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ARM: 8672/1: mm: remove tasklist locking from update_sections_early()

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The below backtrace can be observed on -rt kernel with
CONFIG_DEBUG_MODULE_RONX (4.9 kernel CONFIG_DEBUG_RODATA) option enabled:

 BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:993
 in_atomic(): 1, irqs_disabled(): 128, pid: 14, name: migration/0
 1 lock held by migration/0/14:
  #0:  (tasklist_lock){+.+...}, at: [<c01183e8>] update_sections_early+0x24/0xdc
 irq event stamp: 38
 hardirqs last  enabled at (37): [<c08f6f7c>] _raw_spin_unlock_irq+0x24/0x68
 hardirqs last disabled at (38): [<c01fdfe8>] multi_cpu_stop+0xd8/0x138
 softirqs last  enabled at (0): [<c01303ec>] copy_process.part.5+0x238/0x1b64
 softirqs last disabled at (0): [<  (null)>]   (null)
 Preemption disabled at: [<c01fe244>] cpu_stopper_thread+0x80/0x10c
 CPU: 0 PID: 14 Comm: migration/0 Not tainted 4.9.21-rt16-02220-g49e319c #15
 Hardware name: Generic DRA74X (Flattened Device Tree)
 [<c0112014>] (unwind_backtrace) from [<c010d370>] (show_stack+0x10/0x14)
 [<c010d370>] (show_stack) from [<c049beb8>] (dump_stack+0xa8/0xd4)
 [<c049beb8>] (dump_stack) from [<c01631a0>] (___might_sleep+0x1bc/0x2ac)
 [<c01631a0>] (___might_sleep) from [<c08f7244>] (__rt_spin_lock+0x1c/0x30)
 [<c08f7244>] (__rt_spin_lock) from [<c08f77a4>] (rt_read_lock+0x54/0x68)
 [<c08f77a4>] (rt_read_lock) from [<c01183e8>] (update_sections_early+0x24/0xdc)
 [<c01183e8>] (update_sections_early) from [<c01184b0>] (__fix_kernmem_perms+0x10/0x1c)
 [<c01184b0>] (__fix_kernmem_perms) from [<c01fe010>] (multi_cpu_stop+0x100/0x138)
 [<c01fe010>] (multi_cpu_stop) from [<c01fe24c>] (cpu_stopper_thread+0x88/0x10c)
 [<c01fe24c>] (cpu_stopper_thread) from [<c015edc4>] (smpboot_thread_fn+0x174/0x31c)
 [<c015edc4>] (smpboot_thread_fn) from [<c015a988>] (kthread+0xf0/0x108)
 [<c015a988>] (kthread) from [<c0108818>] (ret_from_fork+0x14/0x3c)
 Freeing unused kernel memory: 1024K (c0d00000 - c0e00000)

The stop_machine() is called with cpus = NULL from fix_kernmem_perms() and
mark_rodata_ro() which means only one CPU will execute
update_sections_early() while all other CPUs will spin and wait. Hence,
it's safe to remove tasklist locking from update_sections_early(). As part
of this change also mark functions which are local to this module as
static.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Laura Abbott <labbott@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
This commit is contained in:
Grygorii Strashko 2017-04-25 21:20:52 +01:00 committed by Russell King
parent b70cd406d7
commit 11ce4b33ae
1 changed files with 8 additions and 5 deletions
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13
arch/arm/mm/init.c
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@ -709,34 +709,37 @@ void set_section_perms(struct section_perm *perms, int n, bool set,
} }
/**
* update_sections_early intended to be called only through stop_machine
* framework and executed by only one CPU while all other CPUs will spin and
* wait, so no locking is required in this function.
*/
static void update_sections_early(struct section_perm perms[], int n) static void update_sections_early(struct section_perm perms[], int n)
{ {
struct task_struct *t, *s; struct task_struct *t, *s;
read_lock(&tasklist_lock);
for_each_process(t) { for_each_process(t) {
if (t->flags & PF_KTHREAD) if (t->flags & PF_KTHREAD)
continue; continue;
for_each_thread(t, s) for_each_thread(t, s)
set_section_perms(perms, n, true, s->mm); set_section_perms(perms, n, true, s->mm);
} }
read_unlock(&tasklist_lock);
set_section_perms(perms, n, true, current->active_mm); set_section_perms(perms, n, true, current->active_mm);
set_section_perms(perms, n, true, &init_mm); set_section_perms(perms, n, true, &init_mm);
} }
int __fix_kernmem_perms(void *unused) static int __fix_kernmem_perms(void *unused)
{ {
update_sections_early(nx_perms, ARRAY_SIZE(nx_perms)); update_sections_early(nx_perms, ARRAY_SIZE(nx_perms));
return 0; return 0;
} }
void fix_kernmem_perms(void) static void fix_kernmem_perms(void)
{ {
stop_machine(__fix_kernmem_perms, NULL, NULL); stop_machine(__fix_kernmem_perms, NULL, NULL);
} }
int __mark_rodata_ro(void *unused) static int __mark_rodata_ro(void *unused)
{ {
update_sections_early(ro_perms, ARRAY_SIZE(ro_perms)); update_sections_early(ro_perms, ARRAY_SIZE(ro_perms));
return 0; return 0;