Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

From: Qian Cai
Date: Tue Oct 08 2019 - 12:08:43 EST

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In reply to: Christian Borntraeger: "Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()"
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On Tue, 2019-10-08 at 14:56 +0200, Christian Borntraeger wrote:
> Adding Peter Oberparleiter.
> Peter, can you have a look?
>
> On 08.10.19 10:27, Michal Hocko wrote:
> > On Tue 08-10-19 09:43:57, Petr Mladek wrote:
> > > On Mon 2019-10-07 16:49:37, Michal Hocko wrote:
> > > > [Cc s390 maintainers - the lockdep is http://lkml.kernel.org/r/1570228005-24979-1-git-send-email-cai@xxxxxx
> > > > Petr has explained it is a false positive
> > > > http://lkml.kernel.org/r/20191007143002.l37bt2lzqtnqjqxu@xxxxxxxxxxxxxxx]
> > > > On Mon 07-10-19 16:30:02, Petr Mladek wrote:
> > > > [...]
> > > > > I believe that it cannot really happen because:
> > > > >
> > > > > static int __init
> > > > > sclp_console_init(void)
> > > > > {
> > > > > [...]
> > > > > rc = sclp_rw_init();
> > > > > [...]
> > > > > register_console(&sclp_console);
> > > > > return 0;
> > > > > }
> > > > >
> > > > > sclp_rw_init() is called before register_console(). And
> > > > > console_unlock() will never call sclp_console_write() before
> > > > > the console is registered.
> > > > >
> > > > > AFAIK, lockdep only compares existing chain of locks. It does
> > > > > not know about console registration that would make some
> > > > > code paths mutually exclusive.
> > > > >
> > > > > I believe that it is a false positive. I do not know how to
> > > > > avoid this lockdep report. I hope that it will disappear
> > > > > by deferring all printk() calls rather soon.
> > > >
> > > > Thanks a lot for looking into this Petr. I have also checked the code
> > > > and I really fail to see why the allocation has to be done under the
> > > > lock in the first place. sclp_read_sccb and sclp_init_sccb are global
> > > > variables but I strongly suspect that they need a synchronization during
> > > > early init, callbacks are registered only later IIUC:
> > >
> > > Good idea. It would work when the init function is called only once.
> > > But see below.
> > >
> > > > diff --git a/drivers/s390/char/sclp.c b/drivers/s390/char/sclp.c
> > > > index d2ab3f07c008..4b1c033e3255 100644
> > > > --- a/drivers/s390/char/sclp.c
> > > > +++ b/drivers/s390/char/sclp.c
> > > > @@ -1169,13 +1169,13 @@ sclp_init(void)
> > > > unsigned long flags;
> > > > int rc = 0;
> > > >
> > > > + sclp_read_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA);
> > > > + sclp_init_sccb = (void *) __get_free_page(GFP_ATOMIC | GFP_DMA);
> > > > spin_lock_irqsave(&sclp_lock, flags);
> > > > /* Check for previous or running initialization */
> > > > if (sclp_init_state != sclp_init_state_uninitialized)
> > > > goto fail_unlock;
> > >
> > > It seems that sclp_init() could be called several times in parallel.
> > > I see it called from sclp_register() and sclp_initcall().
> >
> > Interesting. Something for s390 people to answer I guess.
> > Anyway, this should be quite trivial to workaround by a cmpxch or alike.
> >

The above fix is simply insufficient,

00: [ÂÂÂÂ3.654307] WARNING: possible circular locking dependency detectedÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654309] 5.4.0-rc1-next-20191004+ #4 Not taintedÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654311] ------------------------------------------------------ÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654313] swapper/0/1 is trying to acquire lock:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654314] 00000000553f3fb8 (sclp_lock){-.-.}, at: sclp_add_request+0x34
00: /0x308ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654320]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654322] but task is already holding lock:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654323] 00000000550c9fc0 (console_owner){....}, at: console_unlock+0x
00: 328/0xa30ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654329]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654331] which lock already depends on the new lock.ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654332]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654333]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654335] the existing dependency chain (in reverse order) is:ÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654336]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654337] -> #3 (console_owner){....}:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654343]ÂÂÂÂÂÂÂÂlock_acquire+0x21a/0x468ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654345]ÂÂÂÂÂÂÂÂconsole_unlock+0x3a6/0xa30ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654346]ÂÂÂÂÂÂÂÂvprintk_emit+0x184/0x3c8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654348]ÂÂÂÂÂÂÂÂvprintk_default+0x44/0x50ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654349]ÂÂÂÂÂÂÂÂprintk+0xa8/0xc0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654351]ÂÂÂÂÂÂÂÂget_random_u64+0x40/0x108ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654360]ÂÂÂÂÂÂÂÂadd_to_free_area_random+0x188/0x1c0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654364]ÂÂÂÂÂÂÂÂfree_one_page+0x72/0x128ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654366]ÂÂÂÂÂÂÂÂ__free_pages_ok+0x51c/0xca0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654368]ÂÂÂÂÂÂÂÂmemblock_free_all+0x30a/0x3b0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654370]ÂÂÂÂÂÂÂÂmem_init+0x84/0x200ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654371]ÂÂÂÂÂÂÂÂstart_kernel+0x384/0x6a0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654373]ÂÂÂÂÂÂÂÂstartup_continue+0x70/0xd0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654374]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654375] -> #2 (&(&zone->lock)->rlock){....}:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654382]ÂÂÂÂÂÂÂÂlock_acquire+0x21a/0x468ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654383]ÂÂÂÂÂÂÂÂ_raw_spin_lock+0x54/0x68ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654385]ÂÂÂÂÂÂÂÂget_page_from_freelist+0x8b6/0x2d28ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654387]ÂÂÂÂÂÂÂÂ__alloc_pages_nodemask+0x246/0x658ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654389]ÂÂÂÂÂÂÂÂalloc_slab_page+0x43c/0x858ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654390]ÂÂÂÂÂÂÂÂallocate_slab+0x90/0x6f0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654392]ÂÂÂÂÂÂÂÂnew_slab+0x88/0x90ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654393]ÂÂÂÂÂÂÂÂ___slab_alloc+0x600/0x988ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654395]ÂÂÂÂÂÂÂÂ__slab_alloc+0x5a/0x90ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654396]ÂÂÂÂÂÂÂÂkmem_cache_alloc+0x340/0x4c0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654398]ÂÂÂÂÂÂÂÂfill_pool+0x27a/0x498ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654400]ÂÂÂÂÂÂÂÂ__debug_object_init+0xa8/0x858ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654401]ÂÂÂÂÂÂÂÂdebug_object_activate+0x208/0x370ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654403]ÂÂÂÂÂÂÂÂ__call_rcu+0xb6/0x4a8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654405]ÂÂÂÂÂÂÂÂunregister_external_irq+0x13a/0x140ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654406]ÂÂÂÂÂÂÂÂsclp_init+0x5e0/0x688ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654408]ÂÂÂÂÂÂÂÂsclp_register+0x2e/0x248ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654409]ÂÂÂÂÂÂÂÂsclp_rw_init+0x4a/0x70ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654411]ÂÂÂÂÂÂÂÂsclp_console_init+0x4a/0x1b8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654413]ÂÂÂÂÂÂÂÂconsole_init+0x2c8/0x410ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654414]ÂÂÂÂÂÂÂÂstart_kernel+0x530/0x6a0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654416]ÂÂÂÂÂÂÂÂstartup_continue+0x70/0xd0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654417]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654418] -> #1 (ext_int_hash_lock){....}:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654424]ÂÂÂÂÂÂÂÂlock_acquire+0x21a/0x468ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654426]ÂÂÂÂÂÂÂÂ_raw_spin_lock_irqsave+0xcc/0xe8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654427]ÂÂÂÂÂÂÂÂregister_external_irq+0xb6/0x138ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654429]ÂÂÂÂÂÂÂÂsclp_init+0x212/0x688ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654430]ÂÂÂÂÂÂÂÂsclp_register+0x2e/0x248ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654432]ÂÂÂÂÂÂÂÂsclp_rw_init+0x4a/0x70ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654434]ÂÂÂÂÂÂÂÂsclp_console_init+0x4a/0x1b8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654435]ÂÂÂÂÂÂÂÂconsole_init+0x2c8/0x410ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654437]ÂÂÂÂÂÂÂÂstart_kernel+0x530/0x6a0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654438]ÂÂÂÂÂÂÂÂstartup_continue+0x70/0xd0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654439]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654440] -> #0 (sclp_lock){-.-.}:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654446]ÂÂÂÂÂÂÂÂcheck_noncircular+0x338/0x3e0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654448]ÂÂÂÂÂÂÂÂ__lock_acquire+0x1e66/0x2d88ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654450]ÂÂÂÂÂÂÂÂlock_acquire+0x21a/0x468ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654451]ÂÂÂÂÂÂÂÂ_raw_spin_lock_irqsave+0xcc/0xe8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654453]ÂÂÂÂÂÂÂÂsclp_add_request+0x34/0x308ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654455]ÂÂÂÂÂÂÂÂsclp_conbuf_emit+0x100/0x138ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654456]ÂÂÂÂÂÂÂÂsclp_console_write+0x96/0x3b8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654458]ÂÂÂÂÂÂÂÂconsole_unlock+0x6dc/0xa30ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654460]ÂÂÂÂÂÂÂÂvprintk_emit+0x184/0x3c8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654461]ÂÂÂÂÂÂÂÂvprintk_default+0x44/0x50ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654463]ÂÂÂÂÂÂÂÂprintk+0xa8/0xc0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654464]ÂÂÂÂÂÂÂÂiommu_debugfs_setup+0xf2/0x108ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654466]ÂÂÂÂÂÂÂÂiommu_init+0x6c/0x78ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654467]ÂÂÂÂÂÂÂÂdo_one_initcall+0x162/0x680ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654469]ÂÂÂÂÂÂÂÂkernel_init_freeable+0x4e8/0x5a8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654471]ÂÂÂÂÂÂÂÂkernel_init+0x2a/0x188ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654472]ÂÂÂÂÂÂÂÂret_from_fork+0x30/0x34ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654474]ÂÂÂÂÂÂÂÂkernel_thread_starter+0x0/0xcÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654475]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654476] other info that might help us debug this:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654477]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654479] Chain exists of:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654480]ÂÂÂsclp_lock --> &(&zone->lock)->rlock --> console_ownerÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654488]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654489]ÂÂPossible unsafe locking scenario:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654490]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654492]ÂÂÂÂÂÂÂÂCPU0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂCPU1ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654493]ÂÂÂÂÂÂÂÂ----ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ----ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654495]ÂÂÂlock(console_owner);ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654498]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂlock(&(&zone->lock)->rlock);ÂÂ
00: [ÂÂÂÂ3.654503]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂlock(console_owner);ÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654506]ÂÂÂlock(sclp_lock);ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654509]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654511]ÂÂ*** DEADLOCK ***ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654512]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654513] 2 locks held by swapper/0/1:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654514]ÂÂ#0: 00000000550ca200 (console_lock){+.+.}, at: vprintk_emit+
00: 0x178/0x3c8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654521]ÂÂ#1: 00000000550c9fc0 (console_owner){....}, at: console_unlo
00: ck+0x328/0xa30ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654529]ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654530] stack backtrace:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654532] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc1-next-2019
00: 1004+ #4ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654534] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654535] Call Trace:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654537] ([<000000005431e218>] show_stack+0x110/0x1b0)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654539]ÂÂ[<0000000054bdd926>] dump_stack+0x126/0x178ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654541]ÂÂ[<0000000054414b08>] check_noncircular+0x338/0x3e0ÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654543]ÂÂ[<000000005441aaf6>] __lock_acquire+0x1e66/0x2d88ÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654545]ÂÂ[<0000000054417e12>] lock_acquire+0x21a/0x468ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654547]ÂÂ[<0000000054c18cc4>] _raw_spin_lock_irqsave+0xcc/0xe8ÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654549]ÂÂ[<00000000549f2e14>] sclp_add_request+0x34/0x308ÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654551]ÂÂ[<00000000549fa7f0>] sclp_conbuf_emit+0x100/0x138ÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654553]ÂÂ[<00000000549fa90e>] sclp_console_write+0x96/0x3b8ÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654554]ÂÂ[<000000005442b634>] console_unlock+0x6dc/0xa30ÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654556]ÂÂ[<000000005442de2c>] vprintk_emit+0x184/0x3c8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654558]ÂÂ[<000000005442e0b4>] vprintk_default+0x44/0x50ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654560]ÂÂ[<000000005442eb60>] printk+0xa8/0xc0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654562]ÂÂ[<000000005494ca3a>] iommu_debugfs_setup+0xf2/0x108ÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654564]ÂÂ[<000000005557c0ec>] iommu_init+0x6c/0x78ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654566]ÂÂ[<0000000054300fda>] do_one_initcall+0x162/0x680ÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654568]ÂÂ[<000000005553b9f0>] kernel_init_freeable+0x4e8/0x5a8ÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654569]ÂÂ[<0000000054c04172>] kernel_init+0x2a/0x188ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654571]ÂÂ[<0000000054c19fbc>] ret_from_fork+0x30/0x34ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂÂÂ3.654573]ÂÂ[<0000000054c19fc0>] kernel_thread_starter+0x0/0xcÂ

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