[PATCH for-4.10] pstore: don't OOPS when there are no ftrace zones

From: Brian Norris
Date: Thu Feb 09 2017 - 01:51:15 EST

We'll OOPS in ramoops_get_next_prz() if the platform didn't ask for any
ftrace zones (i.e., cxt->fprzs will be NULL). Let's just skip this
entire FTRACE section if there's no 'fprzs'.

Regression seen on a coreboot/depthcharge-based Chromebook.

Fixes: 2fbea82bbb89 ("pstore: Merge per-CPU ftrace records into one")
Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Brian Norris <briannorris@xxxxxxxxxxxx>
Sorry for the late notice, but I just booted 4.10 on a Chromebook. This also
may not be the "perfect" fix, but it's what I scrounged up in 5 minutes today.

fs/pstore/ram.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 27c059e1760a..1d887efaaf71 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -280,7 +280,7 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
1, id, type, PSTORE_TYPE_PMSG, 0);

/* ftrace is last since it may want to dynamically allocate memory. */
- if (!prz_ok(prz)) {
+ if (!prz_ok(prz) && cxt->fprzs) {
if (!(cxt->flags & RAMOOPS_FLAG_FTRACE_PER_CPU)) {
prz = ramoops_get_next_prz(cxt->fprzs,
&cxt->ftrace_read_cnt, 1, id, type,