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 netconsole_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 <[email protected]> --- drivers/net/netconsole.c | 88 +++++++++++++++++++++++++++++------------------- 1 file changed, 54 insertions(+), 34 deletions(-) diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c index 862001d09aa84..c88c82f2136cb 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; } @@ -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, -- 2.53.0-Meta
