Re: [v4.9-rt PATCH v2] ARM: mm: remove tasklist locking from update_sections_early()

[Grygorii Strashko]

On 04/21/2017 06:11 PM, Kees Cook wrote:
> On Wed, Apr 19, 2017 at 5:36 PM, Laura Abbott <labbott@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
>
> 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