ftrace: Fix assuming build time sort works for s390

To speed up the boot process, as mcount_loc needs to be sorted for ftrace
to work properly, sorting it at build time is more efficient than boot up
and can save milliseconds of time. Unfortunately, this change broke s390
as it will modify the mcount_loc location after the sorting takes place
and will put back the unsorted locations. Since the sorting is skipped at
boot up if it is believed that it was sorted at run time, ftrace can crash
as its algorithms are dependent on the list being sorted.

Add a new config BUILDTIME_MCOUNT_SORT that is set when
BUILDTIME_TABLE_SORT but not if S390 is set. Use this config to determine
if sorting should take place at boot up.

Link: https://lore.kernel.org/all/yt9dee51ctfn.fsf@linux.ibm.com/
Fixes: 72b3942a173c ("scripts: ftrace - move the sort-processing in ftrace_init")
Reported-by: Sven Schnelle <svens@linux.ibm.com>
Tested-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index f468767..752ed89 100644 (file)
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -70,6 +70,13 @@ config HAVE_C_RECORDMCOUNT
        help
          C version of recordmcount available?
 
+config BUILDTIME_MCOUNT_SORT
+       bool
+       default y
+       depends on BUILDTIME_TABLE_SORT && !S390
+       help
+         Sort the mcount_loc section at build time.
+
 config TRACER_MAX_TRACE
        bool
 
@@ -918,7 +925,7 @@ config EVENT_TRACE_TEST_SYSCALLS
 config FTRACE_SORT_STARTUP_TEST
        bool "Verify compile time sorting of ftrace functions"
        depends on DYNAMIC_FTRACE
-       depends on BUILDTIME_TABLE_SORT
+       depends on BUILDTIME_MCOUNT_SORT
        help
         Sorting of the mcount_loc sections that is used to find the
         where the ftrace knows where to patch functions for tracing

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 403e485..b01e1fa 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6429,10 +6429,10 @@ static int ftrace_process_locs(struct module *mod,
 
        /*
         * Sorting mcount in vmlinux at build time depend on
-        * CONFIG_BUILDTIME_TABLE_SORT, while mcount loc in
+        * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in
         * modules can not be sorted at build time.
         */
-       if (!IS_ENABLED(CONFIG_BUILDTIME_TABLE_SORT) || mod) {
+       if (!IS_ENABLED(CONFIG_BUILDTIME_MCOUNT_SORT) || mod) {
                sort(start, count, sizeof(*start),
                     ftrace_cmp_ips, NULL);
        } else {