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Message-ID: <1570550917.5576.303.camel@lca.pw>
Date: Tue, 08 Oct 2019 12:08:37 -0400
From: Qian Cai <cai@....pw>
To: Christian Borntraeger <borntraeger@...ibm.com>,
Michal Hocko <mhocko@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Peter Oberparleiter <oberpar@...ux.ibm.com>
Cc: akpm@...ux-foundation.org, sergey.senozhatsky.work@...il.com,
rostedt@...dmis.org, peterz@...radead.org, linux-mm@...ck.org,
john.ogness@...utronix.de, david@...hat.com,
linux-kernel@...r.kernel.org,
Heiko Carstens <heiko.carstens@...ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()
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@lca.pw
> > > > Petr has explained it is a false positive
> > > > http://lkml.kernel.org/r/20191007143002.l37bt2lzqtnqjqxu@pathway.suse.cz]
> > > > 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: [ 3.654307] WARNING: possible circular locking dependency detected
00: [ 3.654309] 5.4.0-rc1-next-20191004+ #4 Not tainted
00: [ 3.654311] ------------------------------------------------------
00: [ 3.654313] swapper/0/1 is trying to acquire lock:
00: [ 3.654314] 00000000553f3fb8 (sclp_lock){-.-.}, at: sclp_add_request+0x34
00: /0x308
00: [ 3.654320]
00: [ 3.654322] but task is already holding lock:
00: [ 3.654323] 00000000550c9fc0 (console_owner){....}, at: console_unlock+0x
00: 328/0xa30
00: [ 3.654329]
00: [ 3.654331] which lock already depends on the new lock.
00: [ 3.654332]
00: [ 3.654333]
00: [ 3.654335] the existing dependency chain (in reverse order) is:
00: [ 3.654336]
00: [ 3.654337] -> #3 (console_owner){....}:
00: [ 3.654343] lock_acquire+0x21a/0x468
00: [ 3.654345] console_unlock+0x3a6/0xa30
00: [ 3.654346] vprintk_emit+0x184/0x3c8
00: [ 3.654348] vprintk_default+0x44/0x50
00: [ 3.654349] printk+0xa8/0xc0
00: [ 3.654351] get_random_u64+0x40/0x108
00: [ 3.654360] add_to_free_area_random+0x188/0x1c0
00: [ 3.654364] free_one_page+0x72/0x128
00: [ 3.654366] __free_pages_ok+0x51c/0xca0
00: [ 3.654368] memblock_free_all+0x30a/0x3b0
00: [ 3.654370] mem_init+0x84/0x200
00: [ 3.654371] start_kernel+0x384/0x6a0
00: [ 3.654373] startup_continue+0x70/0xd0
00: [ 3.654374]
00: [ 3.654375] -> #2 (&(&zone->lock)->rlock){....}:
00: [ 3.654382] lock_acquire+0x21a/0x468
00: [ 3.654383] _raw_spin_lock+0x54/0x68
00: [ 3.654385] get_page_from_freelist+0x8b6/0x2d28
00: [ 3.654387] __alloc_pages_nodemask+0x246/0x658
00: [ 3.654389] alloc_slab_page+0x43c/0x858
00: [ 3.654390] allocate_slab+0x90/0x6f0
00: [ 3.654392] new_slab+0x88/0x90
00: [ 3.654393] ___slab_alloc+0x600/0x988
00: [ 3.654395] __slab_alloc+0x5a/0x90
00: [ 3.654396] kmem_cache_alloc+0x340/0x4c0
00: [ 3.654398] fill_pool+0x27a/0x498
00: [ 3.654400] __debug_object_init+0xa8/0x858
00: [ 3.654401] debug_object_activate+0x208/0x370
00: [ 3.654403] __call_rcu+0xb6/0x4a8
00: [ 3.654405] unregister_external_irq+0x13a/0x140
00: [ 3.654406] sclp_init+0x5e0/0x688
00: [ 3.654408] sclp_register+0x2e/0x248
00: [ 3.654409] sclp_rw_init+0x4a/0x70
00: [ 3.654411] sclp_console_init+0x4a/0x1b8
00: [ 3.654413] console_init+0x2c8/0x410
00: [ 3.654414] start_kernel+0x530/0x6a0
00: [ 3.654416] startup_continue+0x70/0xd0
00: [ 3.654417]
00: [ 3.654418] -> #1 (ext_int_hash_lock){....}:
00: [ 3.654424] lock_acquire+0x21a/0x468
00: [ 3.654426] _raw_spin_lock_irqsave+0xcc/0xe8
00: [ 3.654427] register_external_irq+0xb6/0x138
00: [ 3.654429] sclp_init+0x212/0x688
00: [ 3.654430] sclp_register+0x2e/0x248
00: [ 3.654432] sclp_rw_init+0x4a/0x70
00: [ 3.654434] sclp_console_init+0x4a/0x1b8
00: [ 3.654435] console_init+0x2c8/0x410
00: [ 3.654437] start_kernel+0x530/0x6a0
00: [ 3.654438] startup_continue+0x70/0xd0
00: [ 3.654439]
00: [ 3.654440] -> #0 (sclp_lock){-.-.}:
00: [ 3.654446] check_noncircular+0x338/0x3e0
00: [ 3.654448] __lock_acquire+0x1e66/0x2d88
00: [ 3.654450] lock_acquire+0x21a/0x468
00: [ 3.654451] _raw_spin_lock_irqsave+0xcc/0xe8
00: [ 3.654453] sclp_add_request+0x34/0x308
00: [ 3.654455] sclp_conbuf_emit+0x100/0x138
00: [ 3.654456] sclp_console_write+0x96/0x3b8
00: [ 3.654458] console_unlock+0x6dc/0xa30
00: [ 3.654460] vprintk_emit+0x184/0x3c8
00: [ 3.654461] vprintk_default+0x44/0x50
00: [ 3.654463] printk+0xa8/0xc0
00: [ 3.654464] iommu_debugfs_setup+0xf2/0x108
00: [ 3.654466] iommu_init+0x6c/0x78
00: [ 3.654467] do_one_initcall+0x162/0x680
00: [ 3.654469] kernel_init_freeable+0x4e8/0x5a8
00: [ 3.654471] kernel_init+0x2a/0x188
00: [ 3.654472] ret_from_fork+0x30/0x34
00: [ 3.654474] kernel_thread_starter+0x0/0xc
00: [ 3.654475]
00: [ 3.654476] other info that might help us debug this:
00: [ 3.654477]
00: [ 3.654479] Chain exists of:
00: [ 3.654480] sclp_lock --> &(&zone->lock)->rlock --> console_owner
00: [ 3.654488]
00: [ 3.654489] Possible unsafe locking scenario:
00: [ 3.654490]
00: [ 3.654492] CPU0 CPU1
00: [ 3.654493] ---- ----
00: [ 3.654495] lock(console_owner);
00: [ 3.654498] lock(&(&zone->lock)->rlock);
00: [ 3.654503] lock(console_owner);
00: [ 3.654506] lock(sclp_lock);
00: [ 3.654509]
00: [ 3.654511] *** DEADLOCK ***
00: [ 3.654512]
00: [ 3.654513] 2 locks held by swapper/0/1:
00: [ 3.654514] #0: 00000000550ca200 (console_lock){+.+.}, at: vprintk_emit+
00: 0x178/0x3c8
00: [ 3.654521] #1: 00000000550c9fc0 (console_owner){....}, at: console_unlo
00: ck+0x328/0xa30
00: [ 3.654529]
00: [ 3.654530] stack backtrace:
00: [ 3.654532] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc1-next-2019
00: 1004+ #4
00: [ 3.654534] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0)
00: [ 3.654535] Call Trace:
00: [ 3.654537] ([<000000005431e218>] show_stack+0x110/0x1b0)
00: [ 3.654539] [<0000000054bdd926>] dump_stack+0x126/0x178
00: [ 3.654541] [<0000000054414b08>] check_noncircular+0x338/0x3e0
00: [ 3.654543] [<000000005441aaf6>] __lock_acquire+0x1e66/0x2d88
00: [ 3.654545] [<0000000054417e12>] lock_acquire+0x21a/0x468
00: [ 3.654547] [<0000000054c18cc4>] _raw_spin_lock_irqsave+0xcc/0xe8
00: [ 3.654549] [<00000000549f2e14>] sclp_add_request+0x34/0x308
00: [ 3.654551] [<00000000549fa7f0>] sclp_conbuf_emit+0x100/0x138
00: [ 3.654553] [<00000000549fa90e>] sclp_console_write+0x96/0x3b8
00: [ 3.654554] [<000000005442b634>] console_unlock+0x6dc/0xa30
00: [ 3.654556] [<000000005442de2c>] vprintk_emit+0x184/0x3c8
00: [ 3.654558] [<000000005442e0b4>] vprintk_default+0x44/0x50
00: [ 3.654560] [<000000005442eb60>] printk+0xa8/0xc0
00: [ 3.654562] [<000000005494ca3a>] iommu_debugfs_setup+0xf2/0x108
00: [ 3.654564] [<000000005557c0ec>] iommu_init+0x6c/0x78
00: [ 3.654566] [<0000000054300fda>] do_one_initcall+0x162/0x680
00: [ 3.654568] [<000000005553b9f0>] kernel_init_freeable+0x4e8/0x5a8
00: [ 3.654569] [<0000000054c04172>] kernel_init+0x2a/0x188
00: [ 3.654571] [<0000000054c19fbc>] ret_from_fork+0x30/0x34
00: [ 3.654573] [<0000000054c19fc0>] kernel_thread_starter+0x0/0xc
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