linux-kernel - [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

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Date:   Tue, 18 Jun 2019 11:26:28 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Roman Penyaev <rpenyaev@...e.de>,
        Uladzislau Rezki <urezki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Arnd Bergmann <arnd@...db.de>,
        Roman Gushchin <guro@...com>, Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joelaf@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] mm/vmalloc: avoid bogus -Wmaybe-uninitialized warning

gcc gets confused in pcpu_get_vm_areas() because there are too many
branches that affect whether 'lva' was initialized before it gets
used:

mm/vmalloc.c: In function 'pcpu_get_vm_areas':
mm/vmalloc.c:991:4: error: 'lva' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    insert_vmap_area_augment(lva, &va->rb_node,
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     &free_vmap_area_root, &free_vmap_area_list);
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/vmalloc.c:916:20: note: 'lva' was declared here
  struct vmap_area *lva;
                    ^~~

Add an intialization to NULL, and check whether this has changed
before the first use.

Fixes: 68ad4a330433 ("mm/vmalloc.c: keep track of free blocks for vmap allocation")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 mm/vmalloc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a9213fc3802d..42a6f795c3ee 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -913,7 +913,12 @@ adjust_va_to_fit_type(struct vmap_area *va,
 	unsigned long nva_start_addr, unsigned long size,
 	enum fit_type type)
 {
-	struct vmap_area *lva;
+	/*
+	 * GCC cannot always keep track of whether this variable
+	 * was initialized across many branches, therefore set
+	 * it NULL here to avoid a warning.
+	 */
+	struct vmap_area *lva = NULL;
 
 	if (type == FL_FIT_TYPE) {
 		/*
@@ -987,7 +992,7 @@ adjust_va_to_fit_type(struct vmap_area *va,
 	if (type != FL_FIT_TYPE) {
 		augment_tree_propagate_from(va);
 
-		if (type == NE_FIT_TYPE)
+		if (lva)
 			insert_vmap_area_augment(lva, &va->rb_node,
 				&free_vmap_area_root, &free_vmap_area_list);
 	}
-- 
2.20.0