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Wysocki" , Andrew Morton , netdev@vger.kernel.org, "David S . Miller" , Jakub Kicinski , Paolo Abeni , Eric Dumazet , Eric Dumazet We will soon no longer acquire uevent_sock_mutex for most kobject_uevent_net_broadcast() calls, and also while calling uevent_net_broadcast(). Make uevent_seqnum an atomic64_t to get its own protection. This fixes a race while reading /sys/kernel/uevent_seqnum. Signed-off-by: Eric Dumazet Cc: Greg Kroah-Hartman Cc: Christian Brauner Reviewed-by: Christian Brauner --- include/linux/kobject.h | 2 +- kernel/ksysfs.c | 2 +- lib/kobject_uevent.c | 17 +++++++++-------- 3 files changed, 11 insertions(+), 10 deletions(-) diff --git a/include/linux/kobject.h b/include/linux/kobject.h index c30affcc43b444cc17cb894b83b17b52e41f8ebc..c8219505a79f98bc370e52997efc8af51833cfda 100644 --- a/include/linux/kobject.h +++ b/include/linux/kobject.h @@ -38,7 +38,7 @@ extern char uevent_helper[]; #endif /* counter to tag the uevent, read only except for the kobject core */ -extern u64 uevent_seqnum; +extern atomic64_t uevent_seqnum; /* * The actions here must match the index to the string array diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c index 1d4bc493b2f4b2e94133cec75e569bef3f3ead25..32ae7fa74a9c072a44f7280b950b97d25cb07baf 100644 --- a/kernel/ksysfs.c +++ b/kernel/ksysfs.c @@ -39,7 +39,7 @@ static struct kobj_attribute _name##_attr = __ATTR_RW(_name) static ssize_t uevent_seqnum_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { - return sysfs_emit(buf, "%llu\n", (unsigned long long)uevent_seqnum); + return sysfs_emit(buf, "%llu\n", (u64)atomic64_read(&uevent_seqnum)); } KERNEL_ATTR_RO(uevent_seqnum); diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c index fb9a2f06dd1e79db0e5db17362c88152790e2b36..9cb1a7fdaeba4fc5c698fbe84f359fb305345be1 100644 --- a/lib/kobject_uevent.c +++ b/lib/kobject_uevent.c @@ -30,7 +30,7 @@ #include -u64 uevent_seqnum; +atomic64_t uevent_seqnum; #ifdef CONFIG_UEVENT_HELPER char uevent_helper[UEVENT_HELPER_PATH_LEN] = CONFIG_UEVENT_HELPER_PATH; #endif @@ -44,7 +44,7 @@ struct uevent_sock { static LIST_HEAD(uevent_sock_list); #endif -/* This lock protects uevent_seqnum and uevent_sock_list */ +/* This lock protects uevent_sock_list */ static DEFINE_MUTEX(uevent_sock_mutex); /* the strings here must match the enum in include/linux/kobject.h */ @@ -583,13 +583,13 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action, break; } - mutex_lock(&uevent_sock_mutex); /* we will send an event, so request a new sequence number */ - retval = add_uevent_var(env, "SEQNUM=%llu", ++uevent_seqnum); - if (retval) { - mutex_unlock(&uevent_sock_mutex); + retval = add_uevent_var(env, "SEQNUM=%llu", + atomic64_inc_return(&uevent_seqnum)); + if (retval) goto exit; - } + + mutex_lock(&uevent_sock_mutex); retval = kobject_uevent_net_broadcast(kobj, env, action_string, devpath); mutex_unlock(&uevent_sock_mutex); @@ -688,7 +688,8 @@ static int uevent_net_broadcast(struct sock *usk, struct sk_buff *skb, int ret; /* bump and prepare sequence number */ - ret = snprintf(buf, sizeof(buf), "SEQNUM=%llu", ++uevent_seqnum); + ret = snprintf(buf, sizeof(buf), "SEQNUM=%llu", + atomic64_inc_return(&uevent_seqnum)); if (ret < 0 || (size_t)ret >= sizeof(buf)) return -ENOMEM; ret++; From patchwork Wed Feb 14 08:48:29 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric Dumazet X-Patchwork-Id: 13556074 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 32D18B64A for ; 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Wed, 14 Feb 2024 00:48:35 -0800 (PST) Date: Wed, 14 Feb 2024 08:48:29 +0000 In-Reply-To: <20240214084829.684541-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240214084829.684541-1-edumazet@google.com> X-Mailer: git-send-email 2.43.0.687.g38aa6559b0-goog Message-ID: <20240214084829.684541-3-edumazet@google.com> Subject: [PATCH 2/2] kobject: reduce uevent_sock_mutex scope From: Eric Dumazet To: Greg Kroah-Hartman , Christian Brauner Cc: linux-kernel , "Rafael J . Wysocki" , Andrew Morton , netdev@vger.kernel.org, "David S . Miller" , Jakub Kicinski , Paolo Abeni , Eric Dumazet , Eric Dumazet This is a followup of commit a3498436b3a0 ("netns: restrict uevents") - uevent_sock_mutex no longer protects uevent_seqnum thanks to prior patch in the series. - uevent_net_broadcast() can run without holding uevent_sock_mutex. - Instead of grabbing uevent_sock_mutex before calling kobject_uevent_net_broadcast(), we can move the mutex_lock(&uevent_sock_mutex) to the place we iterate over uevent_sock_list : uevent_net_broadcast_untagged(). After this patch, typical netdevice creations and destructions calling uevent_net_broadcast_tagged() no longer need to acquire uevent_sock_mutex. Signed-off-by: Eric Dumazet Cc: Greg Kroah-Hartman Cc: Christian Brauner Reviewed-by: Christian Brauner --- lib/kobject_uevent.c | 9 +++------ 1 file changed, 3 insertions(+), 6 deletions(-) diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c index 9cb1a7fdaeba4fc5c698fbe84f359fb305345be1..03b427e2707e357ab12abeb9da234432c4bc0fb3 100644 --- a/lib/kobject_uevent.c +++ b/lib/kobject_uevent.c @@ -42,10 +42,9 @@ struct uevent_sock { #ifdef CONFIG_NET static LIST_HEAD(uevent_sock_list); -#endif - /* This lock protects uevent_sock_list */ static DEFINE_MUTEX(uevent_sock_mutex); +#endif /* the strings here must match the enum in include/linux/kobject.h */ static const char *kobject_actions[] = { @@ -315,6 +314,7 @@ static int uevent_net_broadcast_untagged(struct kobj_uevent_env *env, int retval = 0; /* send netlink message */ + mutex_lock(&uevent_sock_mutex); list_for_each_entry(ue_sk, &uevent_sock_list, list) { struct sock *uevent_sock = ue_sk->sk; @@ -334,6 +334,7 @@ static int uevent_net_broadcast_untagged(struct kobj_uevent_env *env, if (retval == -ENOBUFS || retval == -ESRCH) retval = 0; } + mutex_unlock(&uevent_sock_mutex); consume_skb(skb); return retval; @@ -589,10 +590,8 @@ int kobject_uevent_env(struct kobject *kobj, enum kobject_action action, if (retval) goto exit; - mutex_lock(&uevent_sock_mutex); retval = kobject_uevent_net_broadcast(kobj, env, action_string, devpath); - mutex_unlock(&uevent_sock_mutex); #ifdef CONFIG_UEVENT_HELPER /* call uevent_helper, usually only enabled during early boot */ @@ -743,9 +742,7 @@ static int uevent_net_rcv_skb(struct sk_buff *skb, struct nlmsghdr *nlh, return -EPERM; } - mutex_lock(&uevent_sock_mutex); ret = uevent_net_broadcast(net->uevent_sock->sk, skb, extack); - mutex_unlock(&uevent_sock_mutex); return ret; }