This patch implements all logic necessary to match a new trace event that we add against preserved trace events from kho. If we find a match, we give the new trace event the old event's identifier. That way, trace read-outs are able to make sense of buffer contents again because the parsing code for events looks at the same identifiers.
Signed-off-by: Alexander Graf <[email protected]> --- v1 -> v2: - make kho_get_fdt() const - Get events as array from a property, use fingerprint instead of names to identify events - Remove ifdefs --- kernel/trace/trace_output.c | 158 +++++++++++++++++++++++++++++++++++- 1 file changed, 156 insertions(+), 2 deletions(-) diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 7d8815352e20..937002a204e1 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -24,6 +24,8 @@ DECLARE_RWSEM(trace_event_sem); static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly; +static bool trace_is_kho_event(int type); + enum print_line_t trace_print_bputs_msg_only(struct trace_iterator *iter) { struct trace_seq *s = &iter->seq; @@ -784,7 +786,7 @@ static DEFINE_IDA(trace_event_ida); static void free_trace_event_type(int type) { - if (type >= __TRACE_LAST_TYPE) + if (type >= __TRACE_LAST_TYPE && !trace_is_kho_event(type)) ida_free(&trace_event_ida, type); } @@ -810,6 +812,156 @@ void trace_event_read_unlock(void) up_read(&trace_event_sem); } + +/** + * trace_kho_get_map - Return the KHO event map + * @pmap: Pointer to a trace map array. Will be filled on success. + * @plen: Pointer to the length of the map. Will be filled on success. + * @unallocated: True if the event does not have an ID yet + * + * Event types are semi-dynamically generated. To ensure that + * their identifiers match before and after kexec with KHO, + * we store an event map in the KHO DT. Whenever we need the + * map, this function provides it. + * + * The first time we request a map, it also walks through it and + * reserves all identifiers so later event registration has find their + * identifier already reserved. + */ +static int trace_kho_get_map(const struct trace_event_map **pmap, int *plen, + bool unallocated) +{ + static const struct trace_event_map *event_map; + static int event_map_len; + static bool event_map_reserved; + const struct trace_event_map *map = NULL; + const void *fdt = kho_get_fdt(); + const char *path = "/ftrace"; + int off, err, len = 0; + int i; + + if (!IS_ENABLED(CONFIG_FTRACE_KHO) || !fdt) + return -EINVAL; + + if (event_map) { + map = event_map; + len = event_map_len; + } + + if (!map) { + off = fdt_path_offset(fdt, path); + + if (off < 0) { + pr_debug("Could not find '%s' in DT", path); + return -EINVAL; + } + + err = fdt_node_check_compatible(fdt, off, "ftrace-v1"); + if (err) { + pr_warn("Node '%s' has invalid compatible", path); + return -EINVAL; + } + + map = fdt_getprop(fdt, off, "events", &len); + if (!map) + return -EINVAL; + + event_map = map; + event_map_len = len; + } + + if (unallocated && !event_map_reserved) { + /* + * Reserve all IDs in our IDA. We only have a working IDA later + * in boot, so restrict it to when we allocate a dynamic type id + * for an event. + */ + for (i = 0; i < len; i += sizeof(*map)) { + const struct trace_event_map *imap = (void *)map + i; + + if (imap->type < __TRACE_LAST_TYPE) + continue; + if (ida_alloc_range(&trace_event_ida, imap->type, imap->type, + GFP_KERNEL) != imap->type) { + pr_warn("Unable to reserve id %d", imap->type); + return -EINVAL; + } + } + + event_map_reserved = true; + } + + *pmap = map; + *plen = len; + + return 0; +} + +/** + * trace_is_kho_event - returns true if the event type is KHO reserved + * @event: the event type to enumerate + * + * With KHO, we reserve all previous kernel's trace event types in the + * KHO DT. Then, when we allocate a type, we just reuse the previous + * kernel's value. However, that means we have to keep these type identifiers + * reserved across the lifetime of the system, because we may get a new event + * that matches the old kernel's event fingerprint. This function is a small + * helper that allows us to check whether a type ID is in use by KHO. + */ +static bool trace_is_kho_event(int type) +{ + const struct trace_event_map *map = NULL; + int len, i; + + if (trace_kho_get_map(&map, &len, false)) + return false; + + if (!map) + return false; + + for (i = 0; i < len; i += sizeof(*map), map++) + if (map->type == type) + return true; + + return false; +} + +/** + * trace_kho_fill_event_type - restore event type info from KHO + * @event: the event to enumerate + * + * Event types are semi-dynamically generated. To ensure that + * their identifiers match before and after kexec with KHO, + * let's match up unique fingerprint - either their predetermined + * type or their crc32 value - and fill in the respective type + * information if we booted with KHO. + */ +static bool trace_kho_fill_event_type(struct trace_event *event) +{ + const struct trace_event_map *map = NULL; + int len = 0, i; + u32 crc32; + + if (trace_kho_get_map(&map, &len, !event->type)) + return false; + + crc32 = event2fp(event); + + for (i = 0; i < len; i += sizeof(*map), map++) { + if (map->crc32 == crc32) { + if (!map->type) + return false; + + event->type = map->type; + return true; + } + } + + pr_debug("Could not find event"); + + return false; +} + /** * register_trace_event - register output for an event type * @event: the event type to register @@ -838,7 +990,9 @@ int register_trace_event(struct trace_event *event) if (WARN_ON(!event->funcs)) goto out; - if (!event->type) { + if (trace_kho_fill_event_type(event)) { + pr_debug("Recovered id=%d", event->type); + } else if (!event->type) { event->type = alloc_trace_event_type(); if (!event->type) goto out; -- 2.40.1 Amazon Development Center Germany GmbH Krausenstr. 38 10117 Berlin Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B Sitz: Berlin Ust-ID: DE 289 237 879
