target *nt) static int update_userdata(struct netconsole_target *nt) { + struct netcons_userdata *new = NULL; + struct netcons_userdata *old; struct userdatum *udm_item; struct config_item *item; struct list_head *entry; - char *old_buf = NULL; - char *new_buf = NULL; - unsigned long flags; int offset = 0; int len; @@ -1076,8 +1088,8 @@ static int update_userdata(struct netconsole_target *nt) /* Allocate new buffer */ if (len) { - new_buf = kmalloc(len + 1, GFP_KERNEL); - if (!new_buf) + new = kmalloc_flex(*new, data, len + 1); + if (!new) return -ENOMEM; } @@ -1087,22 +1099,21 @@ static int update_userdata(struct netconsole_target *nt) udm_item = to_userdatum(item); /* Skip userdata with no value set */ if (udm_item->value[0]) { - offset += scnprintf(&new_buf[offset], len + 1 - offset, + offset += scnprintf(&new->data[offset], + len + 1 - offset, " %s=%s\n", item->ci_name, udm_item->value); } } WARN_ON_ONCE(offset != len); + if (new) + new->length = offset; - /* Switch to new buffer and free old buffer */ - spin_lock_irqsave(&target_list_lock, flags); - old_buf = nt->userdata; - nt->userdata = new_buf; - nt->userdata_length = offset; - spin_unlock_irqrestore(&target_list_lock, flags); - - kfree(old_buf); + /* Writers are serialized by dynamic_netconsole_mutex. */ + old = rcu_replace_pointer(nt->userdata, new, + lockdep_is_held(&dynamic_netconsole_mutex)); + kfree_rcu(old, rcu); return 0; } @@ -1392,7 +1403,7 @@ static void netconsole_target_release(struct config_item *item) { struct netconsole_target *nt = to_target(item); - kfree(nt->userdata); + kfree(rcu_access_pointer(nt->userdata)); kfree(nt); } @@ -1926,14 +1937,13 @@ static void send_udp(struct netconsole_target *nt, const char *msg, int len) static void send_msg_no_fragmentation(struct netconsole_target *nt, const char *msg, int msg_len, - int release_len) + int release_len, + const struct netcons_userdata *userdata) { - const char *userdata = NULL; const char *sysdata = NULL; const char *release; #ifdef CONFIG_NETCONSOLE_DYNAMIC - userdata = nt->userdata; sysdata = nt->sysdata; #endif @@ -1950,7 +1960,7 @@ static void send_msg_no_fragmentation(struct netconsole_target *nt, if (userdata) msg_len += scnprintf(&nt->buf[msg_len], sizeof(nt->buf) - msg_len, "%s", - userdata); + userdata->data); if (sysdata) msg_len += scnprintf(&nt->buf[msg_len], @@ -1970,7 +1980,8 @@ static void append_release(char *buf) static void send_fragmented_body(struct netconsole_target *nt, const char *msgbody_ptr, int header_len, - int msgbody_len, int sysdata_len) + int msgbody_len, int sysdata_len, + const struct netcons_userdata *userdata) { const char *userdata_ptr = NULL; const char *sysdata_ptr = NULL; @@ -1981,12 +1992,12 @@ static void send_fragmented_body(struct netconsole_target *nt, int userdata_len = 0; #ifdef CONFIG_NETCONSOLE_DYNAMIC - userdata_ptr = nt->userdata; sysdata_ptr = nt->sysdata; - userdata_len = nt->userdata_length; #endif - if (WARN_ON_ONCE(!userdata_ptr && userdata_len != 0)) - return; + if (userdata) { + userdata_ptr = userdata->data; + userdata_len = userdata->length; + } if (WARN_ON_ONCE(!sysdata_ptr && sysdata_len != 0)) return; @@ -2063,7 +2074,8 @@ static void send_msg_fragmented(struct netconsole_target *nt, const char *msg, int msg_len, int release_len, - int sysdata_len) + int sysdata_len, + const struct netcons_userdata *userdata) { int header_len, msgbody_len; const char *msgbody; @@ -2092,7 +2104,7 @@ static void send_msg_fragmented(struct netconsole_target *nt, * will be replaced */ send_fragmented_body(nt, msgbody, header_len, msgbody_len, - sysdata_len); + sysdata_len, userdata); } /** @@ -2107,25 +2119,33 @@ static void send_msg_fragmented(struct netconsole_target *nt, static void send_ext_msg_udp(struct netconsole_target *nt, struct nbcon_write_context *wctxt) { + const struct netcons_userdata *userdata = NULL; int userdata_len = 0; int release_len = 0; int sysdata_len = 0; int len; + /* Keeps the payload picked below alive until the last send_udp(). */ + rcu_read_lock(); + #ifdef CONFIG_NETCONSOLE_DYNAMIC sysdata_len = prepare_sysdata(nt, wctxt); - userdata_len = nt->userdata_length; + userdata = rcu_dereference(nt->userdata); + if (userdata) + userdata_len = userdata->length; #endif if (nt->release) release_len = strlen(init_utsname()->release) + 1; len = wctxt->len + release_len + sysdata_len + userdata_len; if (len <= MAX_PRINT_CHUNK) - return send_msg_no_fragmentation(nt, wctxt->outbuf, - wctxt->len, release_len); + send_msg_no_fragmentation(nt, wctxt->outbuf, wctxt->len, + release_len, userdata); + else + send_msg_fragmented(nt, wctxt->outbuf, wctxt->len, release_len, + sysdata_len, userdata); - return send_msg_fragmented(nt, wctxt->outbuf, wctxt->len, release_len, - sysdata_len); + rcu_read_unlock(); } static void send_msg_udp(struct netconsole_target *nt, const char *msg, @@ -2357,7 +2377,7 @@ static void free_param_target(struct netconsole_target *nt) cancel_work_sync(&nt->resume_wq); netpoll_cleanup(&nt->np); #ifdef CONFIG_NETCONSOLE_DYNAMIC - kfree(nt->userdata); + kfree(rcu_access_pointer(nt->userdata)); #endif kfree(nt); } -- 2.53.0-Meta