From: Doug Berger opendmb@gmail.com
[ Upstream commit c51bc12d06b3a5494fbfcbd788a8e307932a06e9 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm/mm/init.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c index a9f6705aea238..731b7e64715b9 100644 --- a/arch/arm/mm/init.c +++ b/arch/arm/mm/init.c @@ -691,7 +691,8 @@ 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); } read_unlock(&tasklist_lock); set_section_perms(perms, n, true, current->active_mm);