linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early()
@ 2017-04-18 20:48 Grygorii Strashko
  2017-04-19  0:15 ` Kees Cook
  0 siblings, 1 reply; 4+ messages in thread
From: Grygorii Strashko @ 2017-04-18 20:48 UTC (permalink / raw)
  To: Russell King, Sebastian Andrzej Siewior, linux-rt-users
  Cc: linux-arm-kernel, linux-kernel, Grygorii Strashko, Kees Cook,
	Laura Abbott

The below backtrace can be observed on -rt kernel with 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
to simplify code analize in the future.

Cc: Kees Cook <keescook@chromium.org>
Cc: Laura Abbott <labbott@redhat.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
---
 arch/arm/mm/init.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index 370581a..a77953a 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -693,30 +693,28 @@ static void update_sections_early(struct section_perm perms[], int n)
 {
 	struct task_struct *t, *s;
 
-	read_lock(&tasklist_lock);
 	for_each_process(t) {
 		if (t->flags & PF_KTHREAD)
 			continue;
 		for_each_thread(t, s)
 			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, &init_mm);
 }
 
-int __fix_kernmem_perms(void *unused)
+static int __fix_kernmem_perms(void *unused)
 {
 	update_sections_early(nx_perms, ARRAY_SIZE(nx_perms));
 	return 0;
 }
 
-void fix_kernmem_perms(void)
+static void fix_kernmem_perms(void)
 {
 	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));
 	return 0;
-- 
2.10.1

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early()
  2017-04-18 20:48 [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early() Grygorii Strashko
@ 2017-04-19  0:15 ` Kees Cook
  2017-04-19 19:58   ` Grygorii Strashko
  0 siblings, 1 reply; 4+ messages in thread
From: Kees Cook @ 2017-04-19  0:15 UTC (permalink / raw)
  To: Grygorii Strashko
  Cc: Russell King, Sebastian Andrzej Siewior, linux-rt-users,
	linux-arm-kernel, LKML, Laura Abbott

On Tue, Apr 18, 2017 at 1:48 PM, Grygorii Strashko
<grygorii.strashko@ti.com> wrote:
> The below backtrace can be observed on -rt kernel with 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
> to simplify code analize in the future.

Hm, yes, good point. It's only every called while other CPUs are stopped.

>
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Laura Abbott <labbott@redhat.com>
> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
> ---
>  arch/arm/mm/init.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> index 370581a..a77953a 100644
> --- a/arch/arm/mm/init.c
> +++ b/arch/arm/mm/init.c
> @@ -693,30 +693,28 @@ static void update_sections_early(struct section_perm perms[], int n)

Maybe this should be renamed update_sections_stopped()? Or at least
comments added to help see why it's safe.

>  {
>         struct task_struct *t, *s;
>
> -       read_lock(&tasklist_lock);
>         for_each_process(t) {
>                 if (t->flags & PF_KTHREAD)
>                         continue;
>                 for_each_thread(t, s)
>                         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, &init_mm);
>  }
>
> -int __fix_kernmem_perms(void *unused)
> +static int __fix_kernmem_perms(void *unused)
>  {
>         update_sections_early(nx_perms, ARRAY_SIZE(nx_perms));
>         return 0;
>  }
>
> -void fix_kernmem_perms(void)
> +static void fix_kernmem_perms(void)
>  {
>         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));
>         return 0;

Yeah, the static marks are all correct, thanks for fixing these!

-Kees

-- 
Kees Cook
Pixel Security

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early()
  2017-04-19  0:15 ` Kees Cook
@ 2017-04-19 19:58   ` Grygorii Strashko
  2017-04-19 20:01     ` Kees Cook
  0 siblings, 1 reply; 4+ messages in thread
From: Grygorii Strashko @ 2017-04-19 19:58 UTC (permalink / raw)
  To: Kees Cook
  Cc: Russell King, Sebastian Andrzej Siewior, linux-rt-users,
	linux-arm-kernel, LKML, Laura Abbott



On 04/18/2017 07:15 PM, Kees Cook wrote:
> On Tue, Apr 18, 2017 at 1:48 PM, Grygorii Strashko
> <grygorii.strashko@ti.com> wrote:
>> The below backtrace can be observed on -rt kernel with 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
>> to simplify code analize in the future.
> 
> Hm, yes, good point. It's only every called while other CPUs are stopped.
> 
>>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Laura Abbott <labbott@redhat.com>
>> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
>> ---
>>  arch/arm/mm/init.c | 8 +++-----
>>  1 file changed, 3 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>> index 370581a..a77953a 100644
>> --- a/arch/arm/mm/init.c
>> +++ b/arch/arm/mm/init.c

/**
 * update_sections_early intended to be called only through stop_machine 
 * framework and be executed by only one CPU while all other CPUs will spin and
 * wait, so no locking is required in this function.
 */
>> @@ -693,30 +693,28 @@ static void update_sections_early(struct section_perm perms[], int n)
> 
> Maybe this should be renamed update_sections_stopped()? Or at least
> comments added to help see why it's safe.

would it be ok if I add above comment before update_sections_early?
Also I can rename it to update_sections_stopped() if you want - not sure about the name.


> 
>>  {
>>         struct task_struct *t, *s;
>>
>> -       read_lock(&tasklist_lock);
>>         for_each_process(t) {
>>                 if (t->flags & PF_KTHREAD)
>>                         continue;
>>                 for_each_thread(t, s)
>>                         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, &init_mm);
>>  }
>>
>> -int __fix_kernmem_perms(void *unused)
>> +static int __fix_kernmem_perms(void *unused)
>>  {
>>         update_sections_early(nx_perms, ARRAY_SIZE(nx_perms));
>>         return 0;
>>  }
>>
>> -void fix_kernmem_perms(void)
>> +static void fix_kernmem_perms(void)
>>  {
>>         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));
>>         return 0;
> 
> Yeah, the static marks are all correct, thanks for fixing these!
> 
> -Kees
> 

-- 
regards,
-grygorii

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early()
  2017-04-19 19:58   ` Grygorii Strashko
@ 2017-04-19 20:01     ` Kees Cook
  0 siblings, 0 replies; 4+ messages in thread
From: Kees Cook @ 2017-04-19 20:01 UTC (permalink / raw)
  To: Grygorii Strashko
  Cc: Russell King, Sebastian Andrzej Siewior, linux-rt-users,
	linux-arm-kernel, LKML, Laura Abbott

On Wed, Apr 19, 2017 at 12:58 PM, Grygorii Strashko
<grygorii.strashko@ti.com> wrote:
>
>
> On 04/18/2017 07:15 PM, Kees Cook wrote:
>> On Tue, Apr 18, 2017 at 1:48 PM, Grygorii Strashko
>> <grygorii.strashko@ti.com> wrote:
>>> The below backtrace can be observed on -rt kernel with 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
>>> to simplify code analize in the future.
>>
>> Hm, yes, good point. It's only every called while other CPUs are stopped.
>>
>>>
>>> Cc: Kees Cook <keescook@chromium.org>
>>> Cc: Laura Abbott <labbott@redhat.com>
>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
>>> ---
>>>  arch/arm/mm/init.c | 8 +++-----
>>>  1 file changed, 3 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
>>> index 370581a..a77953a 100644
>>> --- a/arch/arm/mm/init.c
>>> +++ b/arch/arm/mm/init.c
>
> /**
>  * update_sections_early intended to be called only through stop_machine
>  * framework and be executed by only one CPU while all other CPUs will spin and
>  * wait, so no locking is required in this function.
>  */
>>> @@ -693,30 +693,28 @@ static void update_sections_early(struct section_perm perms[], int n)
>>
>> Maybe this should be renamed update_sections_stopped()? Or at least
>> comments added to help see why it's safe.
>
> would it be ok if I add above comment before update_sections_early?

A comment is fine. It'll just help people looking at this in the future. :)

Thanks!

-Kees

-- 
Kees Cook
Pixel Security

^ permalink raw reply	[flat|nested] 4+ messages in thread

end of thread, other threads:[~2017-04-19 20:01 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-04-18 20:48 [v4.9-rt PATCH] ARM: mm: remove tasklist locking from update_sections_early() Grygorii Strashko
2017-04-19  0:15 ` Kees Cook
2017-04-19 19:58   ` Grygorii Strashko
2017-04-19 20:01     ` Kees Cook

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).