ARM: 8874/1: mm: only adjust sections of valid mm structures

A timing hazard exists when an early fork/exec thread begins
exiting and sets its mm pointer to NULL while a separate core
tries to update the section information.

This commit ensures that the mm pointer is not NULL before
setting its section parameters. The arguments provided by
commit 11ce4b33aedc ("ARM: 8672/1: mm: remove tasklist locking
from update_sections_early()") are equally valid for not
requiring grabbing the task_lock around this check.

Fixes: 08925c2f124f ("ARM: 8464/1: Update all mm structures with section adjustments")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Laura Abbott <labbott@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Rob Herring <robh@kernel.org>
Cc: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 16d373d..3a65ded 100644 (file)
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -628,7 +628,8 @@ static void update_sections_early(struct section_perm perms[], int n)
                if (t->flags & PF_KTHREAD)
                        continue;
                for_each_thread(t, s)
-                       set_section_perms(perms, n, true, s->mm);
+                       if (s->mm)
+                               set_section_perms(perms, n, true, s->mm);
        }
        set_section_perms(perms, n, true, current->active_mm);
        set_section_perms(perms, n, true, &init_mm);