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Message-ID: <20120201171856.GC2382@linux.vnet.ibm.com>
Date: Wed, 1 Feb 2012 09:18:56 -0800
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>,
linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: rcu warnings cause stack overflow
On Wed, Feb 01, 2012 at 04:14:48PM +0100, Frederic Weisbecker wrote:
> On Wed, Feb 01, 2012 at 11:06:52AM +0100, Heiko Carstens wrote:
> > Hi Frederic,
> >
> > your patch 00f49e5729 "rcu: Warn when rcu_read_lock() is used in extended
> > quiescent state" adds a WARN_ON_ONCE to rcu_lock_acquire().
> > Actually this found a bug on s390 (thanks!) but it probably didn't work
> > as expected.
> > On architectures which implement WARN_ON_ONCE with an exception this
> > additional warning will lead to a stack overflow (if it triggers):
> >
> > [ 55.746956] Kernel stack overflow.
> > [ 55.746966] Modules linked in: qeth_l3 binfmt_misc dm_multipath scsi_dh dm_mod qeth vmur ccwgroup [last unloaded: scsi_wait_
> > scan]
> > [ 55.746999] CPU: 0 Not tainted 3.3.0-rc1-00167-gf8275f9 #90
> > [ 55.747005] Process swapper/0 (pid: 0, task: 0000000000911100, ksp: 0000000000907d50)
> > [ 55.747013] Krnl PSW : 0404000180000000 00000000005d5728 (illegal_op+0x1c/0x134)
> > [ 55.747034] R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:0 CC:0 PM:0 EA:3
> > [ 55.747043] Krnl GPRS: 0000000000000001 00000000005d570c 00000000009040e8 0000000000000002
> > [ 55.747054] 00000000005d83dc ffffffffffffffff 0000000000000000 0400000000907cc8
> > [ 55.747064] 0404100180000000 00000000005d8478 0000000000000008 00000000009040e8
> > [ 55.747074] 0000000000904000 00000000005dc550 0000000000904048 0000000000904048
> > [ 55.747096] Krnl Code: 00000000005d571c: b90400ef lgr %r14,%r15
> > [ 55.747118] 00000000005d5720: b90400b2 lgr %r11,%r2
> > [ 55.747194] #00000000005d5724: a7840001 brc 8,5d5726
> > [ 55.747205] >00000000005d5728: a7fbff18 aghi %r15,-232
> > [ 55.747216] 00000000005d572c: e3e0f0980024 stg %r14,152(%r15)
> > [ 55.747228] 00000000005d5732: e31020100004 lg %r1,16(%r2)
> > [ 55.747242] 00000000005d5738: 58c020a0 l %r12,160(%r2)
> > [ 55.747257] 00000000005d573c: 91012009 tm 9(%r2),1
> > [ 55.747276] Call Trace:
> > [ 55.747282] ([<00000000005d60b4>] pgm_check_handler+0x154/0x158)
> > [ 55.747296] [<00000000005d8478>] __atomic_notifier_call_chain+0xd8/0xfc
> > [ 55.747309] ([<00000000005d83dc>] __atomic_notifier_call_chain+0x3c/0xfc)
> > [ 55.747322] [<00000000005d84c6>] atomic_notifier_call_chain+0x2a/0x3c
> > [ 55.747335] [<00000000005d852a>] notify_die+0x52/0x60
> > [ 55.747349] [<00000000005d57da>] illegal_op+0xce/0x134
> > [ 55.747364] [<00000000005d60b4>] pgm_check_handler+0x154/0x158
> >
> > [...lots more of the same...]
> >
> > [ 55.747379] [<00000000005d8478>] __atomic_notifier_call_chain+0xd8/0xfc
> > [ 55.747425] ([<00000000005d83dc>] __atomic_notifier_call_chain+0x3c/0xfc)
> > [ 55.747432] [<00000000005d84c6>] atomic_notifier_call_chain+0x2a/0x3c
> > [ 55.747440] [<00000000005d852a>] notify_die+0x52/0x60
> > [ 55.747448] [<00000000005d57da>] illegal_op+0xce/0x134
> > [ 55.747457] [<00000000005d60b4>] pgm_check_handler+0x154/0x158
> > [ 55.747797] [<00000000005d8478>] __atomic_notifier_call_chain+0xd8/0xfc
> > [ 55.747806] ([<00000000005d83dc>] __atomic_notifier_call_chain+0x3c/0xfc)
> > [ 55.747816] [<00000000005d84c6>] atomic_notifier_call_chain+0x2a/0x3c
> > [ 55.747826] [<00000000005d852a>] notify_die+0x52/0x60
> > [ 55.748456] [<00000000005d57da>] illegal_op+0xce/0x134
> > [ 55.748463] [<00000000005d60b4>] pgm_check_handler+0x154/0x158
> > [ 55.748472] [<000000000017afa0>] select_task_rq_fair+0x1478/0x14b4
> > [ 55.748483] ([<0000000000179bb8>] select_task_rq_fair+0x90/0x14b4)
> > [ 55.748493] [<0000000000170702>] try_to_wake_up+0x136/0x47c
> > [ 55.748506] [<000000000015b446>] autoremove_wake_function+0x26/0x58
> > [ 55.748518] [<000000000016693a>] __wake_up_common+0x76/0xb4
> > [ 55.748530] [<000000000016aed0>] __wake_up+0x4c/0x60
> > [ 55.748541] [<0000000000109ee0>] s390_handle_mcck+0x194/0x1f8
> > [ 55.748557] [<000000000010486a>] cpu_idle+0x192/0x1c0
> > [ 55.748570] [<0000000000977916>] start_kernel+0x402/0x410
> > [ 55.748588] [<0000000000100020>] _stext+0x20/0x80
> > [ 55.748603] 2 locks held by swapper/0/0:
> > [ 55.748612] #0: (crw_handler_wait_q.lock){......}, at: [<000000000016aeb6>] __wake_up+0x32/0x60
> > [ 55.748648] #1: (&p->pi_lock){-.-.-.}, at: [<000000000017060c>] try_to_wake_up+0x40/0x47c
> > [ 55.748663] Last Breaking-Event-Address:
> > [ 55.748667] [<0000000000000000>] 0x0
> >
> > This simply happens because WARN_ON_ONCE causes an exception, the excpetion
> > handler wants to call a notifier call chain (notify_die), which again uses
> > rcu_read_lock(), which again causes an exception and so on...
> > Unfortunately WARN_ON_ONCE first causes an exception and only afterwards sets
> > the flag that the warning already happened. Seems to be quite some effort to
> > change this behaviour.
> >
> > Removing the WARN_ON_ONCE will fix this and, if lockdep is turned on, still
> > will find illegal uses. But it won't work for lockdep off configs...
> > So we probably want something better than the patch below.
>
> Ah ok. Hmm, but why are you using an exception to implement WARN_ON()
> in s390? Is it to have a whole new stack for the warning path in order
> to avoid stack overflow from the place that called the WARN_ON() ?
>
> Anyway perhaps we need a recursion protection on WARN_ON_ONCE(), such
> as:
This makes sense to me, but I am also taking Heiko's patch
removing the WARN_ON()s in favor of the lockdep checks now in
rcu_read_lock_held(). After all, the rcu_lock_acquire() WARN_ON_ONCE()
only appears if PROVE_LOCKING=y, so the added requirement is not a
big deal. Also, CONFIG_PROVE_RCU is in the testing requirements in
Documentation/SubmitChecklist.
Thanx, Paul
> diff --git a/include/asm-generic/bug.h b/include/asm-generic/bug.h
> index 84458b0..f76635f 100644
> --- a/include/asm-generic/bug.h
> +++ b/include/asm-generic/bug.h
> @@ -137,9 +137,13 @@ extern void warn_slowpath_null(const char *file, const int line);
> static bool __warned; \
> int __ret_warn_once = !!(condition); \
> \
> - if (unlikely(__ret_warn_once)) \
> - if (WARN_ON(!__warned)) \
> + if (unlikely(__ret_warn_once)) { \
> + if (!__warned) { \
> __warned = true; \
> + barrier(); \
> + WARN_ON(1); \
> + } \
> + } \
> unlikely(__ret_warn_once); \
> })
>
>
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