Re: [v3 PATCH] arm64: replace read_lock to rcu lock in call_break_hook

[Will Deacon]

On Thu, Oct 08, 2015 at 04:55:38PM -0700, Paul E. McKenney wrote:
> On Mon, Oct 05, 2015 at 02:32:51PM -0700, Yang Shi wrote:
> > BUG: sleeping function called from invalid context at kernel/locking/rtmutex.c:917
> > in_atomic(): 0, irqs_disabled(): 128, pid: 342, name: perf
> > 1 lock held by perf/342:
> >  #0:  (break_hook_lock){+.+...}, at: [<ffffffc0000851ac>] call_break_hook+0x34/0xd0
> > irq event stamp: 62224
> > hardirqs last  enabled at (62223): [<ffffffc00010b7bc>] __call_rcu.constprop.59+0x104/0x270
> > hardirqs last disabled at (62224): [<ffffffc0000fbe20>] vprintk_emit+0x68/0x640
> > softirqs last  enabled at (0): [<ffffffc000097928>] copy_process.part.8+0x428/0x17f8
> > softirqs last disabled at (0): [<          (null)>]           (null)
> > CPU: 0 PID: 342 Comm: perf Not tainted 4.1.6-rt5 #4
> > Hardware name: linux,dummy-virt (DT)
> > Call trace:
> > [<ffffffc000089968>] dump_backtrace+0x0/0x128
> > [<ffffffc000089ab0>] show_stack+0x20/0x30
> > [<ffffffc0007030d0>] dump_stack+0x7c/0xa0
> > [<ffffffc0000c878c>] ___might_sleep+0x174/0x260
> > [<ffffffc000708ac8>] __rt_spin_lock+0x28/0x40
> > [<ffffffc000708db0>] rt_read_lock+0x60/0x80
> > [<ffffffc0000851a8>] call_break_hook+0x30/0xd0
> > [<ffffffc000085a70>] brk_handler+0x30/0x98
> > [<ffffffc000082248>] do_debug_exception+0x50/0xb8
> > Exception stack(0xffffffc00514fe30 to 0xffffffc00514ff50)
> > fe20:                                     00000000 00000000 c1594680 0000007f
> > fe40: ffffffff ffffffff 92063940 0000007f 0550dcd8 ffffffc0 00000000 00000000
> > fe60: 0514fe70 ffffffc0 000be1f8 ffffffc0 0514feb0 ffffffc0 0008948c ffffffc0
> > fe80: 00000004 00000000 0514fed0 ffffffc0 ffffffff ffffffff 9282a948 0000007f
> > fea0: 00000000 00000000 9282b708 0000007f c1592820 0000007f 00083914 ffffffc0
> > fec0: 00000000 00000000 00000010 00000000 00000064 00000000 00000001 00000000
> > fee0: 005101e0 00000000 c1594680 0000007f c1594740 0000007f ffffffd8 ffffff80
> > ff00: 00000000 00000000 00000000 00000000 c1594770 0000007f c1594770 0000007f
> > ff20: 00665e10 00000000 7f7f7f7f 7f7f7f7f 01010101 01010101 00000000 00000000
> > ff40: 928e4cc0 0000007f 91ff11e8 0000007f
> > 
> > call_break_hook is called in atomic context (hard irq disabled), so replace
> > the sleepable lock to rcu lock, replace relevant list operations to rcu
> > version and call synchronize_rcu() in unregister_break_hook().
> > 
> > And, replace write lock to spinlock in {un}register_break_hook.
> > 
> > Signed-off-by: Yang Shi <yang.shi@xxxxxxxxxx>
> 
> Looks more plausible to me.  Does it look OK to you, Steven?

This is already in mainline as a fix, so please shout loudly if you think
it's broken (it looked ok to me and didn't cause any regressions in my
testing).

Will
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