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Subject: Re: [v4.9-rt PATCH v2] ARM: mm: remove tasklist locking from
 update_sections_early()
To: Kees Cook <keescook@chromium.org>, Laura Abbott <labbott@redhat.com>
References: <20170419201047.31578-1-grygorii.strashko@ti.com>
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 <CAGXu5jKZR7=QmhW2uruJDxTsF_+CLd4Bp8D1NU4AvjorP8mbsg@mail.gmail.com>
CC: Russell King <linux@armlinux.org.uk>,
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From: Grygorii Strashko <grygorii.strashko@ti.com>
Message-ID: <cbd5bb0f-7c1f-c53c-d732-df08b9259f80@ti.com>
Date: Tue, 25 Apr 2017 15:22:37 -0500
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On 04/21/2017 06:11 PM, Kees Cook wrote:
> On Wed, Apr 19, 2017 at 5:36 PM, Laura Abbott <labbott@redhat.com> wrote:
>> On 04/19/2017 01:10 PM, Grygorii Strashko 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
>>
>> Acked-by: Laura Abbott <labbott@redhat.com>
>
> Acked-by: Kees Cook <keescook@chromium.org>
>
> Please throw this at the ARM patch tracker (with our Acks).
> http://www.arm.linux.org.uk/developer/patches/info.php
>

Done
  http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=8672/1

-- 
regards,
-grygorii